U.S. patent application number 11/322596 was filed with the patent office on 2007-07-05 for session handling based on shared session information.
Invention is credited to Christian Fleischer, Galin Galchev, Frank Kilian, Oliver Luik, Georgi Stanev.
Application Number | 20070156907 11/322596 |
Document ID | / |
Family ID | 37945100 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070156907 |
Kind Code |
A1 |
Galchev; Galin ; et
al. |
July 5, 2007 |
Session handling based on shared session information
Abstract
A connection manager and worker nodes of an application server
are both capable to access and control a shared memory session
table.
Inventors: |
Galchev; Galin; (Sofia,
BG) ; Fleischer; Christian; (Mannheim, DE) ;
Luik; Oliver; (Wiesloch, DE) ; Kilian; Frank;
(Mannheim, DE) ; Stanev; Georgi; (Sofia,
BG) |
Correspondence
Address: |
SAP/BLAKELY
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Family ID: |
37945100 |
Appl. No.: |
11/322596 |
Filed: |
December 30, 2005 |
Current U.S.
Class: |
709/227 |
Current CPC
Class: |
G06F 9/544 20130101;
G06F 2209/5016 20130101; H04L 67/141 20130101; G06F 9/5055
20130101; G06F 9/5033 20130101; G06F 9/5027 20130101 |
Class at
Publication: |
709/227 |
International
Class: |
G06F 15/16 20060101
G06F015/16 |
Claims
1. An apparatus comprising: a shared memory to store a session
table; a plurality of worker nodes coupled in communication with
the shared memory, each worker node capable to access and update an
entry in the session table with information about a session; and a
connection manager coupled in communication with the shared memory,
the connection manager to receive a request for the session, access
and update the entry in the session table with information about
the session, and to deposit the request in the shared memory where
a worker node can retrieve and process the request.
2. The apparatus of claim 1, wherein the information about the
session comprises a reference to a worker node selected to process
requests for the session.
3. The apparatus of claim 2, wherein the selected worker node to
retrieve the request from the shared memory and process the
request.
4. The apparatus of claim 1, wherein each of the plurality of
worker nodes is capable to allocate the entry in the session
table.
5. The apparatus of claim 4, wherein the worker node to allocate
the entry in the session table capable to initialize the entry.
6. The apparatus of claim 1, wherein each of the plurality of
worker nodes is capable to update the entry in the session
table.
7. The apparatus of claim 1, wherein each of the plurality of
worker nodes is capable to free the entry in the session table.
8. The apparatus of claim 1, wherein the worker node to free the
entry if no requests are pending for the session.
9. The apparatus of claim 5, wherein the connection manager to drop
the freed entry in the session table.
10. The apparatus of claim 1, wherein each of the plurality of
worker nodes capable to clean-up the entry in the session
table.
11. A method comprising: storing a session table in a shared
memory; accessing and updating an entry in the session table with
information about a session by one of a plurality of worker nodes
coupled in communication with the shared memory; and receiving at a
connection manager coupled in communication with the shared memory
a request for the session, accessing and updating the entry in the
session table with information about the session; depositing the
request in the shared memory; and retreiveing and processing the
request at a worker node.
12. The method of claim 11, further comprising selecting a worker
node to process requests for the session, wherein the information
about the session comprises a reference to the selected worker
node.
13. The method of claim 12, further comprising retrieving at the
selected worker node the request from the shared memory and
processing the request.
14. An article of manufacture, comprising: an electronically
accessible medium comprising instructions that when executed by a
processor, cause the processor to: store a session table in a
shared memory; access and update an entry in the session table with
information about a session by one of a plurality of worker nodes
coupled in communication with the shared memory; and receive at a
connection manager coupled in communication with the shared memory
a request for the session, access and update the entry in the
session table with information about the session; deposit the
request in the shared memory; and retreive and process the request
at a worker node.
15. The article of manufacture of claim 12, further comprising
instructions that cause the processor to select a worker node to
process requests for the session, wherein the information about the
session comprises a reference to the selected worker node.
16. The method of claim 15, further comprising instructions that
cause the processor to retrieve at the selected worker node the
request from the shared memory and process the request.
Description
FIELD OF INVENTION
[0001] The field of invention pertains generally to the software
arts; and, more specifically to an internetworking connection
manager comprising a dispatcher capable of receiving and load
balancing distribution of requests to worker processes in a
connection-oriented request/response communications
environment.
BACKGROUND
[0002] Even though standards-based application software (e.g., Java
based application software) has the potential to offer true
competition at the software supplier level, legacy proprietary
software has proven reliability, functionality and integration into
customer information systems (IS) infrastructures. Customers are
therefore placing operational dependency on standards-based
software technologies with caution. Not surprisingly, present day
application software servers tend to include instances of both
standard and proprietary software suites, and, often, "problems"
emerge in the operation of the newer standards-based software, or
interoperation and integration of the same with legacy software
applications.
[0003] The prior art application server 100 depicted in FIGS. 1a,b
provides a good example. FIG. 1a shows a prior art application
server 100 having both an ABAP legacy/proprietary software suite
103 and a Java J2EE standards-based software suite 104. A
connection manager 102 routes requests (e.g., HTTP requests, HTTPS
requests) associated with "sessions" between server 100 and
numerous clients (not shown in FIG. 1) conducted over a network
101. A "session" can be viewed as the back and forth communication
over a network 101 between computing systems (e.g., a particular
client and the server).
[0004] The back and forth communication typically involves a client
("client") sending a server 100 ("server") a "request" that the
server 100 interprets into some action to be performed by the
server 100. The server 100 then performs the action and if
appropriate returns a "response" to the client (e.g., a result of
the action). Often, a session will involve multiple, perhaps many,
requests and responses. A single session through its multiple
requests may invoke different application software programs.
[0005] For each client request that is received by the application
server's connection manager 102, the connection manager 102 decides
to which software suite 103, 104 the request is to be forwarded. If
the request is to be forwarded to the proprietary software suite
103, notification of the request is sent to a proprietary
dispatcher 105, and, the request itself is forwarded into a
request/response shared memory 106. The proprietary dispatcher 105
acts as a load balancer that decides which one of multiple
proprietary worker nodes 107.sub.1 through 107.sub.N are to
actually handle the request.
[0006] A worker node is a focal point for the performance of work.
In the context of an application server that responds to
client-server session requests, a worker node is a focal point for
executing application software and/or issuing application software
code for downloading to the client. The term "working process"
generally means an operating system (OS) process that is used for
the performance of work and is also understood to be a type of
worker node. For convenience, the term "worker node" is used
throughout the present discussion.
[0007] When the dispatcher 105 identifies a particular proprietary
worker node for handling the aforementioned request, the request is
transferred from the request/response shared memory 106 to the
identified worker node. The identified worker node processes the
request and writes the response to the request into the
request/response shared memory 106. The response is then
transferred from the request/response shared memory 106 to the
connection manager 102. The connection manager 102 sends the
response to the client via network 101.
[0008] Note that the request/response shared memory 106 is a memory
resource that each of worker nodes 107.sub.1 through 107.sub.L has
access to (as such, it is a "shared" memory resource). For any
request written into the request/response shared memory 106 by the
connection manager 102, the same request can be retrieved by any of
worker nodes 107.sub.1 through 107.sub.L. Likewise, any of worker
nodes 107.sub.1 through 107.sub.L can write a response into the
request/response shared memory 106 that can later be retrieved by
the connection manager 102. Thus the request/response shared memory
106 provides for the efficient transfer of request/response data
between the connection manager 102 and the multiple proprietary
worker nodes 107.sub.1 through 107.sub.L.
