U.S. patent application number 16/382090 was filed with the patent office on 2019-08-01 for data replication in scalable messaging system.
The applicant listed for this patent is Satori Worldwide, LLC. Invention is credited to Younes Hafri, Fredrik Erik Linder, Lev Walkin.
Application Number | 20190238637 16/382090 |
Document ID | / |
Family ID | 59791193 |
Filed Date | 2019-08-01 |
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United States Patent
Application |
20190238637 |
Kind Code |
A1 |
Hafri; Younes ; et
al. |
August 1, 2019 |
DATA REPLICATION IN SCALABLE MESSAGING SYSTEM
Abstract
A plurality of channels are maintained, wherein each channel
comprises a plurality of messages stored in one or more buffers,
wherein a first node stores a first copy of a first buffer for a
first channel of the plurality of channels, wherein each of a
plurality of secondary nodes stores a respective second copy of the
first buffer, and wherein at least one subscriber is subscribed to
messages of the first channel. A failure of the first node is
detected. One of the plurality of secondary nodes are identified as
a second node to access a second copy of the first buffer. The at
least one subscriber is redirected from the first node to the
second node and messages stored in the second copy on the second
node are retrieved for the at least one subscriber.
Inventors: |
Hafri; Younes; (Lausanne,
CH) ; 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: |
59791193 |
Appl. No.: |
16/382090 |
Filed: |
April 11, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15252989 |
Aug 31, 2016 |
10305981 |
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16382090 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 51/14 20130101;
H04L 41/0677 20130101; H04L 67/1095 20130101 |
International
Class: |
H04L 29/08 20060101
H04L029/08; H04L 12/24 20060101 H04L012/24; H04L 12/58 20060101
H04L012/58 |
Claims
1. A method, comprising: maintaining a plurality of channels,
wherein each channel comprises a plurality of messages stored in
one or more buffers, wherein a first node stores a first copy of a
first buffer for a first channel of the plurality of channels,
wherein each of a plurality of secondary nodes stores a respective
second copy of the first buffer, and wherein at least one
subscriber is subscribed to messages of the first channel;
detecting, by one or more computer processors, a failure of the
first node; identifying, by the one or more computer processors,
one of the plurality of secondary nodes as a second node to access
a second copy of the first buffer; redirecting, by the one or more
computer processors, the at least one subscriber from the first
node to the second node; and retrieving messages stored in the
second copy on the second node for the at least one subscriber.
2. The method of claim 1, wherein the messages for each channel are
stored in the one or more buffers according to an order.
3. The method of claim 1, wherein each buffer comprises a
respective time-to-live.
4. The method of claim 1, wherein identifying one of the plurality
of secondary nodes as the second node to access the second copy of
the first buffer comprises: selecting the second node based on a
respective workload for each node of the plurality of secondary
nodes.
5. The method of claim 1, comprising: redirecting at least one
publisher from the first node to the second node; and sending
messages from the at least one publisher to the second node for
storage in the second copy.
6. The method of claim 1, wherein the respective second copies of
the first buffer comprise a chain of copies including at least a
head copy and a tail copy.
7. The method of claim 6, comprising: forwarding messages stored in
a particular copy of the chain of copies to a next adjacent copy of
the chain of copies for storage, until messages in the head copy of
the chain of copies are stored in the tail copy of the chain of
copies.
8. The method of claim 1, wherein detecting the failure of the
first node comprises: detecting failure of the at least one
subscriber obtaining messages from the first copy.
9. The method of claim 1, wherein at least one publisher sends
messages of the first buffer to the first node for storage in the
first copy before being redirected to the second node.
10. The method of claim 1, wherein detecting the failure of the
first node comprises: detecting failure of at least one publisher
sending messages to the first node for storage in the first
copy.
11. A system, comprising: one or more computer processors
programmed to perform operations to: maintain a plurality of
channels, wherein each channel comprises a plurality of messages
stored in one or more buffers, wherein a first node stores a first
copy of a first buffer for a first channel of the plurality of
channels, wherein each of a plurality of secondary nodes stores a
respective second copy of the first buffer, and wherein at least
one subscriber is subscribed to messages of the first channel;
detect a failure of the first node; identify one of the plurality
of secondary nodes as a second node to access a second copy of the
first buffer; redirect the at least one subscriber from the first
node to the second node; and retrieve messages stored in the second
copy on the second node for the at least one subscriber.
