U.S. patent application number 16/449157 was filed with the patent office on 2019-10-17 for scalable, real-time messaging system.
The applicant listed for this patent is Satori Worldwide, LLC. Invention is credited to Fredrik Erik Linder, Lev Walkin.
Application Number | 20190319901 16/449157 |
Document ID | / |
Family ID | 59078217 |
Filed Date | 2019-10-17 |
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United States Patent
Application |
20190319901 |
Kind Code |
A1 |
Walkin; Lev ; et
al. |
October 17, 2019 |
SCALABLE, REAL-TIME MESSAGING SYSTEM
Abstract
Methods, systems, and apparatus, including computer programs
encoded on a computer storage medium, for balancing loads in a
publish-subscribe system. An example method includes identifying,
by one or more computer processors, a first node from a plurality
of nodes in a publish-subscribe system based at least in pan on (i)
node-specific data representing loads on the plurality of nodes and
(ii) channel-specific data representing a load associated with a
channel comprising a channel portion to be temporarily offloaded
from a second node. The method also includes selecting, by the one
or more computer processors, the first node to temporarily host the
channel portion of the channel. The method further includes
receiving a request to access the channel portion, and granting the
request to access the channel portion.
Inventors: |
Walkin; Lev; (Santa Clara,
CA) ; Linder; Fredrik Erik; (Dublin, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Satori Worldwide, LLC |
Palo Alto |
CA |
US |
|
|
Family ID: |
59078217 |
Appl. No.: |
16/449157 |
Filed: |
June 21, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15244380 |
Aug 23, 2016 |
10374986 |
|
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16449157 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 51/14 20130101;
H04L 51/04 20130101; H04L 67/1008 20130101 |
International
Class: |
H04L 12/58 20060101
H04L012/58; H04L 29/08 20060101 H04L029/08 |
Claims
1. A method, comprising: identifying, by one or more computer
processors, a first node from a plurality of nodes in a
publish-subscribe system based at least in part on (i)
node-specific data representing loads on the plurality of nodes and
(ii) channel-specific data representing a load associated with a
channel comprising a channel portion to be temporarily offloaded
from a second node; selecting, by the one or more computer
processors, the first node to temporarily host the channel portion
of the channel; receiving a request to access the channel portion;
and granting the request to access the channel portion.
2. The method of claim 1, wherein the node-specific data comprises
at least one of: a number of channel portions being temporarily
hosted by the respective nodes, a data reception rate of the
respective nodes, a data transmission rate of the respective nodes,
a storage utilization of the respective nodes, or a processing rate
of the respective nodes.
3. The method of claim 1, wherein the channel-specific data
comprises at least one of: a number of subscribers to the channel,
a number of publishers to the channel, a rate at which messages are
published to the channel, a rate at which messages are read from
the channel, a number of nodes having permission to access the
channel, or a channel portion size for the channel.
4. The method of claim 1, wherein selecting the first node to
temporarily host the channel portion of the channel comprises:
sending a request to the first node to temporarily host the channel
portion of the channel.
5. The method of claim 4, wherein the request to the first node to
temporarily host the channel portion comprises an indication for
one or more messages published to the channel to be temporarily
stored and for access to the one or more messages to be temporarily
provided to a plurality of subscribers, and wherein the one or more
messages were previously stored on the second node.
6. The method of claim 1, comprising: receiving at least a portion
of the node-specific data from the plurality of nodes.
7. The method of claim 1, comprising: determining at least a
portion of the node-specific data based on received requests to
access the channel portion and on granted requests to access the
channel portion.
8. The method of claim 1, wherein identifying the first node from
the plurality of nodes comprises: determining, based at least in
part on the node-specific data, that a load on the first node is
lowest among respective loads on the nodes; and identifying the
first node based on the determination.
9. The method of claim 1, wherein identifying the first node from
the plurality of nodes comprises: determining, based at least in
part on the node-specific data, that a load on the first node is
below a threshold load level; and identifying the first node based
on the determination.
10. The method of claim 1, wherein selecting the first node from
the plurality of nodes comprises: determining, based at least in
part on a portion of the node-specific data corresponding to the
first node and on a portion of the channel-specific data
corresponding to the channel, an expected load on the first node
that would result from the first node hosting the portion of the
channel; determining that the expected load on the first node is
below a threshold load level; and identifying the first node based
on the determination that the expected load on the first node is
below the threshold load level.
11. A system, comprising: one or more computer processors
programmed to perform operations to: identify a first node from a
plurality of nodes in a publish-subscribe system based at least in
part on (i) node-specific data representing loads on the plurality
of nodes and (ii) channel-specific data representing a load
associated with a channel comprising a channel portion to be
temporarily offloaded from a second node; select the first node to
temporarily host the channel portion of the channel; receive a
request to access the channel portion; and grant the request to
access the channel portion.
12. The system of claim 11, wherein the node-specific data
comprises at least one of: a number of channel portions being
temporarily hosted by the respective nodes, a data reception rate
of the respective nodes, a data transmission rate of the respective
nodes, a storage utilization of the respective nodes, or a
processing rate of the respective nodes.
13. The system of claim 11, wherein the channel-specific data
comprises at least one of: a number of subscribers to the channel,
a number of publishers to the channel, a rate at which messages are
published to the channel, a rate at which messages are read from
the channel, a number of nodes having permission to access the
channel, or a channel portion size for the channel.
14. The system of claim 11, wherein to select the first node to
temporarily host the channel portion of the channel the one or more
computer processors are further to: send a request to the first
node to temporarily host the channel portion of the channel.
15. The system of claim 14, wherein the request to the first node
to temporarily host the channel portion comprises an indication for
one or more messages published to the channel to be temporarily
stored and for access to the one or more messages to be temporarily
provided to a plurality of subscribers, and wherein the one or more
messages were previously stored on the second node.
16. The system of claim 11, wherein the operations are further to:
receive at least a portion of the node-specific data from the
plurality of nodes.
17. The system of claim 11, wherein the operations are further to:
determine at least a portion of the node-specific data based on
received requests to access the channel portion and on granted
requests to access the channel portion.
18. The system of claim 11, wherein to identify the first node from
the plurality of nodes the one or more computer processors are
further to: determine, based at least in part on the node-specific
data, that a load on the first node is lowest among respective
loads on the nodes; and identify the first node based on the
determination.
19. The system of claim 11, wherein to identify the first node from
the plurality of nodes the one or more computer processors are
further to: determine, based at least in part on the node-specific
data, that a load on the first node is below a threshold load
level; and identify the first node based on the determination.
20. A non-transitory computer-readable medium having instructions
stored thereon that, when executed by one or more computer
processors, cause the one or more computer processors to: identify,
by the one or more computer processors, a first node from a
plurality of nodes in a publish-subscribe system based at least in
part on (i) node-specific data representing loads on the plurality
of nodes and (ii) channel-specific data representing a load
associated with a channel comprising a channel portion to be
temporarily offloaded from a second node; select, by the one or
more computer processors, the first node to temporarily host the
channel portion of the channel; receive a request to access the
channel portion; and grant the request to access the channel
portion.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 15/244,380, filed Aug. 23, 2016, the entire contents of which
are incorporated by reference herein.
BACKGROUND
[0002] This specification relates to a data communication system
and, in particular, a system that implements real-time, scalable
publish-subscribe messaging.
[0003] The publish-subscribe pattern (or "PubSub") is a data
communication messaging arrangement implemented by software systems
where so-called publishers publish messages to topics and so-called
subscribers receive the messages pertaining to particular topics to
which they are subscribed. There can be one or more publishers per
topic and publishers generally have no knowledge of what
subscribers, if any, will receive the published messages. Some
PubSub systems do not cache messages or have small caches meaning
that subscribers may not receive messages that were published
before the time of subscription to a particular topic. PubSub
systems can be susceptible to performance instability during surges
of message publications or as the number of subscribers to a
particular topic increases.
SUMMARY
[0004] In general, one aspect of the subject matter described in
this specification can be embodied in a computer-implemented
load-balancing method for a publish-subscribe system. The method
includes identifying, by one or more computer processors, a first
node from a plurality of nodes in a publish-subscribe system based
at least in part on (i) node-specific data representing loads on
the plurality of nodes and (ii) channel-specific data representing
a load associated with a channel comprising a channel portion to be
temporarily offloaded from a second node; selecting, by the one or
more computer processors, the first node to temporarily host the
channel portion of the channel; receiving a request to access the
channel portion; and granting the request to access the channel
portion.