[0009] If the request is to be forwarded to the standards based
software suite 104, notification of the request is sent to the
dispatcher 108 that is associated with the standards based software
suite 104. As observed in FIG. 1a, the standards-based software
suite 104 is a Java based software suite (in particular, a Java 2
Enterprise Edition (J2EE) suite) that includes multiple worker
nodes 109.sub.1 through 109.sub.N.
[0010] A Java Virtual Machine is associated with each worker node
for executing the worker node's abstract application software code.
For each request, dispatcher 108 decides which one of the N worker
nodes is best able to handle the request (e.g., through a load
balancing algorithm). Because no shared memory structure exists
within the standards based software suite 104 for transferring
client session information between the connection manager 102 and
the worker nodes 109.sub.1 through 109.sub.N, separate internal
connections have to be established to send both notification of the
request and the request itself to the dispatcher 108 from
connection manager 102 for each worker node. The dispatcher 108
then forwards each request to its proper worker node.
[0011] FIG. 1b shows a more detailed depiction of the J2EE worker
nodes 109.sub.1 through 109.sub.N of the prior art system of FIG.
1a. Note that each worker node has its own associated virtual
machine, and, an extensive amount of concurrent application threads
are being executed per virtual machine. Specifically, there are X
concurrent application threads (112.sub.1 through 112.sub.X)
running on virtual machine 113; there are Y concurrent application
threads (212.sub.1 through 212.sub.Y) running on virtual machine
213; . . . and, there are Z concurrent application threads
(N12.sub.1 through N12.sub.Z) running on virtual machine N13;
where, each of X, Y and Z is a large number.
[0012] A virtual machine, as is well understood in the art, is an
abstract machine that converts (or "interprets") abstract code into
code that is understandable to a particular type of a hardware
platform (e.g., a particular type of processor). Because virtual
machines operate at the instruction level they tend to have
processor-like characteristics, and, therefore, can be viewed as
having their own associated memory. The memory used by a
functioning virtual machine is typically modeled as being local (or
"private") to the virtual machine. Hence, FIG. 1b shows local
memory 115, 215, . . . N15 allocated for each of virtual machines
113, 213, . . . N13 respectively.
[0013] Various problems exist with respect to the prior art
application server 100 of FIG. 1a. For example, the establishment
of connections between the connection manager and the J2EE
dispatcher to process a client session adds overhead/inefficiency
within the standards based software suite 104.
SUMMARY
[0014] A connection manager and worker nodes of an application
server are both capable to access and control a shared memory
session table.
FIGURES
[0015] The present invention is illustrated by way of example and
not limitation in the figures of the accompanying drawings, in
which like references indicate similar elements and in which:
[0016] FIG. 1a shows a prior art application server;
[0017] FIG. 1b shows a more detailed depiction of the J2EE worker
nodes of FIG. 1a;
[0018] FIG. 2 shows an improved application server;
[0019] FIGS. 3a and 3b show a session request and response
methodology that can be performed by the improved system of FIG.
2;
[0020] FIG. 4 shows a dispatching methodology;
[0021] FIG. 5 shows a methodology for rescuing sessions that have
been targeted for a failed worker node;
[0022] FIGS. 6a through 6c depict the rescue of a session whose
request notification was targeted for a failed worker node;
[0023] FIG. 7 shows different layers of a shared memory access
technology;
[0024] FIG. 8 shows a depiction of a shared closure based shared
memory system;
[0025] FIG. 9 shows a depiction of a computing system.
DETAILED DESCRIPTION
1.0 Overview
[0026] FIG. 2 shows the architecture of an improved application
server in accordance with embodiments of the invention.
[0027] Comparing FIGS. 1a and 2, firstly, note that the role of the
connection manager 202 has been enhanced to at least perform
dispatching 208 for the standards based software suite 204 (so as
to remove the additional connection overhead associated with the
prior art system's standards-based software suite dispatching
procedures).
[0028] Secondly, the connection manager is protocol independent. A
protocol handler can be plugged into the connection manager to
support any one of a number of protocols by which a request can be
conveyed to the connection manager. For example, handlers for
protocols such as the hypertext transfer protocol (HTTP), secure
HTTP (HTTPS), simple mail transfer protocol (SMTP), network news
transfer protocol (NNTP), Telnet, File Transfer Protocol (FTP),
Remote Method Invocation (RMI), P4 (a proprietary protocol used by
the assignee of the present invention), and T3, available from BEA
Systems, Inc., may be provided at the connection manager so that it
can receive a request conveyed from a client in accordance with any
of these protocols.
[0029] Third, the role of a shared memory has been expanded to at
least include: a) a first shared memory region 250 that supports
request/response data transfers not only for the proprietary suite
203 but also the standards based software suite 204; b) a second
shared memory region 260 that stores session objects having "low
level" session state information (i.e., information that pertains
to a request's substantive response such as the identity of a
specific servlet invoked through a particular web page); and, c) a
third shared memory region 270 that stores "high level" session
state information (i.e., information that pertains to the flow
management of a request/response pair within the application server
(e.g., the number of outstanding active requests for a
session)).
[0030] Third, request notification queues 212 Q1 through QM, one
queue for each of the worker nodes 209.sub.1 through 209.sub.M has
been implemented within the standards-based software suite 204. As
will be described in more detail below, the shared memory
structures 250, 260, 270 and request notification queues 212 help
implement a fast session fail over protection mechanism in which a
session that is assigned to a first worker node can be readily
transferred to a second worker node upon the failure of the first
worker node.
[0031] Shared memory is memory whose stored content can be reached
by multiple worker nodes. Here, the contents of the shared memory
region 250 can be reached by each of worker nodes in 207 and 209.
Additionally, the contents of shared memory regions 260 and 270 can
be reached by each of worker nodes 209.sub.1 through 209.sub.M.
Different types of shared memory technologies may be utilized
within the application server 200 and yet still be deemed as being
a shared memory structure. For example, shared memory region 250
may be implemented within a "connection" oriented shared memory
technology while shared memory region 260 may be implemented with a
"shared closure" oriented shared memory technology. A more thorough
discussion of these two different types of shared memory
implementations is provided in more detail below in section 5.0
entitled "Implementation Embodiment of Request/Response Shared
Memory" and section 6.0 entitled "Implementation Embodiment of
Shared Closure Based Shared Memory".
[0032] The connection oriented request/response shared memory
region 250 effectively implements a transport mechanism for
request/response data between the connection manager and the worker
nodes. That is, because the connection manager is communicatively
coupled to the shared memory, and because the shared memory is
accessible to each worker node, the request/response shared memory
250--at perhaps its broadest level of abstraction--is a mechanism
for transporting request/response data between the connection
manager and the applicable worker node(s) for normal operation of
sessions (i.e., no worker node failure) as well as those sessions
affected by a worker node crash.
[0033] Although the enhancements of the application server 200 of
FIG. 2 have been directed to improving the reliability of a
combined ABAP/J2EE application server, it is believed that
architectural features and methodologies described in more detail
further below can be more generally applied to various forms of
computing systems that manage communicative sessions, whether or
not such computing systems contain different types of application
software suites, and whether any such application software suites
are standards-based or proprietary. Moreover, it is believed that
such architectural features and methodologies are generally
applicable regardless of any particular type of shared memory
technology employed.
[0034] In operation, the connection manager 202 forwards actual
request data to the first shared memory region 250
(request/response shared memory 250) regardless of whether the
request is to be processed by one of the proprietary worker nodes
207 or one of the standards based worker nodes 204. Likewise, the
connection manager 202 receives response data for a request from
the request/response shared memory 250 whether a proprietary worker
node or a standards based worker node generates the response.