12. The system of claim 11, wherein the messages for each channel
are stored in the one or more buffers according to an order.
13. The system of claim 11, wherein to identify one of the
plurality of secondary nodes as the second node to access the
second copy of the first buffer the one or more computer processors
are further to: select the second node based on a respective
workload for each node of the plurality of secondary nodes.
14. The system of claim 11, wherein the operations are further to:
redirect at least one publisher from the first node to the second
node; and send messages from the at least one publisher to the
second node for storage in the second copy.
15. The system of claim 11, wherein the respective second copies of
the first buffer comprise a chain of copies including at least a
head copy and a tail copy.
16. The system of claim 15, wherein the operations are further to:
forward messages stored in a particular copy of the chain of copies
to a next adjacent copy of the chain of copies for storage, until
messages in the head copy of the chain of copies are stored in the
tail copy of the chain of copies.
17. The system of claim 11, wherein to detect the failure of the
first node the one or more computer processors are further to:
detect failure of the at least one subscriber obtaining messages
from the first copy.
18. The system of claim 11, wherein at least one publisher sends
messages of the first buffer to the first node for storage in the
first copy before being redirected to the second node.
19. The system of claim 11, wherein to detect the failure of the
first node the one or more computer processors are further to:
detect failure of at least one publisher sending messages to the
first node for storage in the first copy.
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: maintain
a plurality of channels, wherein each channel comprises a plurality
of messages stored in one or more buffers, wherein a first node
stores a first copy of a first buffer for a first channel of the
plurality of channels, wherein each of a plurality of secondary
nodes stores a respective second copy of the first buffer, and
wherein at least one subscriber is subscribed to messages of the
first channel; detect a failure of the first node; identify one of
the plurality of secondary nodes as a second node to access a
second copy of the first buffer; redirect the at least one
subscriber from the first node to the second node; and retrieve
messages stored in the second copy on the second node for the at
least one subscriber.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/252,989, filed on Aug. 31, 2016, the entire
contents of which are incorporated by reference herein.
BACKGROUND
[0002] This specification relates to a data communication system
and, in particular, to a system that implements data replication in
a messaging system.
[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 which
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 methods that include the
actions of maintaining a plurality of channels, wherein each
channel comprises a plurality of messages stored in one or more
buffers, wherein a first node stores a first copy of a first buffer
for a first channel of the plurality of channels, wherein each of a
plurality of secondary nodes stores a respective second copy of the
first buffer, and wherein at least one subscriber is subscribed to
messages of the first channel. The method includes detecting, by
one or more computer processors, a failure of the first node and
identifying, by the one or more computer processors, one of the
plurality of secondary nodes as a second node to access a second
copy of the first buffer. The method further includes redirecting,
by the one or more computer processors, the at least one subscriber
from the first node to the second node; and retrieving messages
stored in the second copy on the second node for the at least one
subscriber. Other embodiments of this aspect include corresponding
systems, apparatus, and computer programs.
[0005] 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
[0006] FIG. 1A illustrates an example system that supports the
PubSub communication pattern.
[0007] FIG. 1B illustrates functional layers of software on an
example client device.
[0008] FIG. 2 is a diagram of an example messaging system.
[0009] FIG. 3A is a data flow diagram of an example method for
writing data to a streamlet.
[0010] FIG. 3B is a data flow diagram of an example method for
reading data from a streamlet.
[0011] FIG. 4A is a data flow diagram of an example method for
publishing messages to a channel of a messaging system.
[0012] FIG. 4B is a data flow diagram of an example method for
subscribing to a channel of a messaging system.
[0013] FIG. 4C is an example data structure for storing messages of
a channel of a messaging system.
[0014] FIG. 5A is a data flow diagram of an example method for
publishing and replicating messages of a messaging system.
[0015] FIG. 5B is a data flow diagram of an example method for
retrieving stored messages in a messaging system.
[0016] FIG. 5C is a data flow diagram of an example method for
repairing a chain of copies of data in a messaging system.
[0017] FIG. 5D is a data flow diagram of an example method for
repairing a chain of copies of data in a messaging system.
