ORACLE SERVER AND UNIX TP MONITOR-2

Question

제품 : ORACLE SERVER
작성날짜 : 1995-01-24
Subject: Oracle Server and UNIX Transaction Processing Monitors-2
Page(3/4)
This file contains commonly asked questions about Oracle7 Server and UNIX
Transaction Processing Monitors (TPMs). The topics covered in this article are
     o Oracle Parallel Server and TP Monitors
     o Oracle and DCE-based TP Monitors
     o Other commonly asked questions
The questions answered in part 3 provide additional detail to the information
provided in part 1.
Oracle Parallel Server and TP Monitors
======================================
How does Oracle Parallel Server (OPS) work with TP Monitors?
If you are using Oracle-managed transactions, there are no special
considerations. But if you are using TPM-managed transactions, and
thus need to use the XA interface, then Oracle requires release 7.1.3
or later and a special version of the Distributed Lock Manager, called
the session-based lock manager. This version of the DLM is not yet
available for all platforms. To understand this restriction, let's take
a look at one of the technical details of XA.
The XA specification requires that the Resource Manager be able to
move a transaction from one process to another, and even to be
able to commit in a separate process. In Oracle, transactions are
attached to sessions, so that means that we also have to be able to
move sessions. Therefore, the session/transaction can't have any state
which is tied to a particular process. The first generation distributed
lock managers were all built to use the process id as the lock owner,
which doesn't work for locks which need to move with the transaction.
Oracle and DCE-based TP Monitors
================================
How does Oracle interface to the Encina TP monitor? To CICS/6000? I've
heard that they require OSF DCE facilities in order to run?
Oracle interfaces to Encina and CICS/6000 just as it does to any other
TP Monitor. The TP Monitor issues XA commands to control transactions, and
Oracle executes the commands. Encina and CICS/6000 do use DCE features for
their own operation. However, this use is transparent to the Oracle Server.
What DCE facilities can Oracle products take advantage of when working with
a DCE-based TP Monitor?
The two most commonly mentioned DCE features which might be useful
to Oracle users are multi-threading and security. We look at these in
the subsequent questions in this section.
Encina documentation suggests that a Resource Manager such as Oracle can
be either single-threaded or multi-threaded? Which way is Oracle XA
implemented?
The Oracle XA implementation is single-threaded, as is any Oracle client.
Within a single process, at most one thread can access Oracle at a time.
Does that mean that only a single Encina application can access an instance
of Oracle transactionally at any given moment?
No. Oracle XA is only single-threaded within a single application server
process. Multiple applications can access Oracle simultaneously using XA
by using different application processes. Encina allows
(1) serial reuse of a single server by different clients. There are
two options for this. The server can use long term reservation
but be defined to be in shared or concurrent access mode, which
allows the server to be used by another client as soon as an RPC
completes. Alternatively, the server can use default reservation
and exclusive mode, which allows the server to be used by another
client as soon as the current transaction ends.
(2) concurrent execution by multiple servers, even if they are accessing
the same Oracle database. These may be executing the same or different
procedures.
These two features should let you get as much concurrency as you need.
Why isn't the Oracle XA library multi-threaded?
The XA specification specifically states that its use of the phrase
"thread of control" means a process. If an RM were to multi-thread its
XA, it would be in violation of the specification. This restriction
was put place in because at the time the specification was written,
there were numerous thread packages: if the TM used one, the application
another, and perhaps the RM yet a third, there's no way it could work.
As threads standards settle down, the later versions of XA will probably
relax this restriction.
Will Oracle change if the XA specification changes?
Very likely. The exact time frame will of course depend on the priority of
all work items at that time.
Does Oracle use DCE security via the TP Monitors?
The integrity of the connection between a DCE TP Monitor client and DCE
TP Monitor server is protected by the DCE security functionality.
Theoretically, the TP Monitor could make the DCE-protected client security
information available to Oracle. Unfortunately, there's no standard way
for a TP Monitor to pass security information information to a Resource
Manager such as Oracle. Oracle is leading an effort to extend the X/Open
model to allow use of the security information provided by the Monitor.
In the meantime, the basic DCE security features such as encryption are
useful within TP Monitors.