[0035] With the exception of having to share the request/response
shared memory 250 with the worker nodes 209 of the standards-based
software suite 204, the operation of the proprietary software suite
203 is essentially the same as that described in the background, in
one embodiment of the invention. That is, the connection manager
202 forwards request notifications to the proprietary dispatcher
205 and forwards the actual requests to the request/response shared
memory 250. The proprietary dispatcher 205 then identifies which
one of the proprietary worker nodes 207 is to handle the request.
The identified worker node subsequently retrieves the request from
the request/response shared memory 250, processes the request and
writes the response into the request/response shared memory 250.
The response is then forwarded from the request/response shared
memory 250 to the connection manager 202 which then forwards the
response to the client via network 201.
[0036] In an alternative embodiment, the ABAP dispatcher 205 is
integrated into the connection manager, just as the J2EE dispatcher
208. Indeed, it is contemplated that a single dispatcher may
encompass the functionality of both dispatchers 205 and 208. In the
case where the dispatcher 205 is integrated into the connection
manager 202, the connection manager identifies which one of the
proprietary worker nodes 207 is to handle a request and via its
integrated dispatcher capabilities, forwards the request to the
request/response shared memory 250. The identified worker node
subsequently retrieves the request from the request/response shared
memory 250, processes the request and writes the response into the
request/response shared memory 250. The response is then forwarded
from the request/response shared memory 250 to the connection
manager 202 who forwards the response to the client via network
201.
2.0 Processing a Request Received over a Session
[0037] FIGS. 3a and 3b show an improved session handling flow that
is used within the standards based software suite 204 of the
improved application server 200 of FIG. 2. According to this flow,
after the connection manager 302 receives a request from network
301 and determines that the request should be handled by the
standards-based software suite, the session to which the request
belongs is identified (or the request is identified as being the
first request of a new session). Here, the connection manager 302
determines the existing session to which the request belongs or
that the request is from a new session through well understood
techniques (e.g., through a session identifier found in the header
of the received request or a URL path found in the header of the
received request).
[0038] Then, the dispatcher 308 for the standards-based software
suite is invoked. One possible dispatching algorithm that is
executed by the dispatcher 308 is described in more detail further
below in Section 3.0 entitled "Dispatching Algorithm". For purposes
of the present discussion it is sufficient to realize that the
dispatcher 308: 1) accesses and updates at 1 "high level" state
information 370.sub.1 for the request's session in the shared
memory session table 370 (hereinafter, referred to as session table
370); 2) determines which one 309 of the M worker nodes should
handle the newly arrived request; and 3) submits at 2 the request
322.sub.1 into the request/response shared memory 350 and submits
at 3 a request notification 320.sub.1 for the request 322.sub.1
into a request notification queue Q1 that is associated with the
worker node 309 selected by the dispatching algorithm. For ease of
drawing, FIGS. 3a and 3b only depict the worker node 309 that has
been selected by the dispatcher 308 to handle the request.
[0039] In an embodiment, there is an entry in the session table 370
for each session being supported by the M worker nodes. If the
received request is for a new session (i.e., the received request
is the first request of the session), the dispatcher process 308
will create at 1 a new entry 370.sub.1 in the session table 370 for
the new session and assign at 2 one of the M worker nodes to handle
the session based on a load balancing algorithm. By contrast, if
the received request pertains to an already existing session, the
dispatcher process 308 will access at 1 the already existing entry
370.sub.1 for the session and use the information therein to
effectively determine the proper worker node to handle the request
as well as update at 1 the session table entry 370.sub.1. In an
embodiment, as will be described in detail further below in Section
3.0, in the case of an already existing session, the determination
of the proper worker node may or may not involve the execution of a
load balancing algorithm.
[0040] In an embodiment, the following items are associated with
each session table entry 370: 1) a "key" used to access the session
table entry 370.sub.1 itself (e.g., session key "SK1"); 2) an
active request count (ARC) that identifies the total number of
requests for the session that have been received from network 301
but for which a response has not yet been generated by a worker
node; 3) an identifier of the worker node 309 that is currently
assigned to handle the session's requests (e.g., "Pr_Idx", which,
in an embodiment, is the index in the process table of the worker
node that is currently assigned to handle the session's requests);
and, 4) some form of identification of the request notification
queue (Q1) that provides request notifications to the worker node
309 identified in 3) above.
[0041] In a further embodiment, each entry in the session table 370
further includes: 1) a flag that identifies the session's type
(e.g., as described in more detail further below in Section 4.1,
the flag can indicate a "distributed" session, a "sticky" session,
or a "corrupted" session); 2) a timeout value that indicates the
maximum amount of time a request can remain outstanding, that is,
waiting for a response; 3) the total number of requests that have
been received for the session; 4) the time at which the session
entry was created; and, 5) the time at which the session entry was
last used.
[0042] For each request, whether a first request of a new session
or a later request for an already established session, the
dispatcher's dispatching algorithm 308 increments the ARC value and
at 3 places a "request notification" RN_1 320.sub.1, into the
request notification queue Q1 that feeds request notifications to
the worker node 309 that is to handle the session. The request
notification RN_1 contains both a pointer to the request data RQD_1
322.sub.1 in the request/response shared memory and the session key
SK1 in the session table entry for the session.
[0043] The pointer to the request data in request/response shared
memory 350 is generated by that portion of the connection manager
302 that stores the request data RQD_1 322.sub.1 into shared memory
350 and is provided to the dispatcher 308. The pointer is used by
the worker node 309 to fetch the request data RQD_1 322.sub.1 from
the request/response shared memory 350, and, therefore, the term
"pointer" should be understood to mean any data structure that can
be used to locate and fetch the request data. The worker node 309
uses the session key (or some other data structure in the request
notification RN_1 that can be used to access the session table
entry 370.sub.1 for the session) to access and decrement the ARC
counter to indicate the worker node 309 has fully responded to the
request for that session.
[0044] As will be described in more detail below in section 5.0
entitled "Implementation Embodiment of Request/Response Shared
Memory", according to a particular implementation, the
request/response shared memory 350 is connection based. Here, a
connection is established between the targeted (assigned) worker
node 309 and the connection manager 302 through the
request/response shared memory 350 for each request/response cycle
that is executed in furtherance of a particular session; and, a
handle for a particular connection is used to retrieve a particular
request from the request/response shared memory 350 for a
particular request/response cycle. According to this
implementation, the pointer in the request notification RN is the
"handle" for the shared memory 350 connection that is used to fetch
request data RQD_1 322.sub.1. (The connection between the
connection manager and the worker node established to handle a
request/response cycle should not be confused with a network
connection between a client over network 101 that is the source of
the request and the application server).
[0045] In the case of a first request for a new session, the
dispatcher 308 determines the worker node to be assigned to handle
the session (e.g., with the assistance of a load balancing
algorithm) and places the identity of the worker node's request
notification queue (Q1) into a newly created session table entry
370.sub.1 for the session along with some form of identification of
the worker node itself (e.g., "Pr_Idx", the index in the process
table of the worker node that is currently assigned to handle the
session's requests). For already existing sessions, the dispatcher
308 simply refers to the identity of the request notification queue
(Q1) in the session's session table entry 370.sub.1 in order to
determine into which request notification queue the request
notification RN should be entered.
[0046] Continuing then with a description of the present example,
with the appropriate worker node 309 being identified by the
dispatcher 308, the dispatcher 308 continues with the submission at
2 of the request RQD_1 322.sub.1 into the request/response shared
memory 350 and the entry at 3 of a request notification RN_1
320.sub.1 into the queue Q1 that has been established to supply
request notifications to worker node 309. The request notification
RN_1 320.sub.1 sits in its request notification queue Q1 until the
targeted worker node 309 foresees an ability (or has the ability)
to process the corresponding request 322.sub.1. Recall that the
request notification RN_1 320.sub.1 includes a pointer to the
request data itself RQD_1 322.sub.1 as well as a data structure
that can be used to access the entry 370.sub.1 in the session table
(e.g., the session key SK1).