[0018] FIG. 6 is a flowchart of an example method for publishing
and subscribing messages for publishers and subscribers of a
messaging system.
DETAILED DESCRIPTION
[0019] FIG. 1A illustrates an example system 100 that supports the
PubSub communication pattern. Publishers (e.g., Publishers 1-N) can
publish messages to named channels (e.g., Channels 1-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-N) 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.
[0020] Depending on the configuration, a PubSub system can be
categorized as follows: [0021] One to One (1:1). In this
configuration there is one publisher and one subscriber per
channel. An example use case is private messaging. [0022] One to
Many (1:N). In this configuration there is one publisher and
multiple subscribers per channel. Example use cases are
broadcasting messages (e.g., stock prices). [0023] Many to Many
(M:N). In this configuration there are multiple publishers
publishing to a single channel. The messages are then delivered to
multiple subscribers. Example use cases are map applications.
[0024] 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 includes 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 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 subscribe, but not
publish, to the app1.system.notifications channel.
[0025] 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 includes 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.
[0026] 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.
[0027] FIG. 2 is a diagram of an example messaging system 100. The
messaging system 100 provides functionality for implementing PubSub
communication patterns. The messaging system 100 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
messaging system 100 includes multiplexer (MX) nodes 202, 204 and
206, queue (Q) 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 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 managers, is conducted over an internal
network 218. For example, 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 include a channel
stream. Messages can be ordered in a channel stream. For example,
the messages may be ordered 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, as will be discussed in
further detail below. The optional C nodes provide caching and load
removal from the Q nodes.
[0028] 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 202, 204 and 206 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.
[0029] In the example messaging system 100, a Q node (e.g., Q nodes
208, 210 and/or 212) 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. For
example, 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 example, 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.
[0030] 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. However, 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.
[0031] 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.
[0032] In implementations, 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 a
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 }
[0033] 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.
[0034] 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 a streamlet is closed to writing
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.
[0035] 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's (e.g., MX node 202) request to write to a
streamlet is granted by a channel manager (e.g., channel manager
214), 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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 208
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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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 loads 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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 200 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.
[0049] 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.
[0050] 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.
[0051] 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.)
[0052] 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.
[0053] 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.
[0054] 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, M11, M13, M79, M14, and M12)
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.
[0055] 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.
[0056] 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.
[0057] The channel manager 214 can monitor available Q nodes in the
messaging system 100 for the Q nodes 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
example, 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 208 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).
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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 the 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.
[0062] 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.
[0063] 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 461 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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 and/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.
[0068] 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.
[0069] 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 4B, 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 reached
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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] As described above, a streamlet (e.g., a data buffer)
residing on a Q node stores messages of a channel in the messaging
system 100. To prevent failure of the Q node (a single point
failure) causing messages to be lost, the messaging system 100 can
replicate messages on multiple Q nodes, as described in more detail
below.
[0075] FIG. 5A is a data flow diagram of an example method 500 for
publishing and replicating messages of the messaging system 100. As
described earlier in reference to FIG. 4A, the MX node 204 receives
messages (of the channel foo) from the publishers 406. The channel
manager 214 can instruct the MX node 204 (e.g., with a write grant)
to store the messages in the streamlet 4102 on the Q node 208. In
FIG. 5A, instead of storing the messages on a single node (e.g., Q
node 208), the channel manager 214 allocates multiple Q nodes to
store multiple copies of the streamlet 4102 on these Q nodes.
[0076] By way of illustration, the channel manager 214 allocates Q
nodes 208, 502, 504, and 506 in the messaging system 100 to store
copies of the streamlet 4102. The channel manager 214 instructs the
MX node 204 to transmit the messages for the channel foo (e.g.,
messages M27, M31, M29, M30, and M28) to the Q node 208 (512). A
computing process running on the Q node 208 stores the messages in
the first copy (copy #1) of the streamlet 4102. Instead of sending
an acknowledgement message to the MX node 204 after storing the
messages, the Q node 208 forwards the messages to the Q node 502
(514). A computing process running on the Q node 502 stores the
messages in another copy (copy #2) of the streamlet 4102.