[0005] Elements of embodiments or examples described with respect
to a given aspect of the invention can be used in various
embodiments or examples of another aspect of the invention. For
example, it is contemplated that features of dependent claims
depending from one independent claim can be used in apparatus,
systems, and/or methods of any of the other independent claims.
[0006] The details of one or more embodiments of the subject matter
described in this specification are set forth in the accompanying
drawings and the description below. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A illustrates an example system that supports the
PubSub communication pattern.
[0008] FIG. 1B illustrates functional layers of software on an
example client device.
[0009] FIG. 2 is a diagram of an example messaging system.
[0010] FIG. 3A is a data flow diagram of an example method for
writing data to a streamlet.
[0011] FIG. 3B is a data flow diagram of an example method for
reading data from a streamlet.
[0012] FIG. 4A is a data flow diagram of an example method for
publishing messages to a channel of a messaging system.
[0013] FIG. 4B is a data flow diagram of an example method for
subscribing to a channel of a messaging system.
[0014] FIG. 4C is an example data structure for storing messages of
a channel of a messaging system.
[0015] FIG. 5 is a flowchart of an example method for storing
messages of a messaging system.
DETAILED DESCRIPTION
[0016] FIG. 1A illustrates an example system 100 that supports the
PubSub communication pattern. Publisher (e.g., Publishers 1-N) can
publish messages to named channels (e.g., Channels I-N) by way of
the system 100 (also referred to as "messaging system" hereafter).
A message can include any type of information including one or more
of the following: text, image content, sound content, multimedia
content, video content, binary data, and so on. Other types of
message data are possible. Subscribers (e.g., Subscribers 1-N2) can
subscribe to a named channel using the system 100 and start
receiving messages which occur after the subscription request or
from a given position (e.g., a message number or time offset). A
client can be both a publisher and a subscriber.
[0017] Depending on the configuration, a PubSub system can be
categorized as follows: [0018] One to One (1:1). In this
configuration there is one publisher and one subscriber per
channel. A typical use case is private messaging. [0019] One to
Many (1:N). In this configuration there is one publisher and
multiple subscribers per channel. Typical use cases are
broadcasting messages (e.g., stock prices). [0020] Many to Many
(M:N). In this configuration there are many publishers publishing
to a single channel. The messages are then delivered to multiple
subscribers. Typical use cases are map applications.
[0021] There is no separate operation needed to create a named
channel. A channel is created implicitly when the channel is
subscribed to or when a message is published to the channel. In
some implementations, channel names can be qualified by a name
space. A name space comprises one or more channel names. Different
name spaces can have the same channel names without causing
ambiguity. The name space name can be a prefix of a channel name
where the name space and channel name are separated by a dot or
other suitable separator. In some implementations, name spaces can
be used when specifying channel authorization settings. For
instance, the messaging system 100 may have app1.foo and
app1.system.notifications channels where "app1" is the name of the
name space. The system can allow clients to subscribe and publish
to the app1.foo channel. However, clients can only subscribe to,
but not publish to the app1.system.notifications channel.
[0022] FIG. 1B illustrates functional layers of software on an
example client device. A client device (e.g., client 102) is a data
processing apparatus such as, for example, a personal computer, a
laptop computer, a tablet computer, a smart phone, a smart watch,
or a server computer. Other types of client devices are possible.
The application layer 104 comprises the end-user application(s)
that will integrate with the system 100. The messaging layer 106 is
a programmatic interface for the application layer 104 to utilize
services of the system 100 such as channel subscription, message
publication, message retrieval, user authentication, and user
authorization. In some implementations, the messages passed to and
from the messaging layer 106 are encoded as JavaScript Object
Notation (JSON) objects. Other message encoding schemes are
possible.
[0023] The operating system layer 108 includes the operating system
software on the client 102. In various implementations, messages
can be sent and received to/from the system 100 using persistent or
non-persistent connections. Persistent connections can be created
using, for example, network sockets. A transport protocol such as
TCP/IP layer 112 implements the Transport Control Protocol/Internet
Protocol communication with the system 100 that can be used by the
messaging layer 106 to send messages over connections to the system
100. Other communication protocols are possible including, for
example, User Datagram Protocol (UDP). In further implementations,
an optional Transport Layer Security (TLS) layer 110 can be
employed to ensure the confidentiality of the messages.
[0024] FIG. 2 is a diagram of an example messaging system 100. The
messaging system 100 provides functionality for implementing PubSub
communication patterns. The system includes software components and
storage that can be deployed at one or more data centers 122 in one
or more geographic locations, for example. The system includes
multiplier (MX) nodes (e.g., MX nodes or multiplexer nodes 202, 204
and 206), queue (Q) nodes (e.g., Q nodes or queue nodes 208, 210
and 212), one or more channel manager nodes (e.g., channel managers
214, 215), and optionally one or more cache (C) nodes nodes 220 and
222. Each node can execute in a virtual machine or on a physical
machine (e.g., a data processing apparatus). Each MX node serves as
a termination point for one or more publisher and/or subscriber
connections through the external network 216. The internal
communication among MX nodes, Q nodes, C nodes, and the channel
manager, is conducted over an internal network 218, for example. By
way of illustration, MX node 204 can be the terminus of a
subscriber connection from client 102. Each Q node buffers channel
data for consumption by the MX nodes. An ordered sequence of
messages published to a channel is a logical channel stream. For
example, if three clients publish messages to a given channel, the
combined messages published by the clients comprise a channel
stream. Messages can be ordered in a channel stream, for example,
by time of publication by the client, by time of receipt by an MX
node, or by time of receipt by a Q node. Other ways for ordering
messages in a channel stream are possible. In the case where more
than one message would be assigned to the same position in the
order one of the messages can be chosen (e.g., randomly) to have a
later sequence in the order. Each channel manager node is
responsible for managing Q node load by splitting channel streams
into streamlets (also referred to herein as "channel portions").
Streamlets are discussed further below. The optional C nodes
provide caching and load removal from the Q nodes. Q nodes may also
be referred to herein as "hosting nodes." MX nodes may also be
referred to herein as "interface nodes."
[0025] In the example messaging system 100, one or more client
devices (publishers and/or subscribers) establish respective
persistent connections (e.g., TCP connections) to an MX node (e.g.,
MX nodes 202, 204 and/or 206). The MX node serves as a termination
point for these connections. For instance, external messages (e.g.,
between respective client devices and the MX node) carried by these
connections can be encoded based on an external protocol (e.g.,
JSON). The MX node terminates the external protocol and translates
the external messages to internal communication, and vice versa.
The MX nodes publish and subscribe to streamlets on behalf of
clients. In this way, an MX node can multiplex and merge requests
of client devices subscribing for or publishing to the same
channel, thus representing multiple client devices as one, instead
of one by one.
[0026] In the example messaging system 100, a Q node (e.g., Q node
208) can store one or more streamlets of one or more channel
streams. A streamlet is a data buffer for a portion of a channel
stream. A streamlet will close to writing when its storage is full.
A streamlet will close to reading and writing and be de-allocated
when its time-to-live (TTL) has expired. By way of illustration, a
streamlet can have a maximum size of 1 MB and a TTL of three
minutes. Different channels can have streamlets limited by
different sizes and/or by different TTLs. For instance, streamlets
in one channel can exist for up to three minutes, while streamlets
in another channel can exist for up to 10 minutes. In various
implementations, a streamlet corresponds to a computing process
running on a Q node. The computing process can be terminated after
the streamlet's TTL has expired, thus freeing up computing
resources (for the streamlet) back to the Q node, for example.
[0027] When receiving a publish request from client 102, an MX node
(e.g., MX node 204) makes a request to a channel manager (e.g.,
channel manager 214) to grant access to a streamlet to write the
message being published. Note, however, that if the MX node has
already been granted write access to a streamlet for the channel
(and the channel has not been closed to writing), the MX node can
write the message to that streamlet without having to request a
grant to access the streamlet. Once a message is written to a
streamlet for a channel, the message can be read by MX nodes and
provided to subscribers of that channel.
[0028] Similarly, when receiving a channel subscription request
from a client device, an MX node makes a request to a channel
manager to grant access to a streamlet for the channel from which
messages are read. If the MX node has already been granted read
access to a streamlet for the channel (and the channel's TTL has
not been closed to reading) the MX node can read messages from the
streamlet without having to request a grant to access the
streamlet. The read messages can then be forwarded to client
devices that have subscribed to the channel. In various
implementations, messages read from streamlets are cached by MX
nodes so that MX nodes can reduce the number of times messages are
read from the streamlets.