Effective use of DCE security would normally also mean that the security of
the TP Monitor client be passed through the TP Monitor, through the Oracle
client (application server), to the Oracle Server, and possibly on
to other Oracle Servers through database links. The ability to transfer
security information to other processes, called delegation, is missing
in DCE version 1.0. DCE version 1.1, expected to emerge in late 1994,
has some delegation features. Oracle is examining these features to see
how they might be used.
Are there any special considerations for CICS/6000?
There are two:
(1) It is inefficient to run without XA. CICS/6000 is designed to
use XA. It uses XA so that the CICS server can log on to Oracle
when it starts, after which it makes that Oracle connection available
to any transaction it executes. If you don't use XA, the CICS server
does not itself log on to Oracle so each transaction has to log on
and log off - a very expensive mode of operation. Also, it is very
un-cics-like in that the application does the log{on,off} and also
commits - in a mainframe CICS database program CICS would implicitly
do these operations. Oracle does not recommend this mode because of the
performance penalty.
(2) CICS servers are generic and dynamically load application modules.
In order for these modules to access the Oracle connection made by
CICS, the applications must be built with a shared object version of
the Oracle libraries. This is an installation option on platforms which
support CICS/6000 and other products using its architecture such as
CICS 9000.
Other commonly asked questions
==============================
What other Resource Managers can be included in an Oracle XA transaction?
Several other relational database vendors have an XA implementation
available or in progress. There is an XA C-ISAM product from
Gresham Telecomputing. There are also Resource Managers contained
within some of the TP Monitors which can be coordinated in the same
transaction. For example, CICS/6000 has VSAM files and other data
stores, Encina has its RQS queuing system, and Tuxedo has its /Q queuing
system.
What is Recoverable Queuing Service (RQS) and how does it interoperate with
Oracle7 and Encina? What about /Q?
Recoverable Queuing Service is a feature provided by Encina which allows
transactional, distributed queuing (enqueue/dequeue). Tuxedo has a similar
product called /Q. Because these products are themselves coordinated by the
TM component of the TP Monitor, their queue operations are atomically
coordinated with with operations on XA Resource Managers such as Oracle7
Server. That is, they can atomically put something on one of their queues
and commit an Oracle transaction, then at some later time dequeue an
entry atomically with doing some other Oracle transaction. The queue
system guarantees that the message will not be lost or transmitted twice.
Can I mix TP Monitor applications with standard Oracle7 Server applications?
Yes, you can have existing Oracle applications connected to the database
with alongside TPM applications against the same database. The TPM does
not manage the whole database, just those transactions which are started
by the TPM. The Oracle Server will properly handle concurrency control
between the transactions managed by itself and those managed by the TPM.
Is Oracle planning to change its tools to be more suitable for TP Monitors?
With Oracle Procedure Builder 1.5, to be available with CDE2,
Oracle will provide a foreign function interface that allows you to
dynamically set up PL/SQL calls that access C functions. In other
words, you can access C routines in Windows DLLs from within your
PL/SQL procedures. This will allow PL/SQL under Windows easy access to
TP Monitor APIs.
Does Oracle7 Server itself use XA-compliant TPMs as the interface to
foreign RMs?
No, for this purpose Oracle Server uses the SQL*Connect products or the new
Transparent and Procedural Gateway products.
Does Oracle7 Server use XA to coordinate Oracle7-only distributed
transactions?
No, it uses an internal mechanism.
Can database links be used with XA?
If an Oracle7 database is running under XA, it can access other Oracle7
databases through database links, with some restrictions. First, the
access to the other database must use SQL*Net V2 and be running MTS.
Second, it must currently be to another Oracle7 database. Assuming those
restrictions, the Oracle 7 database can do distributed update to another
Oracle 7 database by using a database link, whether it is started by an
Oracle application or a TP Monitor application. The TPM will see Oracle
as only a single RM, but Oracle7 will propagate all the transaction
commands to the other database, including the two-phase commit. If
the transaction is started by a TP Monitor application and is using XA,
it can also update non-Oracle resources managed by the TPM. If it
is started from an Oracle application, it can only include resources
managed by Oracle.