Meanwhile, the Q node 502 forwards the messages to the Q node 504
(516). A computing process running on the Q node 504 stores the
messages in yet another copy (copy #3) of the streamlet 4102. The Q
node 504 also forwards the message to the Q node 506 (518). A
computing process running on the Q node 506 stores the messages in
yet another copy (copy #4) of the streamlet 4102. The Q node 506
can send an acknowledgement message to the MX node 204, indicating
that all the messages (M27, M31, M29, M30, and M28) have been
stored successfully in streamlet copies #1, #2, #3 and #4.
[0077] In some implementations, after successfully storing the last
copy (copy #4), the Q node 506 can send an acknowledgement to
upstream Q node 504, which in turns sends an acknowledgement to
upstream Q node 502, and so on, until the acknowledgement is sent
to the Q node 208 storing the first copy (copy #1). The Q node 208
can send an acknowledgement message to the MX node 204, indicating
that all messages have been stored successfully in the streamlet
4102 (i.e., in the copies #1, #2, #3 and #4).
[0078] In this way, four copies of the streamlet 4102 (and each
message in the streamlet) are stored in four different Q nodes.
Other numbers (e.g., two, three, five, or other suitable number) of
copies of a streamlet are also possible. In the present
illustration, the four copies form a chain of copies including a
head copy in the copy #1 and a tail copy in the copy #4. When a new
message is published to the streamlet 4102, the message is first
stored in the head copy (copy #1) on the Q node 208. The message is
then forwarded downstream to the next adjacent copy, the copy #2 on
the Q node 502 for storage, then to the copy #3 on the Q node 504
for storage, until the message is stored in the tail copy the copy
#4 on the Q node 506.
[0079] In addition to storing and forwarding by messages, the
computing processes running on Q nodes that store copies of a
streamlet can also store and forward messages by blocks of
messages, as described earlier in reference to FIG. 4C. For
instance, the computing process storing the copy #1 of the
streamlet 4102 on Q node 208 can allocate memory and store a block
of, for example, 200 kilobytes of messages (although other sizes of
blocks of messages are possible), and forward the block of messages
to the next adjacent copy (copy #2) of the chain for storage, and
so on, until the block messages is stored in the tail copy (copy
#4) on the Q node 506.
[0080] Messages of the streamlet 4102 can be retrieved and
delivered to a subscriber of the channel foo from one of the copies
of the streamlet 4102. FIG. 5B is a data flow diagram of an example
method 550 for retrieving stored messages in the messaging system
100. For instance, the subscriber 480 can send a request for
subscribing to messages of the channel to the MX node 461, as
described earlier in reference to FIG. 4B. The channel manager 214
can provide a read grant to the MX node 461 for one of the copies
of the streamlet 4102. The MX Node 461 can retrieve messages of the
streamlet 4102 from one of the Q nodes storing a copy of the
streamlet 4102, and provide the retrieved messages to the
subscriber 480. For instance, the MX node 461 can retrieve messages
from the copy #4 (the tail copy) stored on the Q node 506 (522). As
for another example, the MX node 461 can retrieve messages from the
copy #2 stored on the Q node 502 (524). In this way, the multiple
copies of a streamlet (e.g., copies #1, #2, #3, and #4 of the
streamlet 4102) provide replication and redundancy against failure
of one or more of Q nodes 208, 502, 504 or 506 of the messaging
system 100. In various implementations, the channel manager 214 can
balance workloads among the Q nodes storing copies of the streamlet
4102 by directing the MX node 461 (e.g., with a read grant) to a
particular Q node. For example, the channel manager 214 can direct
MX node 461 to a Q node having less current read and write grants
as compared to other Q nodes storing copies of the streamlet
4102.
[0081] In an example scenario, a Q node storing a particular copy
in a chain of copies of a streamlet may fail. For example, a
computing process on the Q node storing the particular copy may
freeze. Other failure modes of a Q node are possible. An MX node
can detect a failed node (e.g., from non-responsiveness of the
failed node) and report the failed node to a channel manager in the
messaging system 100 (e.g., channel manager 214). A peer Q node can
also detect a failed Q node and report the failed node to the
channel manager. For instance, an upstream Q node may detect a
failed downstream Q node when the downstream Q node is
non-responsive. For example, the downstream Q node may fail to
acknowledge a message storage request from the upstream Q node. It
is noted that failure of a Q node storing a copy of a particular
streamlet of a particular channel stream does not have to be for
publish or subscribe operations of the particular streamlet or of
the particular channel stream. Failure stemming from operations on
another streamlet or another channel stream can also alert a
channel manager about failure of a Q node in the messaging system
100.