[0029] In an implementation, an MX node can request a grant from
the channel manager that allows the MX node to store a block of
data into a streamlet on a particular Q node that stores streamlets
of the particular channel. Example streamlet grant request and
grant data structures are as follows:
TABLE-US-00001 StreamletGrantRequest = { ''channel'': string( )
''mode'': ''read'' | ''write'' "position": 0 }
StreamletGrantResponse = { ''streamlet-id'': ''abcdef82734987'',
''limit-size'': 2000000, # 2 megabytes max ''limit-msgs'': 5000, #
5 thousand messages max ''limit-life'': 4000, # the grant is valid
for 4 seconds "q-node": string( ) "position": 0 }
[0030] The StreamletGrantRequest data structure stores the name of
the stream channel and a mode indicating whether the MX node
intends on reading from or writing to the streamlet. The MX node
sends the StreamletGrantRequest to a channel manager node. The
channel manager node, in response, sends the MX node a
StreamletGrantResponse data structure. The StreamletGrantResponse
contains an identifier of the streamlet (streamlet-id), the maximum
size of the streamlet (limit-size), the maximum number of messages
that the streamlet can store (limit-msgs), the TTL (limit-life),
and an identifier of a Q node (q-node) on which the streamlet
resides. The StreamletGrantRequest and StreamletGrantResponse can
also have a position field that points to a position in a streamlet
(or a position in a channel) for reading from the streamlet.
[0031] A grant becomes invalid once the streamlet has closed. For
example, a streamlet is closed to reading and writing once the
streamlet's TTL has expired and or when the streamlet's storage is
full. When a grant becomes invalid, the MX node can request a new
grant from the channel manager to read from or write to a
streamlet. The new grant will reference a different streamlet and
will refer to the same or a different Q node depending on where the
new streamlet resides.
[0032] FIG. 3A is a data flow diagram of an example method 300 for
writing data to a streamlet in various embodiments. In FIG. 3A,
when an MX node (e.g., MX node 202) request to write to a streamlet
is granted by a channel manager (e.g., channel manager 214), as
described before, the MX node 202 establishes a Transmission
Control Protocol (TCP) connection with the Q node (e.g., Q node
208) identified in the grant response received from the channel
manager (302). A streamlet can be written concurrently by multiple
write grants (e.g., for messages published by multiple publishers).
Other types of connection protocols between the MX node 202 and the
Q node 208 are possible.
[0033] The MX node 202 sends a prepare-publish message with an
identifier of a streamlet that the MX node 202 wants to write to
the Q node 208 (304). The streamlet identifier and Q node
identifier can be provided by the channel manager in the write
grant as described earlier. The Q node 202 provides the message to
a handler 301 (e.g., a computing process running on the Q node 208)
for the identified streamlet (306). The handler 301 can send an
acknowledgment to the MX node 202 (308). After receiving the
acknowledgement, the MX node 202 starts writing (publishing)
messages (e.g., 310, 312, 314, and 318) to the handler 301, which
stores the received data in the identified streamlet. The handler
301 can also send acknowledgements (316, 320) to the MX node 202
for the received data. In some implementations, acknowledgements
can be piggy-backed or cumulative. For example, the handler 301 can
send an acknowledgement to the MX node 202 for every predetermined
amount of data received (e.g., for every 100 messages received) or
for every predetermined time period (e.g., for every one
millisecond). Other acknowledgement scheduling algorithms, such as
Nagle's algorithm, can be used.
[0034] If the streamlet can no longer accept published data (e.g.,
the streamlet is full), the handler 301 sends a
Negative-Acknowledgement (NAK) message (330) indicating a problem,
following by an EOF (end-of-file) message (332). In this way, the
handler 301 closes the association with the MX node 202 for the
publish grant. The MX node 202 can request a write grant for
another streamlet from a channel manager if the MX node 202 has
additional messages to store.
[0035] FIG. 3B is a data flow diagram of an example method 350 for
reading data from a streamlet in various embodiments. In FIG. 3B,
an MX node (e.g., MX node 204) sends a request to a channel manager
(e.g., channel manager 214) for reading a particular channel
starting from a particular message or time offset in the channel.
The channel manager returns a read grant to the MX node 204
including an identifier of a streamlet containing the particular
message, a position in the streamlet corresponding to the
particular message, and an identifier of a Q node (e.g., Q node
208) containing the particular streamlet. The MX node 204 then
establishes a TCP connection with the Q node 208 (352). Other types
of connection protocols between the MX node 204 and the Q node 208
are possible.
[0036] The MX node 204 then sends a subscribe message (354) to the
Q node 208 with the identifier of the streamlet in the Q node and
the position in the streamlet from which the MX node 204 wants to
read (356). The Q node 208 provides the subscribe message to a
handler 351 of the streamlet (356). The handler 351 can send an
acknowledgement to the MX node 204 (358). The handler 351 sends
messages (360, 364, 366), starting at the position in the
streamlet, to the MX node 204. In some implementations, the handler
351 can send all of the messages in the streamlet to the MX node
204. After sending the last message in a particular streamlet, the
handler 351 can send a notification of the last message to the MX
node 204. The MX node 204 can send to the channel manager another
request for another streamlet containing a next message in the
particular channel.
[0037] If the particular streamlet is closed (e.g., after its TTL
has expired), the handler 351 can send an unsubscribe message
(390), followed by an EOF message (392), to close the association
with the MX node 204 for the read grant. The MX node 204 can close
the association with the handler 351 when the MX node 204 moves to
another streamlet for messages in the particular channel (e.g., as
instructed by the channel manager). The MX node 204 can also close
the association with the handler 351 if the MX node 204 receives an
unsubscribe message from a corresponding client device.
[0038] In various implementations, a streamlet can be written into
and read from at the same time instance. For example, there can be
a valid read grant and a valid write grant at the same time
instance. In various implementations, a streamlet can be read
concurrently by multiple read grants (e.g., for channels subscribed
to by multiple publisher clients). The handler of the streamlet can
order messages from concurrent write grants based on, for example,
time-of-arrival, and store the messages based on the order. In this
way, messages published to a channel from multiple publisher
clients can be serialized and stored in a streamlet of the
channel.
[0039] In the messaging system 100, one or more C nodes (e.g., C
node 220) can offload data transfers from one or more Q nodes. For
example, if there are multiple MX nodes requesting streamlets from
Q nodes for a particular channel, the streamlets can be offloaded
and cached in one or more C nodes. The MX nodes (e.g., as
instructed by read grants from a channel manager) can read the
streamlets from the C nodes instead.
[0040] As described above, messages for a channel in the messaging
system 100 are ordered in a channel stream. A channel manager
(e.g., channel manager 214) splits the channel stream into
fixed-sized streamlets that each reside on a respective Q node. In
this way, storing a channel stream can be shared among many Q
nodes; each Q node stores a portion (one or more streamlets) of the
channel stream. More particularly, a streamlet can be stored in,
for example, registers and/or dynamic memory elements associated
with a computing process on a Q node, thus avoiding the need to
access persistent, slower storage devices such as hard disks. This
results in faster message access. The channel manager can also
balance load among Q nodes in the messaging system 100 by
monitoring respective workloads of the Q nodes and allocating
streamlets in a way that avoids overloading any one Q node.
[0041] In various implementations, a channel manager maintains a
list identifying each active streamlet, the respective Q node on
which the streamlet resides, an identification of the position of
the first message in the streamlet, and whether the streamlet is
closed for writing. In some implementations, Q nodes notify the
channel manager and any MX nodes that are publishing to a streamlet
that the streamlet is closed due to being full or when the
streamlet's TTL has expired. When a streamlet is closed, the
streamlet remains on the channel manager's list of active
streamlets until the streamlet's TTL has expired so that MX nodes
can continue to retrieve messages from the streamlet.
[0042] When an MX node requests a write grant for a given channel
and there is not a streamlet for the channel that can be written
to, the channel manager allocates a new streamlet on one of the Q
nodes and returns the identity of the streamlet and the Q node in
the StreamletGrantResponse to the MX node. Otherwise, the channel
manager returns the identity of the currently open for writing
streamlet and corresponding Q node in the StreamletGrantResponse to
the MX node. MX nodes can publish messages to the streamlet until
the streamlet is full or the streamlet's TTL has expired, after
which a new streamlet can be allocated by the channel manager.