[0047] Comparing FIGS. 2 and 3a, note that with respect to FIG. 2 a
separate request notification queue is implemented for each worker
node (that is, there are M queues, Q1 through QM, for the M worker
nodes 209.sub.1 through 209.sub.M, respectively). As will be
described in more detail below with respect to FIGS. 5a,b and 6a-c,
having a request notification queue for each worker node allows for
the "rescue" of a session whose request notification(s) have been
entered into the request notification queue of a particular worker
node that fails ("crashes") before the request notification(s)
could be serviced from the request notification queue.
[0048] When the targeted worker node 309 foresees an ability to
process the request 322.sub.1, it looks to its request notification
queue Q1 and retrieves at 4 the request notification RN_1 320.sub.1
from the request notification queue Q1. FIG. 3a shows the targeted
worker node 309 as having the request notification RN_1 320.sub.2
to reflect the state of the worker node after this retrieval at 4.
Recalling that the request notification RN_1 320.sub.1 includes a
pointer to the actual request RQD_1 322.sub.1 within the
request/response shared memory 350, the targeted worker node 309
subsequently retrieves at 5 the appropriate request RQD_1 322.sub.1
from the request/response shared memory 350. FIG. 3a shows the
targeted worker node 309 as having the request RQD_1 322.sub.2 to
reflect the state of the worker node after this retrieval at 5. In
an embodiment where the request/response shared memory is
connection oriented, the pointer to RQD_1 322.sub.1 is a "handle"
that the worker node 309 uses to establish a connection with the
connection manager 302 and then read at 5 the request RQD_1
322.sub.1 from the request/response shared memory.
[0049] The targeted worker node 309 also assumes control of one or
more "session" objects S1 323.sub.2 used to persist "low level"
session data. Low level session data pertains to the request's
substantive response rather than its routing through the
application server. If the request is the first request for a new
session, the targeted worker node 309 creates the session object(s)
S1 323.sub.2 for the session; or, if the request is a later request
of an existing session, the targeted worker node 309 retrieves at 6
previously stored session object(s) S1 323.sub.1 from the "shared
closure" memory region 360 into the targeted worker node 323.sub.2.
The session object(s) S1 323.sub.1 may be implemented as a number
of objects that correspond to a "shared closure". A discussion of
shared closures and an implementation of a shared closure memory
region 360 is provided in more detail further below in section 6.0
entitled "Implementation Embodiment of Shared Closure Based Shared
Memory"
[0050] With respect to the handling of a new session, the targeted
worker node 309 generates a unique identifier for the session
object(s) S1 323.sub.1 according to some scheme. In an embodiment,
the scheme involves a random component and an identifier of the
targeted worker node itself 309. Moreover, information sufficient
to identify a session uniquely (e.g., a sessionid parameter from a
cookie that is stored in the client's browser or the URL path of
the request) is found in the header of the request RQD_1 322.sub.2
whether the request is the first request of a new session or a
later requests of an existing session. This information can then be
used to fetch the proper session object(s) S1 323.sub.1 for the
session.
[0051] FIG. 3b depicts the remainder of the session handling
process. With the targeted worker node 309 having the request RQD_1
322.sub.2 and low level session state information via session
object(s) S1 323.sub.2, the request is processed by the targeted
worker node 309 resulting in the production of a response 324 that
is to be sent back to the client. The worker node 309 writes at 7
the response 324 into the response/request shared memory 350; and,
if a change to the low level session state information was made
over the course of generating the response, the worker node 309
writes at 8 updated session object(s) into the shared closure
memory 360. Lastly, the worker node 309 decrements at 9 the ARC
value (311) in the session table entry 370.sub.1 to reflect the
fact that the response process has been fully executed from the
worker node's perspective and that the request has been satisfied.
Here, recall that a segment of the request notification RN_1
320.sub.2 (e.g., the session key SK1) can be used to find a "match"
to the correct entry 370.sub.1 in the session table 370 in order to
decrement the ARC value for the session.
[0052] In reviewing the ARC value across FIGS. 3a and 3b, note that
it represents how many requests for the session the connection
manager has received from network 301 but for which no response has
yet been generated by a worker node. In the example provided with
reference to FIGS. 3a and 3b only one request is outstanding at any
one point in time, hence, the ARC value never exceeds a value of 1.
Conceivably, multiple requests for the same session could be
received from network 301 prior to any responses being generated.
In such a case the ARC value will indicate the number of requests
that is queued or is currently being processed by one or more
worker nodes but for which no response has been generated.
[0053] After the response 324 is written at 7 into the
request/response shared memory 350, it is retrieved at 10 into the
connection manager 302 which then sends it to the client over
network 301.
[0054] In a further embodiment, a single session can generate
multiple "client connections" over its lifespan, where each client
connection corresponds to a discrete time/action period over which
the client engages with the server. Different client connections
can therefore be setup and torn down between the client and the
server over the course of engagement of an entire session. Here,
depending on the type of client session, for example in the case of
a "distributed" session (described in more detail further below),
the dispatcher 308 may decide that a change should be made with
respect to the worker node that is assigned to handle the session.
If such a change is to be made the dispatcher 308 performs the
following within the entry 370.sub.1 for the session: 1) replaces
the identity of the "old" worker node with the identity of the
"new" worker node (e.g., a "new" Pr_Idx value will replace an "old"
Pr_Idx value); and, 2) replaces the identification of the request
notification queue for the "old" worker node, e.g., with an
identification of the request notification queue for the "new"
worker node.
[0055] In another embodiment, over the course a single session and
perhaps during the existence of a single client connection, the
client may engage with different worker node applications. Here, a
different entry in the session table can be entered for each
application that is invoked during the session. As such, the level
of granularity of a session's management is drilled further down to
each application rather than just the session as a whole. A
"session key" (SK1) is therefore generated for each application
that is invoked during the session. In an embodiment, the session
key has two parts: a first part that identifies the session and a
second part that identifies the application (e.g., numerically
through a hashing function).
[0056] In the application level dispatching embodiment, a client
request is received by the connection manager 302, which then
queries an alias table for an alias (.e.g., short name) of an
application executing on a worker node to handle the request. Given
the alias, the connection manager performs a hashing function to
generate and alias ID which is combined with a session ID from the
request to form a session key, if the there is an existing session
associated with the request. If there is no existing session, the
alias ID may be combined with a session ID having a value of nil,
or simply the alias ID is used as the session key.
[0057] Given the session key, the session table is searched for an
existing session table entry having the same session key, and if
not found, a new session table entry is created. In this manner,
multiple entries may be made in the session table for the same
session, but different applications. Each session table entry
specifies not only the worker node to handle the request, but the
particular application executing on the worker node to handle the
request.
[0058] Continuing on, the connection manager places the request in
the request/response shared memory, and enters the corresponding
request notification in the request notification queue associate
with the worker node on which the application is executing, in the
same manner as described above.
3.0 Dispatching Algorithm
[0059] Recall from the discussions of FIGS. 2 and 3a,b that the
connection manager 202, 302 includes a dispatcher 208, 308 that
executes a dispatching algorithm for requests that are to be
processed by any of the M worker nodes 209. In one embodiment of
the invention, the connection manager includes ABAP dispatcher 205
as well, and executes a dispatching algorithm for requests that are
to be processed by any of the N worker nodes 207. In an alternative
embodiment, the dispatchers 205 and 208 may be combined into one
dispatcher in connection manager 202, in which case the combined
dispatcher executes a dispatching algorithm for requests that are
to be processed by any of the N worker nodes 207 or M worker nodes
209.
[0060] FIG. 4 shows an embodiment 400 of a dispatching algorithm
that can be executed by the connection manager. The dispatching
algorithm 400 of FIG. 4 contemplates the existence of two types of
sessions: 1) "distributable"; and, 2) "sticky".