[0082] When a Q node storing a particular copy in a chain of copies
of a streamlet fails, a channel manager in the messaging system 100
can repair the chain. For example, the messaging system 100 can
repair the chain by removing the failed node or by inserting a new
node for a new copy into the chain. FIG. 5C is a data flow diagram
of an example method 570 for repairing a chain of copies of a
streamlet in the messaging system 100. In FIG. 5C, for instance,
after detecting that the Q node 504 fails, the channel manager 214
can repair the chain of copies by redirecting messages intended to
be stored in the copy #3 of the streamlet 4102 on the Q node 502 to
the copy #4 of the streamlet 4102 on the Q node 506. In this
example, a message (or a block of messages) is first sent from the
MX node 204 to the Q node 208 for storage in the copy #1 of the
streamlet 4102 (572). The message then is forwarded to the Q node
502 for storage in the copy #2 of the streamlet 4102 (574). The
message is then forwarded to the Q node 506 for storage in the copy
#4 of the streamlet 4102 (576). The Q node 506 can send an
acknowledgement message to the channel manager 214 indicating that
the message has been stored successfully.
[0083] Here, a failed node can also be the node storing the head
copy or the tail copy of the chain of copies. For example, if the Q
node 208 fails, the channel manager 214 can instruct the MX node
204 first to send the message to the Q node 502 for storage in the
copy #2 of the streamlet 4102. The message is then forwarded to the
next adjacent copy in the chain for storage, until the message is
stored in the tail copy.
[0084] If the Q node 506 fails, the channel manager 214 can repair
the chain of copies of the streamlet 4102 such that the copy #3 on
the Q node 504 becomes the tail copy of the chain. A message is
first stored in the copy #1 on the Q node 208, then subsequently
stored in the copy #2 on the Q node 502, and the copy #3 on the Q
node 504. The Q node 504 then can send an acknowledgement message
to the channel manager 214 indicating that the message has been
stored successfully.
[0085] FIG. 5D is a data flow diagram of an example method 580 for
repairing a chain of copies of a streamlet in the message system
100. In FIG. 5D, the channel manager 214 replaces the failed Q node
504 by allocating a new Q node 508 to store a copy #5 of the chain
of copies of the streamlet 4102. In this example, the channel
manager 214 instructs the MX node 204 to send a message from the
publishers 406 to the Q node 208 for storage in the copy #1 of the
streamlet 4102 (582). The message is then forwarded to the Q node
502 for storage in the copy #2 of the streamlet 4102 (584). The
message is then forwarded to the Q node 508 for storage in the copy
#5 of the streamlet 4012 (586). The message is then forwarded to
the Q node 506 for storage in the copy #4 of the streamlet 4102
(588). The Q node 506 can send an acknowledgement message to the
channel manager 214 indicating that the message has been stored
successfully.
[0086] FIG. 6 is a flowchart of an example method 600 for
publishing and subscribing messages for publishers and subscribers,
respectively, of the system 100. The method can be implemented
using, for example, a channel manager (e.g., channel manager 214)
of the messaging system 100. The method begins by maintaining a
plurality of channels, each channel including ordered messages
stored in one or more buffers, each buffer having a respective
predetermined time-to-live and copies residing on respective nodes
(block 602). The method detects a failure of a first node of the
plurality of nodes (block 604), wherein the first node stores
respective first copies of first buffers for one or more first
channels, and wherein at least one subscriber is subscribed to
messages of the one or more first channels. For a first buffer with
a first copy residing on the first node, the method identifies any
other nodes as a second node storing a second copy of the first
buffer (block 606). The method redirects the at least one
subscriber and/or at least one publisher from the first node to the
second node (block 608). The method retrieves messages stored in
the second copy on the second node for the at least one subscriber
(block 610).
[0087] 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).
[0088] 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.
[0089] 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.
[0090] 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, procedural, or functional 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.
[0091] 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).
[0092] 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 smart phone, 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.
[0093] 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.
[0094] 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).
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] 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.
* * * * *