[0043] When an MX node requests a read grant for a given channel
and there is not a streamlet for the channel that can be read from,
the channel manager allocates a new streamlet on one of the Q nodes
and returns the identity of the streamlet and the Q node in the
StreamletGrantResponse to the MX node. Otherwise, the channel
manager returns the identity of the streamlet and Q node that
contains the position from which the MX node wishes to read to the
MX node. The Q node can then begin sending messages to the MX node
from the streamlet beginning at the specified position until there
are no more messages in the streamlet to send. When a new message
is published to a streamlet, MX nodes that have subscribed to that
streamlet will receive the new message. If a streamlet's TTL has
expired, the handler process 351 sends an EOF message (392) to any
MX nodes that are subscribed to the streamlet.
[0044] As described earlier in reference to FIG. 2, the messaging
system 100 can include multiple channel managers (e.g., channel
managers 214, 215). Multiple channel managers provide resiliency
and prevent single point of failure. For instance, one channel
manager can replicate lists of streamlets and current grants it
maintains to another "slave" channel manager. As for another
example, multiple channel managers can coordinate operations
between them using distributed consensus protocols, such as, for
example, Paxos or Raft protocols.
[0045] FIG. 4A is a data flow diagram of an example method 400 for
publishing messages to a channel of a messaging system. In FIG. 4A,
publishers (e.g., publishers 402, 404, 406) publish messages to the
messaging system 100 described earlier in reference to FIG. 2. For
instance, publishers 402 respectively establish connections 411 and
send publish requests to the MX node 202. Publishers 404
respectively establish connections 413 and send publish requests to
the MX node 206. Publishers 406 respectively establish connections
415 and send publish requests to the MX node 204. Here, the MX
nodes can communicate (417) with a channel manager (e.g., channel
manager 214) and one or more Q nodes (e.g., Q nodes 212 and 208) in
the messaging system 100 via the internal network 218.
[0046] By way of illustration, each publish request (e.g., in JSON
key/value pairs) from a publisher to an MX node includes a channel
name and a message. The MX node (e.g., MX node 202) can assign the
message in the publish request to a distinct channel in the
messaging system 100 based on the channel name (e.g., "foo") of the
publish request. The MX node can confirm the assigned channel with
the channel manager 214. If the channel (specified in the subscribe
request) does not yet exist in the messaging system 100, the
channel manager can create and maintain a new channel in the
messaging system 100. For instance, the channel manager can
maintain a new channel by maintaining a list identifying each
active streamlet of the channel's stream, the respective Q node on
which the streamlet resides, and identification of the positions of
the first and last messages in the streamlet as described
earlier.
[0047] For messages of a particular channel, the MX node can store
the messages in one or more buffers or streamlets in the messaging
system 100. For instance, the MX node 202 receives from the
publishers 402 requests to publish messages M11, M12, M13, and M14
to a channel foo. The MX node 206 receives from the publishers 404
requests to publish messages M78 and M79 to the channel foo. The MX
node 204 receives from the publishers 406 requests to publish
messages M26, M27, M28, M29, M30, and M31 to the channel foo.
[0048] The MX nodes can identify one or more streamlets for storing
messages for the channel foo. As described earlier, each MX node
can request a write grant from the channel manager 214 that allows
the MX node to store the messages in a streamlet of the channel
foo. For instance, the MX node 202 receives a grant from the
channel manager 214 to write messages M11, M12, M13, and M14 to a
streamlet 4101 on the Q node 212. The MX node 206 receives a grant
from the channel manager 214 to write messages M78 and M79 to the
streamlet 4101. Here, the streamlet 4101 is the last streamlet of a
sequence of streamlets of the channel stream 430 storing messages
of the channel foo. The streamlet 4101 has messages 421 of the
channel foo that were previously stored in the streamlet 4101, but
is still open (e.g., the streamlet 4101 still has space for storing
more messages and the streamlet's TTL has not expired).
[0049] The MX node 202 can arrange the messages for the channel foo
based on the respective time that each of the messages 422 was
received by the MX node 202 (e.g., M11, M13, M14, M12) and store
the received messages as arranged in the streamlet 4101. That is,
the MX node 202 receives M11 first, followed by M13, M14, and M12.
Similarly, the MX node 206 can arrange the messages for the channel
foo based on their respective time that each of the messages 423
was received by the MX node 206 (e.g., M78, M79) and store the
received messages 423 as arranged in the streamlet 4101. Other
arrangements or ordering of the messages for the channel are
possible.
[0050] The MX node 202 (or MX node 206) can store the received
messages using the method for writing data to a streamlet described
earlier in reference to FIG. 3A, for example. In various
implementations, the MX node 202 (or MX node 206) can buffer (e.g.,
in a local data buffer) the received messages for the channel foo
and store the received messages in a streamlet for the channel foo
(e.g., streamlet 4101) when the buffered messages reach a
predetermined number or size (e.g., 100 messages) or when a
predetermined time (e.g., 50 milliseconds) has elapsed. For
example, the MX node 202 can store in the streamlet 100 messages at
a time or in 50 millisecond increments. Other acknowledgement
scheduling algorithms, such as Nagle's algorithm, can be used.
[0051] In various implementations, the Q node 212 (e.g., a handler)
stores the messages of the channel foo in the streamlet 4101 in the
order as arranged by the MX node 202 and MX node 206. The Q node
212 stores the messages of the channel foo in the streamlet 4101 in
the order the Q node 212 receives the messages. For instance,
assume that the Q node 212 receives message M78 (from the MX node
206) first, followed by messages M11 and M13 (from the MX node
202), M79 (from the MX node 206), and M14 and M12 (from the MX node
202). The Q node 212 stores in the streamlet 4101 the messages in
the order as received (e.g., M78, MI 1, M13, M79, M14, and MI 2)
immediately after the messages 421 that are already stored in the
streamlet 4101. In this way, messages published to the channel foo
from multiple publishers (e.g., MX nodes 402, 404) can be
serialized in a particular order and stored in the streamlet 4101
of the channel foo. Different subscribers that subscribe to the
channel foo will receive messages of the channel foo in the same
particular order, as will be described in more detail in reference
to FIG. 4B.
[0052] in the example of FIG. 4A, at a time instance after the
message M12 was stored in the streamlet 4101, the MX node 204
requests a grant from the channel manager 214 to write to the
channel foo. The channel manager 214 provides the MX node 204 a
grant to write messages to the streamlet 4101, as the streamlet
4101 is still open for writing. The MX node 204 arranges the
messages for the channel foo based on the respective time that each
message 424 was received by the MX node 204 (e.g., M26, M27, M31,
M29, M30, M28) and stores the messages as arranged for the channel
foo.
[0053] By way of illustration, assume that the message M26 is
stored to the last available position of the streamlet 4101. As the
streamlet 4101 is now full, the Q node 212 sends to the MX node 204
a NAK message, following by an EOF message, to close the
association with the MX node 204 for the write grant, as described
earlier in reference to FIG. 3A. The MX node 204 then requests
another write grant from the channel manager 214 for additional
messages (e.g., M27, M31, and so on) for the channel foo.
[0054] The channel manager 214 can monitor available Q nodes in the
messaging system 100 for their respective workloads (e.g., how many
streamlets are residing in each Q node). The channel manager 214
can allocate a streamlet for the write request from the MX node 204
such that overloading (e.g., too many streamlets or too many read
or write grants) can be avoided for any given Q node. For instance,
the channel manager 214 can identify a least loaded Q node in the
messaging system 100 and allocate a new streamlet on the least
loaded Q node for write requests from the MX node 204. In the
example of FIG. 4A, the channel manager 214 allocates a new
streamlet 4102 on the Q node 208 and provides a write grant to the
MX node 204 to write messages for the channel foo to the streamlet
4102. As shown in FIG. 4A, the Q node stores in the streamlet 4102
the messages from the MX node 204 in an order as arranged by the MX
node 204: M27, M31, M29, M30, and M28 (assuming that there is no
other concurrent write grants for the streamlet 4102 at the
moment).
[0055] When the channel manager 214 allocates a new streamlet
(e.g., streamlet 4102) for a request for a grant from an MX node
(e.g., MX node 204) to write to a channel (e.g., foo), the channel
manager 214 assigns to the streamlet its TTL, which will expire
after TTLs of other streamlets that are already in the channel's
stream. For instance, the channel manager 214 can assign to each
streamlet of the channel foo's channel stream a TTL of 3 minutes
when allocating the streamlet. That is, each streamlet will expire
3 minutes after it is allocated (created) by the channel manager
214. Since a new streamlet is allocated after a previous streamlet
is closed (e.g., filled entirely or expired), in this way, the
channel foo's channel stream includes streamlets that each expire
sequentially after the previous streamlet expires. For example, as
shown in an example channel stream 430 of the channel foo in FIG.