Here's a sample configuration:
| TPM | | TPM |
| client | | client |
| |
| |
| TPM |
| |
| |
| Oracle | Forms, Forms, | Oracle | | non-XA | | XA |
| client | Plus, Plus, | client | | TPM | | TPM |
--------- Pro, Pro, --------- | server | | server |
| Financials, Financials, | |(note 1)| ----------
| etc. etc. | ---------- |
| | | |
| SQL | SQL | SQL | XA
| commit | commit | commit | commit
| | | |
| Oracle | | Oracle | | Oracle | | Oracle |
| server | | server | | server | | server |
| | | |
| | | |
| | | |
| Database 1 | | Database 2 |
| | | |
| A | A
| | dblink to database 1 | |
| ------------------------------------ |
| |
dblink to database 2
Note 1: Oracle will work having both XA and non-XA servers but some TPMs
may have restrictions on this.
Are multiple direct connections possible from a Pro* program?
Using XA, you can not only specify multiple direct connections to Oracle7
databases, you can also update them both in the SAME transaction. The
way to do this is to use a precompiler feature called a named database.
When you use a named database, you qualify the SQL statement with the
database name. For example, you write EXEC SQL AT dbname UPDATE emp ....
We have a complementary feature in the xa open string to let the user
associate the name with a particular RM instance, called the DB clause.
You will also want to use the SqlNet clause in the open string so you
can give the two different SIDs. This clause does not require the use of
the SQL*Net product, it is just a naming convention. For more information,
see Oracle7 Server for UNIX Administrator's Reference Guide.
Some TP Monitors may not support having multiple Resource Mangers in the
same server; check with the TPM vendor.
Is there any collateral available for XA or TP Monitors?
Oracle At Work 52684.0692
Oracle7 Server for UNIX Administrator's #A10324-1
Reference Guide
Guide to Oracle's Products and Services #A10560
Oracle7 Server and CICS/6000               #A14200
Where can I get more information on the DTP model?
X/Open's address is
X/Open company Ltd (Publications)
P O Box 109
Penn
High Wycombe
Bucks HP10 8NP
Tel: [phone]
Fax: [phone]
Request
G307 Distributed Transaction Processing: Reference Model Version 2
X/Open Guide G307 ISBN 1-859120-19-9 28cm.44p.pbk.220g.11/93
Page(4/4)
This file contains commonly asked questions about Oracle Server and UNIX
Transaction Processing Monitors (TPMs). The topics covered in this article are
     o Performance with Oracle Server and TP monitors
     o Performance using Oracle's XA Library
The questions answered in part 4 provide additional detail to the information
provided in part 1.
Performance with Oracle Server and TP Monitors
==============================================
I have heard that Transaction Processing Monitors (TPMs) will increase
Oracle Server performance. Is this true?
Several hardware and TPM vendors have made the claim that TPMs
will increase RDBMS performance. This claim is based on TPC-A
benchmarks. The key point to understand about TPC-A is that it
requires, for every transaction-per-second, ten times that many
users to be connected. For example, to get 600 TPS, you need 6000
users. The next question will answer in more detail how the the
three-tier architecture addresses this requirement, but first let's
look more generally at what TP Monitors can and can't do to improve
performance.
TP Monitors can provide better performance:
(1) When there are more than several hundred users connected.
     This is because of the TP Monitor's role in the three-tier
     architecture, described in the next question. In this
     architecture, terminal handling is offloaded to one or more
     separate machines, freeing up those cycles to do database work.
     Note that this does NOT mean that Oracle itself runs faster,
     just that we've given it more CPU cycles to use.
(2) When, because of the high potential concurrency of requests,
     significant resource contention exists. Use of a TP Monitor can
     limit the degree of concurrency and thus reduce contention.
TP Monitors can not provide better performance:
(1) For existing applications. The applications must be designed
     to fit the TP Monitor architecture.
(2) For applications which are highly interactive in their use of
     the database. These applications put many messages
     through the transport system, and the TP Monitor is not as
     efficient as SQL*Net for point-to-point communication.
(3) For CPU intensive single-query decision support. When executing
     a single large command, Oracle query facilities work efficiently,
     especially with the use of Oracle Parallel Query, available in 7.1.
How does the three-tier solution help TPC-A, or other situations with
thousands of on-line users?
The TPC-A test calls for a large number of users to produce a given
result. In the high-end results we produced in June, 1992, for example,
6150 terminals were simulated to produce 618 TPC-A transactions.
Thus, terminal concentration accounts for a large portion of the total
processing time used.
First, let's look at how the Multi Threaded Server would work for
this benchmark. In this case, there are many client processes,
but only a few server processes, which handle client requests on a
first-come first serve basis. When they are done with a request,
they take another client's request.