[0061] A distributable session is a session that permits the
handling of its requests by different worker nodes over the course
of its regular operation (i.e., no worker node crash). A sticky
session is a session whose requests are handled by only one worker
node over the normal course (i.e., no worker node crash) of its
operation. That is, the sticky session "sticks" to the one worker
node. According to an implementation, each received request that is
to be processed by any of worker nodes 209 is dispatched according
to the process 400 of FIG. 4.
[0062] Before execution of the dispatching process 400, the
connection manager 202, 302 will determine: 1) whether the request
is the first request for a new session or is a subsequent request
for an already existing session (e.g., in the case of the former,
there is no "sessionID" from the client's browser's cookie in the
header of the request, in the later case there is a such a
"sessionID"); and, 2) the type of session associated with the
request (e.g., sticky or distributable). In an embodiment, the
default session type is "distributable" but can be changed to
"sticky", for example, by the worker node that is presently
responsible for handling the session.
[0063] At 401, if the request is not a first request for a new
session, whether the received request corresponds to a sticky or
distributable session is determined by reference to the session
table entry for the session. If it is determined at 402 that the
session is a sticky session, the request is assigned to the worker
node that has been assigned at 405 to handle the session to which
the request belongs. According to the embodiment described with
respect to FIGS. 3a,b, the identity of the request notification
queue (e.g., Q1) for the targeted worker node is listed in the
session table entry for the session (note that that the identity of
the worker node that is listed in the session table entry could
also be used to identify the correct request notification
queue).
[0064] In the case of a first request for a new session 401, a
load-balancing algorithm 407 (e.g., round robin based, weight based
(e.g., using the number of active (not yet services) request
notifications as weights)) determines which one of the M worker
nodes is to handle the request. The dispatching process then writes
408 a new entry for the session into the session table that
includes: 1) the sticky or distributable characterization for the
session; and, 2) an ARC value of 1 for the session, indicating one
request needs to be responded to; 3) some form of identification of
the worker node that has been targeted; and, 4) the request
notification queue for the worker node identified by 3). In a
further embodiment, the session key described above is also created
for accessing the newly created entry. In one embodiment, the
session key may be created from information found in the header of
the received request.
[0065] The ARC value in the session's session table entry is then
incremented and the request notification RN for the session is
entered into the request notification queue for the worker node
assigned to handle the session at 408. Recall that the request
notification RN includes both a pointer to the request in the
request/response shared memory as well as a pointer (or data
structure that can be used by the targeted worker node) to access
the correct session table entry. The former may be provided by the
functionality of the connection manager that stores the request
into the request/response shared memory and the later may be the
session key.
[0066] If at 402 it is determined the session is a distributable
session, and if at 404 the ARC value obtained from the session's
session table entry is greater than zero, the request is assigned
at 405 to the worker node that has been assigned to handle the
session. Here, an ARC value greater than zero means there still
exists at least one previous request for the session for which a
response has not yet been generated. The ARC value for the session
is then incremented in the session's session table entry and the
request notification RN for the session is directed to the request
notification queue for the worker node assigned to handle the
session.
[0067] If at 404 the ARC value is zero, and if at 406 the request
notification queue for the assigned worker node is empty, the
request is assigned at 405 to the worker node that has been
assigned to handle the session. This action essentially provides an
embedded load balancing technique. Since the request notification
queue is empty for the worker node that has been assigned to handle
the session, the latest request for the session may as well be
given to the same worker node. The ARC value for the session is
then incremented in the session's session table entry and the
request notification RN for the session is directed to the request
notification queue for the worker node assigned to handle the
session at 408.
[0068] Returning to 404, if the ARC value is zero, but the request
notification queue for the previously assigned worker node is
determined at 406 to be not empty (for example, a multi-threaded
worker node could be processing requests for other threads), the
request is assigned to a new worker node 407 (for example, through
a load balancing algorithm). In this case, while there are no
requests waiting for a response for the session (i.e., ARC=0), the
worker node assigned to the session has some backed-up traffic in
its request notification queue, and the session is distributable.
As such, to improve overall efficiency, the request can be assigned
to a new worker node that is less utilized than the previous worker
node assigned to handle the session.
[0069] The above description of the dispatching algorithm assumes a
single session for handling related requests/responses. In an
alternative embodiment, wherein multiplexed sessions are used as
described in section 2.1 above, it is appreciated the dispatcher
receives and processes independent and simultaneous requests
received via separate channels of a session, and therefore
considers a request's channel identifier in addition to it's
session identifier when selecting the appropriate worker node to
process the request in accordance with process 400.
[0070] The ARC value for the session is incremented in the
session's session table entry and the request notification RN for
the session is directed to the request notification queue for the
new worker node that has just been assigned to handle the session
408.
4.0 Session Handling based on Shared Session Information
[0071] As noted above, shared memory is memory whose stored content
can be reached by multiple worker nodes, e.g., connection oriented
request/response shared memory region 250 can be reached by each of
worker nodes in 207 and 209 (including worker nodes 209.sub.1
through 209.sub.M). Additionally, the connection manager is
communicatively coupled to the shared memory region. Thus, the
region provides a transport mechanism for request/response data
between the connection manager and the worker nodes. Moreover, the
shared memory region 270 stores "high level" session state
information that relates to the management and control of the
requests and responses for a session.
[0072] The embodiments described thus far for the most part
contemplate the connection manager creating and managing sessions,
including creating and updating session information in the session
table. However, in one embodiment, a worker node can initiate,
access, or update a session, for example, a logon session or other
session where a client request is not needed to create or update
the session. To do so, the handlers and routines that the
connection manager uses to access and modify the session table,
therefore, are mirrored on the worker nodes side of the session
table shared memory as well.
[0073] In this embodiment, a worker node as well as the connection
manager may create a new session and corresponding entry in the
session table, update the session and corresponding state
information in the session table (e.g., flag the session as
distributable, sticky, or corrupt), initiate freeing a dropped
session, including the session's entry in the session table, and
participate in clean-up of a session table entry, for example, in
the event of termination or failure of a corresponding session (in
which event, the worker node may clean up bindings to the worker
node.
[0074] To this end, a worker node may search for an existing
session by looking up a corresponding session table entry, for
example, using a session ID from a cookie and an alias ID. The
worker node may search the session table, for example, to identify
sessions for which it is responsible for servicing. If no session
exists, the worker node may allocate and initialize an entry in the
session table for the session. Additionally, the worker node may
free an entry in the session table. In one embodiment, the entry is
freed if the ACR=0 (otherwise, it is presumed the connection
manager has sent a new request for the session to the worker node,
and the worker node will re-activate the session). Once a worker
node frees a session, the connection manager may drop the session.
Cleaning up a failed or terminated worker node is described in more
detail below, in section 4.1.
[0075] In one embodiment of the invention, a native language
application programmatic interface (API) may be implemented on the
worker-node side of the shared memory, including the session table
shared memory, to facilitate the operations described above. In one
embodiment wherein the worker nodes are implemented in Java
applications running in a Java virtual machine, the API may use the
Java Native interface (JNI) which allows the worker nodes to access
the API.
4.1 Rescuing Sessions Targeted For a Failed Worker Node
[0076] FIGS. 5 and 6a,b,c together describe a scheme for rescuing
one or more sessions whose request notifications have been queued
into the request notification queue for a particular worker node
that crashes before the request notifications are serviced from the
request notification queue. FIG. 6a shows an initial condition in
which worker nodes 609.sub.1 and 609.sub.2 are both operational. A
first request 627 (whose corresponding request notification is
request notification 624) for a first session is currently being
processed by worker node 609.sub.1. As such, the session object(s)
629 for the first session is also being used by worker node
609.sub.1.