4A, streamlet 4098 and streamlets before 4098 (e.g., streamlet
4097) have expired (as indicated by the dotted-lined gray-out
boxes). Messages stored in these expired streamlets are not
available for reading for subscribers of the channel foo.
Streamlets 4099, 4100, 4101, and 4102 are still active (not
expired). The streamlets 4099, 4100, and 4101 are closed for
writing, but still are available for reading. The streamlet 4102 is
available for reading and writing, at the moment when the message
M28 was stored in the streamlet 4102. At a later time, the
streamlet 4099 will expire, following by the streamlets 4100, 4101,
and so on.
[0056] FIG. 4B is a data flow diagram of an example method 450 for
subscribing to a channel of a messaging system. In FIG. 4B, a
subscriber 480 establishes a connection 462 with an MX node 461 of
the messaging system 100. Subscriber 482 establishes a connection
463 with the MX node 461. Subscriber 485 establishes a connection
467 with an MX node 468 of the messaging system 100. Here, the MX
nodes 461 and 468 can respectively communicate (464) with the
channel manager 214 and one or more Q nodes in the messaging system
100 via the internal network 218.
[0057] A subscriber (e.g., subscriber 480) can subscribe to the
channel foo of the messaging system 100 by establishing a
connection 462 and sending a request for subscribing to messages of
the channel foo to an MX node (e.g., MX node 461). The request
(e.g., in JSON key/value pairs) can include a channel name, such
as, for example, "foo." When receiving the subscribe request, the
MX node 461 can send a request to the channel manager 214 for a
read grant for a streamlet in the channel foo's channel stream.
[0058] By way of illustration, assume that at the current moment
the channel foo's channel stream 431 includes active streamlets
4102, 4103, and 4104, as shown in FIG. 4B. The streamlets 4102 and
4103 each are full. The streamlet 4104 stores messages of the
channel foo, including the last message stored at a position 47731.
Streamlets 4101 and streamlets before 4101 are invalid, as their
respective TTLs have expired. Note that the messages M78, M11, M13,
M79, M14, M12, and M26 stored in the streamlet 4101, described
earlier in reference to FIG. 4A, are no longer available for
subscribers of the channel foo, since the streamlet 4101 is no
longer valid, as TTL of streamlet 4101 has expired. As described
earlier, each streamlet in the channel foo's channel stream has a
TTL of 3 minutes, thus only messages (as stored in streamlets of
the channel foo) that are published to the channel foo (i.e.,
stored into the channel's streamlets) no earlier than 3 minutes
from the current time can be available for subscribers of the
channel foo.
[0059] The MX node 461 can request a read grant for all available
messages in the channel foo, for example, when the subscriber 480
is a new subscriber to the channel foo. Based on the request, the
channel manager 214 provides the MX node 461 a read grant to the
streamlet 4102 (on the Q node 208) that is the earliest streamlet
in the active streamlets of the channel foo (e.g., the first in the
sequence of the active streamlets). The MX node 461 can retrieve
messages in the streamlet 4102 from the Q node 208, using the
method for reading data from a streamlet described earlier in
reference to FIG. 3B, for example. Note that the messages retrieved
from the streamlet 4102 maintain the same order as stored in the
streamlet 4102. However, other arrangements or ordering of the
messages in the streamlet are possible. In various implementations,
when providing messages stored in the streamlet 4102 to the MX node
461, the Q node 208 can buffer (e.g., in a local data buffer) the
messages and send the messages to the MX node 461 when the buffer
messages reach a predetermined number or size (e.g., 200 messages)
or a predetermined time (e.g., 50 milliseconds) has elapsed. For
instance, the Q node 208 can send the channel foo's messages (from
the streamlet 4102) to the MX node 461 200 messages at a time or in
50 millisecond increments. Other acknowledgement scheduling
algorithms, such as Nagle's algorithm, can be used.
[0060] After receiving the last message in the streamlet 4102, the
MX node 461 can send an acknowledgement to the Q node 208, and send
to the channel manager 214 another request (e.g., for a read grant)
for the next streamlet in the channel stream of the channel foo.
Based on the request, the channel manager 214 provides the MX node
461 a read grant to the streamlet 4103 (on Q node 472) that
logically follows the streamlet 4102 in the sequence of active
streamlets of the channel foo. The MX node 461 can retrieve
messages stored in the streamlet 4103 using the method for reading
data from a streamlet described earlier in reference to FIG. 3B,
until MX node 601 retrieves the last message stored in the
streamlet 4103. The MX node 461 can send to the channel manager 214
yet another request for a read grant for messages in the next
streamlet 4104 (on Q node 474). After receiving the read grant, the
MX node 461 retrieves message of the channel foo stored in the
streamlet 4104, until the last message at the position 47731 is
retrieved by MX node 461. Similarly, the MX node 468 can retrieve
messages from the streamlets 4102, 4103, and 4104 (as shown with
dotted arrows in FIG. 4B), and provide the messages to the
subscriber 485.
[0061] The MX node 461 can send the retrieved messages of the
channel foo to the subscriber 480 (via the connection 462) while
receiving the messages from the Q node 208, 472, or 474. In various
implementations, the MX node 461 can store the retrieved messages
in a local buffer. In this way, the retrieved messages can be
provided to another subscriber (e.g., subscriber 482) when the
other subscriber subscribes to the channel foo and requests the
channel's messages. The MX node 461 can remove messages stored in
the local buffer that each has a time of publication that has
exceeded a predetermined time period. For instance, the MX node 461
can remove messages stored in the local buffer with respective
times of publication exceeding 3 minutes. In some implementations,
the predetermined time period for keeping messages in the local
buffer on MX node 461 can be the same as or similar to the
time-to-live duration of a streamlet in the channel foo's channel
stream, since at a given moment, messages retrieved from the
channel's stream do not include the messages in streamlets having
respective time-to-lives that have already expired.
[0062] The messages retrieved from the channel stream 431 and sent
to the subscriber 480 (by the MX node 461) are arranged in the same
order as the messages were stored in the channel stream, although
other arrangements or ordering of the messages are possible. For
example, messages published to the channel foo are serialized and
stored in the streamlet 4102 in a particular order (e.g., M27, M31,
M29, M30, and so on), then stored subsequently in the streamlet
4103 and the streamlet 4104. The MX node 461 retrieves messages
from the channel stream 431 and provides the retrieved messages to
the subscriber 480 in the same order as the messages are stored in
the channel stream: M27, M31, M29, M30, and so on, followed by
ordered messages in the streamlet 4103, and followed by ordered
messages in the streamlet 4104.
[0063] Instead of retrieving all available messages in the channel
stream 431, the MX node 461 can request a read grant for messages
stored in the channel stream 431 starting from a message at
particular position (e.g., position 47202.) For example, the
position 47202 can correspond to an earlier time instance (e.g., 10
seconds before the current time) when the subscriber 480 was last
subscribing to the channel foo (e.g., via a connection to the MX
node 461 or another MX node of the messaging system 100). The MX
node 461 can send a request to the channel manager 214 for a read
grant for messages starting at the position 47202. Based on the
request, the channel manager 214 provides the MX node 461 a read
grant to the streamlet 4104 (on the Q node 474) and a position on
the streamlet 4104 that corresponds to the channel stream position
47202. The MX node 461 can retrieve messages in the streamlet 4104
starting from the provided position, and send the retrieved
messages to the subscriber 480.
[0064] As described above in reference to FIGS. 4A and 4B, messages
published to the channel foo are serialized and stored in the
channel's streamlets in a particular order. The channel manager 214
maintains the ordered sequence of streamlets as they are created
throughout their respective time-to-lives. Messages retrieved from
the streamlets by an MX node (e.g., MX node 461, or MX node 468)
and provided to a subscriber can be, in some implementations, in
the same order as the messages are stored in the ordered sequence
of streamlets. In this way, messages sent to different subscribers
(e.g., subscriber 480, subscriber 482, or subscriber 485) can be in
the same order (as the messages are stored in the streamlets),
regardless which MX nodes the subscribers are connected to.
[0065] In various implementations, a streamlet stores messages in a
set of blocks of messages. Each block stores a number of messages.
For instance, a block can store two hundred kilobytes of messages.
Each block has its own time-to-live, which can be shorter than the
time-to-live of the streamlet holding the block. Once a block's TTL
has expired, the block can be discarded from the streamlet holding
the block, as described in more detail below in reference to FIG.
4C.
[0066] FIG. 4C is an example data structure 490 for storing
messages of a channel of a messaging system. As described with the
channel foo in reference to FIGS. 4A and 4B1, assume that at the
current moment the channel foo's channel stream 432 includes active
streamlets 4104 and 4105. Streamlet 4103 and streamlets before
streamlet 4103 (e.g., streamlets 4101 and 4102) are invalid, as
their respective TTLs have expired. The streamlet 4104 has reach
maximum capacity (e.g., as determined by a corresponding write
grant) and is closed for additional message writes. The streamlet
4104 is available for message reads. The streamlet 4105 is open and
is available for message writes and reads.
[0067] By way of illustration, the streamlet 4104 (e.g., a
computing process running on the Q node 474 shown in FIG. 4B)
currently holds two blocks of messages. Block 494 holds messages
from channel positions 47301 to 47850. Block 495 holds messages
from channel positions 47851 to 48000. The streamlet 4105 (e.g., a
computing process running on another Q node in the messaging system
100) currently holds two blocks of messages. Block 496 holds
messages from channel positions 48001 to 48200. Block 497 holds
messages starting from channel position 48201, and still accepts
additional messages of the channel foo.
[0068] When the streamlet 4104 was created (e.g., by a write
grant), block 492 was created to store messages from channel
positions 47010 to 47100. Later on, after the block 492 had reached
its capacity, another block 493 was created to store messages
(e.g., from channel positions 47111 to 47300.) Blocks 494 and 495
were subsequently created to store additional messages. Afterwards,
the streamlet 4104 was closed for additional message writes, and
the streamlet 4105 was created with additional blocks for storing
additional messages of the channel foo.
[0069] In this example, the respective TTL's of blocks 492 and 493
have expired. The messages stored in these two blocks (from channel
positions 47010 to 47300) are no longer available for reading by
subscribers of the channel foo. The streamlet 4104 can discard
these two expired blocks. For example, the streamlet 4104 can
de-allocate the memory space for the blocks 492 and 493. The blocks
494 or 495 could become expired and be discarded by the streamlet
4104, before the streamlet 4104 itself becomes invalid.
Alternatively, streamlet 4104 itself could become invalid before
the blocks 494 or 495 become expired. For example, a streamlet can
hold one or more blocks of messages, or contain no block of
messages, depending on respective TTLs of the streamlet and
blocks.
[0070] A streamlet, or a computing process running on a Q node in
the messaging system 100, can create a block for storing messages
of a channel by allocating a certain size of memory space from the
Q node. The streamlet can receive, from an MX node in the messaging
system 100, one message at a time and store the received message in
the block. Alternatively, the MX node can assemble (e.g., buffer) a
group of messages and send the group of messages to the Q node. The
streamlet can allocate a block of memory space from the Q node and
store the group of messages in the block. The MX node can also
perform compression on the group of messages. For example, the MX
node can remove a common header from each message or performing
other suitable compression techniques.
[0071] Referring again to FIG. 2, in some examples, the systems and
methods described herein balance load among the Q nodes for one or
more channels. For example, when selecting a Q node to host a
streamlet for a channel, the channel manager 214 can select the Q
node based on its present workload (also referred to herein as
"load") and/or based on an expected workload the Q node will have
once the hosting begins. The workload of the Q node and other nodes
can be determined using load data that provides an indication of
how active or busy the Q nodes are at the current time and/or are
projected to be in the future. The load data for a given Q node can
include one or more load metrics, such as, for example, information
about the number of messages being handled or processed by the Q
node. In various implementations, the load data is or can include a
combination of two or more load metrics. For example, the
combination can be linear, non-linear, weighted, or un-weighted,
although other combinations are possible. In one example, the load
data can be a weighted combination of load metrics, with weights
for the combination determined through experimental measurements
and analysis of system performance. Linear regression or other
data-fitting techniques can be used to determine the weights and/or
the load metrics that have the greatest influence on workload and
system performance. In some instances, the load data can include
node-specific data representing loads on one or more Q nodes and/or
channel-specific data representing loads associated with one or
more channels. The load data can be or include, for example, a
combination (e.g., a weighted combination) of node-specific data
and/or channel-specific data.
[0072] In certain examples, the node-specific load data can include
the rate at which messages are being written to the Q node and/or
the rate at which messages are being delivered from the Q node. In
general, the higher the rate at which the Q node is sending and/or
receiving messages, the higher the workload is for the Q node. The
rate of transfer to or from the Q node can be compared with maximum
or threshold transfer rates for the Q node. The threshold transfer
rates can be determined statically, for example, by observing a
system configuration, such as a network interface (e.g., Ethernet)
device's capacity. Alternatively or additionally, the threshold
transfer rates can be determined dynamically, for example, by
observing the maximum transfer rates at which response latencies
remain at a pre-defined level. An initial threshold transfer rate
can also be determined experimentally, such as during benchmarking
of the system. In various instances, if the rate of transfer to
and/or from the Q node is at, near or exceeds the maximum available
or threshold transfer rate, the workload and/or the possible future
workload for the Q node can be considered high, such that the Q
node is less likely to be selected for hosting of additional
streamlets at that time. In some examples, message transfer rates
are measured in terms of the number of messages per time (e.g.,
messages per second) and/or the data transfer rate (e.g., bytes per
second).
[0073] In some instances, the node-specific load data can include
the number of streamlets or messages currently stored by the Q
nodes. The storage in the Q node can be compared with a maximum or
threshold storage value for the Q node. The threshold storage value
can be determined statically, for example, by observing the system
configuration and dedicating a portion of the system memory (e.g.,
RAM), such as 70%, 80%, 90% or other suitable percentage, to the
application. An initial threshold storage value can be determined
experimentally, such as during benchmarking of the system. In
general, when storage in a Q node is at, near or exceeds the
threshold storage value, the workload and/or possible future
workload can be considered high and/or the Q node may have limited
space for additional storage. In such cases, the Q node is less
likely to be selected at that time for storage of additional
streamlets. The number of messages stored by a Q node may be
measured, for example, in bytes or in number of messages.
[0074] Alternatively or additionally, node-specific load data for a
given Q node can include information about the number of channels
or channel portions (i.e., streamlets) currently being hosted or
processed by the Q node. The number of channels or channel portions
being hosted or processed by the Q node can be compared with a
maximum or threshold number of channels. If the number of channels
hosted by the Q node is at, near or exceeds the maximum number of
channels, the workload of the Q node and/or the possible future
workload can be considered high. In various instances, the maximum
number of channels can be limited by and/or determined from the
system memory and/or the CPU and network overhead of keeping or
maintaining a channel. An initial maximum number of channels can be
determined experimentally, such as during benchmarking of the
system. As messaging activity for a channel increases, the workload
for the Q node hosting the channel can be expected to increase. The
channel manager 214 can monitor trends in channel messaging
activity to predict how the hosting of streamlets will influence Q
node loads. If the expected workload associated with hosting a
streamlet will be too high for a Q node, the channel manager 214
can select a different Q node that has sufficient workload capacity
and/or available storage to host the streamlet.
[0075] In some instances, the node-specific load data for a Q node
is measured based on the number of MX nodes that have been given
read and/or write access to the Q node. The workload of a Q node
can increase as the number of MX nodes having read/write access to
the Q node increases. Additionally, the number of MX nodes having
read/write access to the Q node can provide an indication of the
possible future workload for the Q node. For example, when a large
number of MX nodes have read/write access to the Q node, the
potential for high message transfer rates exists, even though
current message transfer rates may not be high. In such cases, the
MX nodes can put higher demands on the Q node, as the activity
level on corresponding channels increases. The node-specific load
data for a Q node can include, in some instances, information
regarding (i) the number of received requests from MX nodes to
access streamlets stored on the Q node and/or (ii) the number of
permissions granted to the MX nodes to access the streamlets.
[0076] In general, the node-specific load data for a Q node can
include the processing rate for the Q node. A computation or
processing rate for the Q node can be calculated and compared with
a threshold or maximum processing value for the Q node. The
threshold processing (CPU) value can be, for example, between 30%
and 70% of a Q node CPU limit, to account for spikes, although
other threshold processing values are possible. In one example, the
threshold processing value can be determined by observing system
behavior under actual production load and determining safe
constraints, for example, by determining a level at which the
system becomes unstable, which may be indicated by oscillations in
traffic or processing rates. In one example, the threshold
processing value can be equal to one-half or one-third of the
processing rate corresponding to the onset of system instability,
although other threshold processing values are possible. When the
processing rate for the Q node is at, near, or exceeds the
threshold processing value, the workload for the Q node can be
considered high. With a high workload, the Q node is less likely to
be selected by the channel manager 214 to host a new streamlet.