[0077] Request notifications 625, 626 are also queued into the
request notification queue Q1 for worker node 609.sub.1. Request
notification 625 corresponds to a second session that session table
670 entry SK2 and request 628 are associated with. Request
notification 626 corresponds to a third session that session table
entry SK3 and request 629 are associated with.
[0078] FIG. 6b shows activity that transpires after worker node
609.sub.1 crashes at the time of the system state observed in FIG.
6a. Because request notifications 625 and 626 are queued within the
queue Q1 for worker node 609.sub.1 at the time of its crash, the
second and third sessions are "in jeopardy" because they are
currently assigned to a worker node 609.sub.1 that is no longer
functioning. Referring to FIGS. 5 and 6b, after worker node
609.sub.1 crashes, each un-serviced request notification 625, 626
is retracted 501a, 1 from the crashed worker node's request
notification queue Q1; and, each session that is affected by the
worker node crash is identified 501b.
[0079] Here, recall that in an embodiment, some form of
identification of the worker node that is currently assigned to
handle a session's requests is listed in that session's session
table entry. For example, recall that the "Pr_Idx" index value
observed in each session table entry in FIG. 6a is an index in the
process table of the worker node assigned to handle the session's
requests. Assuming the Pr_Idx value has a component that identifies
the applicable worker node outright, or can at least be correlated
to the applicable worker node, the Pr_Idx values can be used to
identify the sessions that are affected by the worker node crash.
Specifically, those entries in the session table having a Pr_Idx
value that corresponds to the crashed worker are flagged or
otherwise identified as being associated with a session that has
been "affected" by the worker node crash.
[0080] In the particular example of FIG. 6b, the SK1 session table
670 entry will be identified by way of a "match" with the Pr_Idx1
value; the SK2 session table 670 entry will be identified by way of
a "match" with the Pr_Idx2 value; and, the SK3 session table 670
entry will be identified by way of a match with the Pr_Idx3
value.
[0081] Referring back to FIG. 5 and FIG. 6b, with the retracted
request notifications 625, 626 at hand and with the affected
sessions being identified, the ARC value is decremented 502, at 2
in the appropriate session table entry for each retracted request
notification. Here, recall that each request notification contains
an identifier of its corresponding session table entry (e.g.,
request notification 625 contains session key SK2 and request
notification 626 contains session key SK3). Because of this
identifier, the proper table entry for decrementing an ARC value
can be readily identified.
[0082] Thus, the ARC value is decremented for the SK2 session entry
in session table 670 and the ARC value is decremented for the SK3
session entry in session table 670. Because the ARC value for each
of the SK1, SK2 and SK3 sessions was set equal to 1.0 prior to the
crash of worker node 609.sub.1 (referring briefly back to FIG. 6a),
the decrement 502, 2 of the ARC value for the SK2 and SK3 sessions
will set the ARC value equal to zero in both of the SK2 and SK3
session table 670 entries as observed in FIG. 6b.
[0083] Because the request notification 624 for the SK1 entry had
been removed from the request notification queue Q1 prior to the
crash, it could not be "retracted" in any way and therefore its
corresponding ARC value could not be decremented. As such, the ARC
value for the SK1 session remains at 1.0 as observed in FIG.
6b.
[0084] Once the decrements have been made for each extracted
request notification 502, at 2, decisions can be made as to which
"affected" sessions are salvageable and which "affected" sessions
are not salvageable. Specifically, those affected sessions that
have decremented down to an ARC value of zero are deemed
salvageable; while, those affected sessions who have not
decremented down to an ARC value of zero are not deemed
salvageable.
[0085] Having the ARC value of an affected session decrement down
to a value of zero by way of process 502 corresponds to the
extraction of a request notification from the failed worker node's
request notification queue for every one of the session's
non-responded to requests. This, in turn, corresponds to
confirmation that the requests themselves are still safe in the
request/response shared memory 650 and can therefore be
subsequently re-routed to another worker node. In the simple
example of FIGS. 6a,b, the second SK2 and third SK3 sessions each
had an ARC value of 1.0 at the time of the worker node crash, and,
each had a pending request notification in queue Q1. As such, the
ARC value for the second SK2 and third SK3 sessions each
decremented to a value of zero which confirms the existence of
requests 628 and 629 in request/response shared memory 650.
Therefore the second SK2 and third SK3 sessions can easily be
salvaged simply by re-entering request notifications 625 and 626
into the request notification queue for an operational worker
node.
[0086] The first session SK1 did not decrement down to a value of
zero, which, in turn, corresponds to the presence of its request
RQD_1 624 being processed by the worker node 609.sub.1 at the time
of its crash. As such, the SK1 session will be marked as
"corrupted" and eventually dropped.
[0087] As another example, assume that each of the request
notifications 624, 625, 626 are for the same "first" SK1 session.
In this case there would be only one session table 670 entry SK1 in
FIG. 6a (i.e., entries SK2 and SK3 would not exist) and the ARC
value in entry SK1 would be equal to 3.0 because no responses for
any of requests 627, 628 and 629 have yet been generated. The crash
of worker node 609, and the retraction of all of the request
notifications 628, 629 from request notification queue Q1 would
result in a final decremented down value of 1.0 for the session.
The final ARC value of 1.0 would effectively correspond to the
"lost" request 627 that was "in process" by worker node 609.sub.1
at the time of its crash.
[0088] Referring to FIGS. 5 and 6b, once the salvageable sessions
are known, the retracted request notifications for a same session
are assigned to a new worker node based on a load balancing
algorithm 503. The retracted request notifications are then
submitted to the request notification queue for the new worker node
that is assigned to handle the session; and, the corresponding ARC
value is incremented in the appropriate session table entry for
each re-submitted request notification.
[0089] Referring to FIG. 6c, worker node 609.sub.2 is assigned to
both the second and third sessions based on the load balancing
algorithm. Hence request notifications 625, 626 are drawn being
entered at 3 into the request notification queue Q2 for worker node
609.sub.2. The ARC value for both sessions is incremented to a
value of 1.0. In the case of multiple retracted request
notifications for a same session, in an embodiment, all
notifications of the session would be assigned to the same new
worker node and submitted to the new worker node's request
notification queue in order to ensure FIFO ordering of the request
processing. The ARC value would be incremented once for each
request notification.
[0090] From the state of the system observed in FIG. 6c, each of
request notifications 625, 626 would trigger a set of processes as
described in FIGS. 3a,b with worker node 609.sub.2. Importantly,
upon receipt of the request notifications 625, 626 the new targeted
worker node 609.sub.2 can easily access both the corresponding
request data 628, 629 (through the pointer content of the request
notifications and the shared memory architecture) and the session
object(s) 622, 623 (through the request header content and the
shared memory architecture).
[0091] Note that if different worker nodes were identified as the
new target nodes for the second and third sessions, the request
notifications 625, 626 would be entered in different request
notification queues.
[0092] For distributable sessions, reassignment to a new worker
node is a non issue because requests for a distributable session
can naturally be assigned to different worker nodes. In order to
advocate the implementation of a distributable session, in an
implementation, only the session object(s) for a distributable
session is kept in shared closure shared memory 660. Thus, the
examples provided above with respect to FIGS. 3a,b and 6a,b,c in
which low level session object(s) are stored in shared closure
shared memory would apply only to distributable sessions. More
details concerning shared closure shared memory are provided in
section 6.0 "Implementation Embodiment of Shared Closure Shared
Memory".
[0093] For sticky sessions various approaches exist. According to a
first approach, session fail over to a new worker node is not
supported and sticky sessions are simply marked as corrupted if the
assigned worker node fails (recalling that session table entries
may also include a flag that identifies session type).
[0094] According to a second approach, session fail over to a new
worker node is supported for sticky sessions. According to an
extended flavor of this second approach, some sticky sessions may
be salvageable while others may not be. According to one such
implementation, the session object(s) for a sticky session are kept
in the local memory of a virtual machine of the worker node that
has been assigned to handle the sticky session (whether the sticky
session is rescuable or is not rescuable). Here, upon a crash of a
worker node's virtual machine, the session object(s) for the sticky
session that are located in the virtual machine's local memory will
be lost.
[0095] As such, a sticky sessions can be made "rescuable" by
configuring it to have its session object(s) serialized and stored
to "backend" storage (e.g., to a hard disk file system in the
application server or a persisted database) after each request
response is generated. Upon a crash of a worker node assigned to
handle a "rescuable" sticky session, after the new worker node to
handle the sticky session is identified (e.g., through a process
such as those explained by FIGS. 5a and 5b), the session object(s)
for the sticky session are retrieved from backend storage,
deserialized and stored into the local memory of the new worker
node's virtual machine. Here, sticky sessions that are not
configured to have their session object(s) serialized and stored to
backend storage after each response is generated are simply lost
and will be deemed corrupted.
5.0 Implementation Embodiment of Request/Response Shared Memory
[0096] Recall from above that according to a particular
implementation, the request/response shared memory 250 has a
connection oriented architecture. Here, a connection is established
between the targeted worker node and the connection manager across
the request/response shared memory 350 for each request/response
cycle between the connection manager and a worker node. Moreover, a
handle to a particular connection is used to retrieve a particular
request from the request/response shared memory.
[0097] The connection oriented architecture allows for easy session
handling transfer from a crashed worker node to a new worker node
because the routing of requests to a new targeted worker node is
accomplished merely by routing the handle for a specific
request/response shared memory connection to the new worker node.
That is, by routing the handle for a request/response shared memory
connection to a new worker node, the new worker node can just as
easily "connect" with the connection manager to obtain a request as
the originally targeted (but now failed) worker node. Here, the
"pointer" contained by the request notification is the handle for
the request's connection. By moving the request notification to
another worker node's request notification queue, the handle for
the request/response shared memory is passed to the new worker
node.
[0098] FIG. 7 shows an embodiment of an architecture for
implementing a connection based queuing architecture. According to
the depiction in FIG. 7, the connection based queuing architecture
is implemented at the Fast Channel Architecture (FCA) level 702.
The FCA level 702 is built upon a Memory Pipes technology 701 which
is a legacy "semaphore based" request/response shared memory
technology 106 referred to in the Background. The FCA level 702
includes an API for establishing connections with the connection
manager and transporting requests through them.
[0099] In a further embodiment, referring to FIGS. 2 and 7, the FCA
level 702 is also used to implement each of the request
notification queues 212. As such, the request notification queues
212 are also implemented as a shared memory technology. Notably,
the handlers for the request notification queues 212 provide more
permanent associations with their associated worker nodes. That is,
as described, each of the request notification queues 212 is
specifically associated with a particular worker node and is
"on-going". By contrast, each request/response connection
established across request/response shared memory 250 is made
easily useable for any worker node (to support fail over to a new
worker node), and, according to an implementation, exist only for
each request/response cycle.
[0100] Above the FCA level 702 is the jFCA level 703. The jFCA
level 703 is essentially an API used by the Java worker nodes and
relevant Java parts of the connection manager to access the FCA
level 702. In an embodiment, the jFCA level is modeled after
standard Java Networks Socket technology. At the worker node side,
however, a "jFCA connection" is created for each separate
request/response cycle through request/response shared memory; and,
a "jFCA queue" is created for each request notification queue.
Thus, whereas a standard Java socket will attach to a specific
"port" (e.g., a specific TCP/IP address), according to an
implementation, the jFCA API will establish a "jFCA queue" that is
configured to implement the request notification queue of the
applicable worker node and a "jFCA connection" for each
request/response cycle.
[0101] Here, an instance of the jFCA API includes the instance of
one or more objects to: 1) establish a "jFCA queue" to handle the
receipt of request notifications from the worker node's request
notification queue; 2) for each request notification, establishing
a "jFCA connection" over request/response shared memory with the
connection manager so that the corresponding request from the
request/response shared memory can be received (through the jFCA's
"InputStream"); and, 3) for each received request, the writing of a
response back to the same request/response shared memory connection
established for the request (through the jFCA's
"OutputStream").
[0102] In the outbound direction (i.e., from the worker node to the
connection manager), in an embodiment, the same jFCA connection
that is established through the request/response shared memory
between the worker node and the connection manager for retrieving
the request data is used to transport the response back to the
connection manager.
[0103] In a further embodiment, a service (e.g., an HTTP service)
is executed at each worker node that is responsible for managing
the flow of requests/responses and the application(s) invoked by
the requests sent to the worker node. In a further embodiment, in
order to improve session handling capability, the service is
provided its own "dedicated thread pool" that is separate from the
thread pool that is shared by the worker node's other applications.
By so doing, a fixed percentage of the worker node's processing
resources are allocated to the service regardless of the service's
actual work load. This permits the service to immediately respond
to incoming requests during moments of light actual service work
load and guarantees a specific amount of performance under heavy
actual service workload.
[0104] According to one implementation, each thread in the
dedicated thread pool is capable of handling any request for any
session. An "available" thread from the dedicated thread pool
listens for a request notifications arriving over the jFCA queue.
The thread services the request from the jFCA queue and establishes
the corresponding jFCA connection with the handler associated with
the request notification and reads the request from
request/response shared memory. The thread then further handles the
request by interacting with the session information associated with
the request's corresponding session.
[0105] Each worker node may have its own associated container(s) in
which the service runs. A container is used to confine/define the
operating environment for the application thread(s) that are
executed within the container. In the context of J2EE, containers
also provide a family of services that applications executed within
the container may use (e.g., (e.g., Java Naming and Directory
Interface (JNDI), Java Database Connectivity (JDBC), Java Messaging
Service (JMS) among others).
[0106] Different types of containers may exist. For example, a
first type of container may contain instances of pages and servlets
for executing a web based "presentation" for one or more
applications. A second type of container may contain granules of
functionality (generically referred to as "components" and, in the
context of Java, referred to as "beans") that reference one another
in sequence so that, when executed according to the sequence, a
more comprehensive overall "business logic" application is realized
(e.g., stringing revenue calculation, expense calculation and tax
calculation components together to implement a profit calculation
application).
6.0 Embodiment of Shared Closure Based Shared Memory
[0107] Recall from the discussion in the Background pertaining to
FIG. 1b that a virtual machine crash is not an uncommon event, and
that, in the prior art worker nodes 109 of FIG. 1b, a large number
of sessions could be "dropped" by a single virtual machine crash
because a large number of sessions were concurrently being executed
by a single virtual machine.
[0108] FIG. 8 shows worker nodes 809 configured with less
application threads per virtual machine than the prior art system
of FIG. 1b. Less application threads per virtual machine results in
less application thread crashes per virtual machine crash; which,
in turn, should result in the application server exhibiting better
reliability than the worker nodes 109 of FIG. 1b.
[0109] According to the depiction of FIG. 8, which is an ideal
representation of the improved approach, only one application
thread exists per virtual machine (specifically, thread 122 is
being executed by virtual machine 123; thread 222 is being executed
by virtual machine 223; . . . , and, thread M22 is being executed
by virtual machine M23). In practice, within worker nodes 809 of
FIG. 8, a limited number of threads may be concurrently processed
by a virtual machine at a given time rather than only one. However,
for simplicity, the present discussion will refer to the model
depicted in FIG. 8 in which only one thread is concurrently
processed per virtual machine.