[0077] in addition to monitoring the Q node workloads, the channel
manager 214 can also monitor rates of change in the workloads. The
node-specific load data can include, for example, an indication of
how the message transfer rates, message storage amounts, number of
channels hosted, number of MX node connections, the processing rate
for the Q node, and/or other load metrics are changing over time.
The rates of change can be or include, for example, a derivative or
slope associated with the load metrics. The rates of change can be
used to predict what the workload will be in the future for the Q
node. For example, the channel manager 214 can use the current
workload and the rate of change to extrapolate (e.g., linearly)
from the current workload to a predicted future workload.
[0078] In general, to determine if a current or future workload of
a Q node is high, the systems and methods (e.g., the channel
manager 214) can compare the current or future workload (e.g., a
message transfer rate or a storage rate) with a threshold value.
The threshold value can be, for example, a maximum value that
should not be exceeded, to avoid performance issues. In some
instances, the threshold value can be determined through
experimental observation and/or is chosen to be a workload above
which system performance is reduced or otherwise not optimal. The
workload for a Q node can be expressed as a raw load level or as a
percentage of the threshold value. In general, when the current or
predicted workload is at or near (or even exceeds) the threshold
value, the Q node can be considered overloaded and is less likely
to be selected to host a new streamlet.
[0079] Additionally or alternatively, the systems and methods
(e.g., the channel manager 214) can balance loads on the Q nodes by
considering channel-specific data. In general, channel-specific
data relates to information about a channel for which a new
streamlet will be hosted. Channel-specific data can include, for
example, the number of subscribers to a channel and/or the number
of publishers to the channel. If the number of subscribers and/or
publishers to the channel is high, an anticipated load associated
with a new streamlet for the channel can also be high. Likewise,
the channel-specific data can include a rate at which messages are
published to the channel. A high publication rate for a channel is
generally an indication that a workload associated with a new
streamlet for the channel will be high. In some examples, the
channel-specific data includes the number of interface nodes having
permission to access the channel. In general, when a large number
of interface nodes can access a channel, the expected workload for
the channel will be high, for example, due to more requests to read
from or write to the channel. Accordingly, channel-specific data
can allow the channel manager 214 to predict a workload associated
with a particular channel. The channel manager 214 can use the
predicted workload to determine how much work will be associated
with hosting a new streamlet for the channel. The channel manager
214 can then use the predicted workload to choose an appropriate Q
node for hosting the new streamlet. For example, if the predicted
workload for the streamlet is expected to be high, based on the
channel-specific data, the channel manager 214 can choose a Q node
having a workload that is low enough to handle the high workload
associated with the new streamlet.
[0080] In various examples, the node-specific data and/or the
channel-specific data can consider or include geographic location.
For example, if channel activity is primarily expected to be in a
particular geographic location (e.g., New Zealand), then the
channel manager 214 can select a Q node that resides in or near the
geographic location (e.g., in a New Zealand data center).
[0081] In some examples, the one or more Q nodes and/or the one or
more MX nodes provide the channel manager 214 with the load data,
including the node-specific data and/or the channel-specific data.
The Q nodes can be configured, for example, to monitor their
message transfer rates, messages storage amounts, MX node
connections, etc., and any associated rates of change, and provide
that information (e.g., node-specific data) to the channel manager
214. The same or similar node-specific information can be collected
by MX nodes and/or provided to the channel manager 214 by MX nodes.
The channel-specific data can likewise be collected by Q nodes
and/or MX nodes and sent to the channel manager 214. For example,
the Q nodes and/or the MX nodes can monitor one or more channels to
determine the number of subscribers, the number of publishers, the
rate of message publication, and/or the number of MX connections
for the channels.
[0082] In general, the channel manager 214 uses the load data
(i.e., node-specific data and/or channel-specific data) to balance
loads among the various Q nodes. For example, the channel manager
214 can use the load data to select the next Q node for hosting a
new streamlet. The next Q node can be chosen based on its current
workload or projected future workload, compared to other Q nodes in
the system. For example, when the channel manager 214 is selecting
a Q node to host a streamlet for a channel, the channel manager 214
can choose a Q node that has the lowest workload or the lowest
projected future workload among the available Q nodes. To predict
the future workload, the channel manager 214 can estimate an
additional workload associated with a future hosting task and add
the additional workload to the current workload for the Q node. The
channel manager 214 can also consider how many streamlets being
hosted by the Q node will expire in the future, thereby reducing
the Q node's workload.
[0083] In some cases, the channel manager 214 can predict a Q
node's workload at a future time as follows: future
workload=current workload+expected change in workload. The current
workload is generally a Q node's workload at a current time. The
expected change in workload is an expected difference between the
current workload and the expected workload at the future time. The
expected change in workload can be determined based on, for
example, the predicted increase in workload (e.g., due to hosting
new streamlets and/or increases in channel activity) and the
predicted decrease in workload (e.g., due to streamlet expiration
and/or decreases in channel activity).
[0084] in certain instances, the systems and methods (e.g., the
channel manager 214 and/or the Q nodes) can monitor the workloads
of the various Q nodes to determine when new streamlets need to be
opened or closed. For example, the channel manager 214 can decide
to close a streamlet on a Q node when a workload of the Q node is
getting high. The channel manager 214 can then open a new streamlet
for the corresponding channel on a different Q node, preferably
selected based on the load data and Q node workloads, as described
herein.
[0085] In various instances, when a first streamlet will be closed
and a second streamlet immediately following the first streamlet
will be opened, the channel manager 214 can open the second
streamlet on the Q node that is hosting the first streamlet. When
deciding to use the same Q node for the first and second
streamlets, the channel manager 214 can first confirm that the
workload of the Q node is below a threshold level, such that
opening the second streamlet will not overload the Q node.
Alternatively, if the workload of the Q node is above the threshold
level, the channel manager 214 can select a different Q node,
having a workload below the threshold level, to host the second
streamlet.
[0086] In general, when selecting Q nodes to host new streamlets,
the systems and methods can attempt to balance workloads among the
available Q nodes. When a new streamlet will be opened, for
example, the channel manager 214 can determine an expected workload
associated with hosting the new streamlet. The channel manager 214
can then select a Q node to host the new streamlet based on the
expected workload associated with hosting the streamlet. The Q node
can be selected such that workloads are distributed equally across
the Q nodes of the system. To determine workload inequality among
the Q nodes, the channel manager 214 can determine a standard
deviation of the workload distribution and select Q nodes for new
hosting tasks in an effort to minimize the standard deviation.
Other measurements of workload inequality can include, for example,
the difference between a maximum workload and a minimum workload
among the Q nodes, or the variance among the Q nodes. In general,
when selecting the next Q node for hosting a streamlet, the channel
manager 214 can make a Q node selection that reduces workload
inequality among the Q nodes.
[0087] In certain examples, the channel manager 214 can send a
request to a Q node to terminate hosting of a streamlet. The
request to terminate can be sent, for example, when a determination
is made that there are no subscribes to the channel associated with
the streamlet and/or when a time-to-live for the streamlet has
expired. In response to the request, the Q node can terminate the
hosting of the streamlet and inform the channel manager 214 that
the hosting has been terminated. Terminating the hosting of the
streamlet can include, for example, closing the streamlet to
further publication, closing the streamlet to further reading,
and/or deleting message data associated with the streamlet. A
decision to close a streamlet can be based on, for example, the
determination that the size of the streamlet exceeds a threshold
size, the determination that the age of the streamlet exceeds a
threshold age (e.g., a TTL), and/or the determination that the
hosting node has experienced a communication failure.
[0088] In some instances, an MX node informs the channel manager
214 about a request from a publisher to publish to a new channel.
In such a case, the channel manager 214 can determine that the
channel does not exist and, in response, can select a Q node to
host a streamlet for the new channel. The Q node selection can be
performed using the techniques described herein. The channel
manager 214 can select the same Q node or a different Q node to
host additional streamlets for the new channel (e.g., when a
preceding or youngest streamlet is closed to further
publication).
[0089] FIG. 5 is a flowchart of an example method for balancing
workload among Q nodes of a publish-subscribe system. The method
can be implemented using a channel manager, such as, for example,
the channel manager 214 of the messaging system 100. The method
begins by selecting (step 502), from a plurality of hosting nodes
(i.e., Q nodes) of a publish-subscribe system, a first hosting node
(i.e., a first Q node) to temporarily host a portion of a channel
of the publish-subscribe system. In certain instances, temporarily
hosting the channel portion includes temporarily storing one or
more messages published to the channel, and temporarily providing,
to a plurality of subscribers to the channel, access to the one or
more messages. The method also includes sending (step 504), to the
first hosting node of the publish-subscribe system, a request to
temporarily host the channel portion. A request to access the
channel portion is received (step 506) from an interface node
(i.e., an MX node) of the publish-subscribe system. Permission to
access the channel portion is granted (step 508) to the interface
node. In general, selecting the first hosting node to temporarily
host the channel portion includes selecting the first hosting node
from the plurality of hosting nodes based, at least in part, on
load data that includes node-specific data representing loads on
the plurality of hosting nodes and/or channel-specific data
representing a load associated with the channel.
[0090] Embodiments of the subject matter and the operations
described in this specification can be implemented in digital
electronic circuitry, or in computer software, firmware, or
hardware, including the structures disclosed in this specification
and their structural equivalents, or in combinations of one or more
of them. Embodiments of the subject matter described in this
specification can be implemented as one or more computer programs,
i.e., one or more modules of computer program instructions, encoded
on computer storage medium for execution by, or to control the
operation of, data processing apparatus. Alternatively or in
addition, the program instructions can be encoded on an
artificially-generated propagated signal, e.g., a machine-generated
electrical, optical, or electromagnetic signal, that is generated
to encode information for transmission to suitable receiver
apparatus for execution by a data processing apparatus. A computer
storage medium can be, or be included in, a computer-readable
storage device, a computer-readable storage substrate, a random or
serial access memory array or device, or a combination of one or
more of them. Moreover, while a computer storage medium is not a
propagated signal, a computer storage medium can be a source or
destination of computer program instructions encoded in an
artificially-generated propagated signal. The computer storage
medium can also be, or be included in, one or more separate
physical components or media (e.g., multiple CDs, disks, or other
storage devices).
[0091] The operations described in this specification can be
implemented as operations performed by a data processing apparatus
on data stored on one or more computer-readable storage devices or
received from other sources.
[0092] The term "data processing apparatus" encompasses all kinds
of apparatus, devices, and machines for processing data, including
by way of example a programmable processor, a computer, a system on
a chip, or multiple ones, or combinations, of the foregoing. The
apparatus can include special purpose logic circuitry, e.g., an
FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit). The apparatus can also
include, in addition to hardware, code that creates an execution
environment for the computer program in question, e.g., code that
constitutes processor firmware, a protocol stack, a database
management system, an operating system, a cross-platform runtime
environment, a virtual machine, or a combination of one or more of
them. The apparatus and execution environment can realize various
different computing model infrastructures, such as web services,
distributed computing and grid computing infrastructures.
[0093] A computer program (also known as a program, software,
software application, script, or code) can be written in any form
of programming language, including compiled or interpreted
languages, declarative or procedural languages, and it can be
deployed in any form, including as a stand-alone program or as a
module, component, subroutine, object, or other unit suitable for
use in a computing environment. A computer program may, but need
not, correspond to a file in a file system. A program can be stored
in a portion of a file that holds other programs or data (e.g., one
or more scripts stored in a markup language resource), in a single
file dedicated to the program in question, or in multiple
coordinated files (e.g., files that store one or more modules,
sub-programs, or portions of code). A computer program can be
deployed to be executed on one computer or on multiple computers
that are located at one site or distributed across multiple sites
and interconnected by a communication network.
[0094] The processes and logic flows described in this
specification can be performed by one or more programmable
processors executing one or more computer programs to perform
actions by operating on input data and generating output. The
processes and logic flows can also be performed by, and apparatus
can also be implemented as, special purpose logic circuitry, e.g.,
an FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit).
[0095] Processors suitable for the execution of a computer program
include, by way of example, both general and special purpose
microprocessors, and any one or more processors of any kind of
digital computer. Generally, a processor will receive instructions
and data from a read-only memory or a random access memory or both.
The essential elements of a computer are a processor for performing
actions in accordance with instructions and one or more memory
devices for storing instructions and data. Generally, a computer
will also include, or be operatively coupled to receive data from
or transfer data to, or both, one or more mass storage devices for
storing data, e.g., magnetic disks, magneto-optical disks, optical
disks, or solid state drives. However, a computer need not have
such devices. Moreover, a computer can be embedded in another
device, e.g., a mobile telephone, a personal digital assistant
(PDA), a mobile audio or video player, a game console, a Global
Positioning System (GPS) receiver, or a portable storage device
(e.g., a universal serial bus (USB) flash drive), to name just a
few. Devices suitable for storing computer program instructions and
data include all forms of non-volatile memory, media and memory
devices, including, by way of example, semiconductor memory
devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic
disks, e.g., internal hard disks or removable disks;
magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor
and the memory can be supplemented by, or incorporated in, special
purpose logic circuitry.
[0096] To provide for interaction with a user, embodiments of the
subject matter described in this specification can be implemented
on a computer having a display device, e.g., a CRT (cathode ray
tube) or LCD (liquid crystal display) monitor, for displaying
information to the user and a keyboard and a pointing device, e.g.,
a mouse, a trackball, a touchpad, or a stylus, by which the user
can provide input to the computer. Other kinds of devices can be
used to provide for interaction with a user as well; for example,
feedback provided to the user can be any form of sensory feedback,
e.g., visual feedback, auditory feedback, or tactile feedback; and
input from the user can be received in any form, including
acoustic, speech, or tactile input. In addition, a computer can
interact with a user by sending resources to and receiving
resources from a device that is used by the user; for example, by
sending web pages to a web browser on a user's client device in
response to requests received from the web browser.
[0097] Embodiments of the subject matter described in this
specification can be implemented in a computing system that
includes a back-end component, e.g., as a data server, or that
includes a middleware component, e.g., an application server, or
that includes a front-end component, e.g., a client computer having
a graphical user interface or a Web browser through which a user
can interact with an implementation of the subject matter described
in this specification, or any combination of one or more such
back-end, middleware, or front-end components. The components of
the system can be interconnected by any form or medium of digital
data communication, e.g., a communication network. Examples of
communication networks include a local area network ("LAN") and a
wide area network ("WAN"), an inter-network (e.g., the Internet),
and peer-to-peer networks (e.g., ad hoc peer-to-peer networks).
[0098] The computing system can include clients and servers. A
client and server are generally remote from each other and
typically interact through a communication network. The
relationship of client and server arises by virtue of computer
programs running on the respective computers and having a
client-server relationship to each other. In some embodiments, a
server transmits data (e.g., an HTML page) to a client device
(e.g., for purposes of displaying data to and receiving user input
from a user interacting with the client device). Data generated at
the client device (e.g., a result of the user interaction) can be
received from the client device at the server.
[0099] A system of one or more computers can be configured to
perform particular operations or actions by virtue of having
software, firmware, hardware, or a combination of them installed on
the system that in operation causes or cause the system to perform
the actions. One or more computer programs can be configured to
perform particular operations or actions by virtue of including
instructions that, when executed by data processing apparatus,
cause the apparatus to perform the actions.
[0100] While this specification contains many specific
implementation details, these should not be construed as
limitations on the scope of any inventions or of what may be
claimed, but rather as descriptions of features specific to
particular embodiments of particular inventions. Certain features
that are described in this specification in the context of separate
embodiments can also be implemented in combination in a single
embodiment. Conversely, various features that are described in the
context of a single embodiment can also be implemented in multiple
embodiments separately or in any suitable subcombination. Moreover,
although features may be described above as acting in certain
combinations and even initially claimed as such, one or more
features from a claimed combination can in some cases be excised
from the combination, and the claimed combination may be directed
to a subcombination or variation of a subcombination.
[0101] Similarly, while operations are depicted in the drawings in
a particular order, this should not be understood as requiring that
such operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed,
to achieve desirable results. In certain circumstances,
multitasking and parallel processing may be advantageous. Moreover,
the separation of various system components in the embodiments
described above should not be understood as requiring such
separation in all embodiments, and it should be understood that the
described program components and systems can generally be
integrated together in a single software product or packaged into
multiple software products.
[0102] Thus, particular embodiments of the subject matter have been
described. Other embodiments are within the scope of the following
claims. In some cases, the actions recited in the claims can be
performed in a different order and still achieve desirable results.
In addition, the processes depicted in the accompanying figures do
not necessarily require the particular order shown, or sequential
order, to achieve desirable results. In certain implementations,
multitasking and parallel processing may be advantageous.
* * * * *