[0110] In order to concurrently execute as many (or approximately
as many) application threads as the worker nodes 109 of FIG. 1b,
the improved approach of FIG. 8 instantiates comparatively more
virtual machines than the prior art system 109 of FIG. 1b. That is,
M>N. Thus, for example, if the worker nodes 109 of FIG. 1b has
20 threads per virtual machine and 8 virtual machines (for a total
of 160 concurrently executed threads by the worker nodes 109 as a
whole), the worker nodes 809 of FIG. 8 will have 1 thread per
virtual machine and 160 virtual machines (to implement the same
number of concurrently executed threads as the worker nodes 109 in
FIG. 1b).
[0111] Recall from the discussion of FIG. 1b that a virtual machine
can be associated with its own local memory. Because the improved
approach of FIG. 8 instantiates comparatively more virtual machines
that the prior art approach of FIG. 1b, in order to conserve memory
resources, the virtual machines 813, 823, . . . M23 of the worker
nodes 809 of FIG. 8 are configured with comparatively less local
memory space 125, 225, . . . M25 than the virtual machines 113,
123, . . . N23 of FIG. 1b.
[0112] Moreover, the virtual machines 213, 223, . . . M23 of worker
nodes 809 of FIG. 8 are configured to use a shared closure shared
memory 860 (which corresponds to shared memory region 260, 360 and
660 in FIGS. 2, 3a,b and 6a,b,c). Shared closure shared memory 860
is memory space that contains items that can be accessed by more
than one virtual machine (and, typically, any virtual machine
configured to execute "like" application threads).
[0113] Thus, whereas the worker nodes 109 of FIG. 1b use
comparatively fewer virtual machines with larger local memory
resources containing objects that are "private" to the virtual
machine; the worker nodes 809 of FIG. 8, by contrast, use more
virtual machines with comparatively less local memory resources.
The less local memory resources allocated per virtual machine is
compensated for by allowing each virtual machine to access
additional memory resources. However, owing to limits in the amount
of available memory space, this additional memory space 860 is made
"shareable" amongst the virtual machines 123, 223, . . . M23.
[0114] According to an object oriented approach where each of
virtual machines 123, 223, . . . N23 does not have visibility into
the local memories of the other virtual machines, specific rules
are applied that mandate whether or not information is permitted to
be stored in shared closure shared memory 860. Specifically, to
first order, according to an embodiment, an object residing in
shared closure shared memory 860 should not contain a reference to
an object located in a virtual machine's local memory because an
object with a reference to an unreachable object is generally
deemed "non useable".
[0115] That is, if an object in shared closure shared memory 860
were to have a reference into the local memory of a particular
virtual machine, the object is essentially non useable to all other
virtual machines; and, if shared closure shared memory 860 were to
contain an object that was useable to only a single virtual
machine, the purpose of the shared memory 860 would essentially be
defeated.
[0116] In order to uphold the above rule, and in light of the fact
that objects frequently contain references to other objects (e.g.,
to effect a large process by stringing together the processes of
individual objects; and/or, to effect relational data structures),
"shareable closures" are employed. A closure is a group of one or
more objects where every reference stemming from an object in the
group which references another object does not reference an object
outside the group. That is, all the object-to-object references of
the group can be viewed as closing upon and/or staying within the
confines of the group itself. Note that a single object without any
references stemming from it meets the definition of a closure.
[0117] Thus, in order to prevent a reference from an object in
shared closure shared memory 860 to an object in a local memory,
only "shareable" (or "shared") closures may be stored in shared
memory 860. In order to render a closure as "shareable", each
object in the closure must be "shareable". A shareable object is an
object that can be used by other virtual machines that store and
retrieve objects from the shared closure shared memory 860. If a
closure with a non shareable object were to be stored in shared
closure shared memory 860, the closure itself would not be
shareable with other virtual machines, which, again, defeats the
purpose of the shared memory 860.
[0118] As discussed above, in an embodiment, one aspect of a
shareable object is that it does not possess a reference to another
object that is located in a virtual machine's local memory. Other
conditions that an object must meet in order to be deemed shareable
may also be affected. For example, according to a further
embodiment, a shareable object must also posses the following
characteristics: 1) it is an instance of a class that is
serializable; 2) it is an instance of a class that does not execute
any custom serializing or deserializing code; 3) it is an instance
of a class whose base classes are all serializable; 4) it is an
instance of a class whose member fields are all serializable; and,
5) it is an instance of a class that does not interfere with proper
operation of a garbage collection algorithm.
[0119] Exceptions to the above criteria are possible if a copy
operation used to copy a closure into shared memory 860 (or from
shared memory 860 into a local memory) can be shown to be
semantically equivalent to serialization and deserialization of the
objects in the closure. Examples include instances of the Java 2
Platform, Standard Edition 1.3 java.lang.String class and
java.util.Hashtable class.
7.0 Additional Comments
[0120] The architectures and methodologies discussed above may be
implemented with various types of computing systems such as an
application server that includes a Java 2 Enterprise Edition
("J2EE") server that supports Enterprise Java Bean ("EJB")
components and EJB containers (at the business layer) and/or
Servlets and Java Server Pages ("JSP") (at the presentation layer).
Of course, other embodiments may be implemented in the context of
various different software platforms including, by way of example,
Microsoft .NET, Windows/NT, Microsoft Transaction Server (MTS), the
Advanced Business Application Programming ("ABAP") platforms
developed by SAP AG and comparable platforms.
[0121] Processes taught by the discussion above may be performed
with program code such as machine-executable instructions which
cause a machine (such as a "virtual machine", a general-purpose
processor disposed on a semiconductor chip or special-purpose
processor disposed on a semiconductor chip) to perform certain
functions. Alternatively, these functions may be performed by
specific hardware components that contain hardwired logic for
performing the functions, or by any combination of programmed
computer components and custom hardware components.
[0122] An article of manufacture may be used to store program code.
An article of manufacture that stores program code may be embodied
as, but is not limited to, one or more memories (e.g., one or more
flash memories, random access memories (static, dynamic or other)),
optical disks, CD-ROMs, DVD ROMs, EPROMs, EEPROMs, magnetic or
optical cards or other type of machine-readable media suitable for
storing electronic instructions. Program code may also be
downloaded from a remote computer (e.g., a server) to a requesting
computer (e.g., a client) by way of data signals embodied in a
propagation medium (e.g., via a communication link (e.g., a network
connection)).
[0123] FIG. 9 is a block diagram of a computing system 900 that can
execute program code stored by an article of manufacture. It is
important to recognize that the computing system block diagram of
FIG. 9 is just one of various computing system architectures. The
applicable article of manufacture may include one or more fixed
components (such as a hard disk drive 902 or memory 905) and/or
various movable components such as a CD ROM 903, a compact disc, a
magnetic tape, etc. In order to execute the program code, typically
instructions of the program code are loaded into the Random Access
Memory (RAM) 905; and, the processing core 906 then executes the
instructions. The processing core may include one or more
processors and a memory controller function. A virtual machine or
"interpreter" (e.g., a Java Virtual Machine) may run on top of the
processing core (architecturally speaking) in order to convert
abstract code (e.g., Java bytecode) into instructions that are
understandable to the specific processor(s) of the processing core
906.
[0124] It is believed that processes taught by the discussion above
can be practiced within various software environments such as, for
example, object-oriented and non-object-oriented programming
environments, Java based environments (such as a Java 2 Enterprise
Edition (J2EE) environment or environments defined by other
releases of the Java standard), or other environments (e.g., a NET
environment, a Windows/NT environment each provided by Microsoft
Corporation).
[0125] In the foregoing specification, the invention has been
described with reference to specific exemplary embodiments thereof.
It will, however, be evident that various modifications and changes
may be made thereto without departing from the broader spirit and
scope of the invention as set forth in the appended claims. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense.
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