ORACLE7 CLIENT/SERVER ARCHITECTURE WITH MULTI THREADED SERVER
| Client | | Server |
| __________ |______________|_____ _____________ _____________ |
| | Client | | SQL*Net | |_|Dispatcher | | | |
| | Process| | | ____| Process |___| | |
| |________| | | | __|___________| | | |
|____________| | | | | | | | |
| | | | | | Oracle7 | |
______________ | | | __|__|____ | Server | |
| Client | | | | __|_|_____ | | | |
| __________ | | | | | Shared | |____| | |
| | Client | | SQL*Net | | | | Server |_|____| | |
| | Process|_|______________|__| | | Process|_| | | |
| |________| | | | |________| |___________| |
|____________| | | |
| | |
______________ | | |
| Client | | | |
| __________ | | | |
| | Client | | SQL*Net | | |
| | Process|_|______________|____| |
| |________| | | |
|____________| | |
|_______________________________________|
Client processes = N Dispatcher processes >= 1
Shared server processes >= 1
If there are 500 clients in this environment, there will be one or more
dispatcher processes, dynamically tunable, and one or more shared
server processes, dynamically tunable, on the server. The reduction
in the total number of processes handled by the server system
results in more processing time available for RDBMS activity. Thus
higher RDBMS transaction throughput can be obtained on the
server system.
But the problem for the TPC-A, and for certain large customer
configurations, is not the only ability of the Oracle Server to
process transactions, but also the ability of the operating
system to handle huge numbers of incoming connections.
There is one incoming connection for each client. Most UNIX
operating systems have a limit on how many such connections they can
handle. Even if a particular operating system allows a large number of
connections, each takes some amount of overhead to manage.
In order to service all 6150 terminals, we selected a 3-tier hardware
environment where the middle tier, using a TPM, acted as a terminal
concentrator. The high-end TPC-A architecture looked like the following.
The Application Servers, which contain the Pro*C statements used to
perform the transaction also run on the terminal concentrator machine
in order to offload as much work from the database serve as possible.
They send the compiled SQL over SQL*Net to the Oracle7 Server processes.
ORACLE7 TPS-A CLIENT/SERVER ARCHITECTURE
| Client | | Terminal | | Server |
| ________ | | Concentrator | | |
| | Client | |TPM | | | |
| | Process|_|_____|__ _____ | | |
| |________| |Comm | | | | | | |
|____________| | | | | | | |
| |__| | | | |
____________ | | TPM | | | |
| Client | | ___| | _______ | | ________ _______ |
| ________ | | | | |_| |__|_______|__| Oracle | | | |
| | Client | |TPM | | | | |Appl. | |SQL*Net| | Server |__| | |
| | Process|_|_____|_| |_____| |Server | | | | Process| | | |
| |________| |Comm | |_______| | | |________| | | |
|____________| | | | | | |
|_______________________| | | | |
| | | |
____________ _______________________ | |Oracle7| |
| Client | | Terminal | | |Server | |
| ________ | | Concentrator | | | | |
| | Client | |TPM | | | | | |
| | Process|_|_____|__ _____ | | __________ | | |
| |________| |Comm | | | | _______ |SQL*Net| | Oracle | | | |
|____________| | | | |_| |__|_______|__| Server |__| | |
| |__| | |Appl. | | | | Process| | | |
____________ | | TPM | |Server | | | |________| |_______| |
| Client | | ___| | |_______| | | |
| ________ | | | | | | | |
| | Client | |TPM | | | | | | |
| | Process|_|_____|_| |_____| | | |
| |________| |Comm | | | |
|____________| | | | |
|_______________________| |________________________|
Clients = 6150 Terminal concentrators = 17
TP Monitor instances = 17
Application server processes Oracle Server processes
= 17*8 = 17*8
The TPM is the software component of the terminal concentrator. In this role
it offloads terminal handling from the the machine running Oracle Server.
Since more than one terminal concentrator can be configured, whereas the
database in this case had to run on a single machine, concentrator machines
can be added until the performance of the back-end machine was optimized.
This three-tier solution resulted in the outstanding transaction throughput
announced with Oracle7 Server. Even with Oracle Parallel Server, it may pay
to offload the terminal handling so that the cluster can be exclusively used
for database operations.
Can you summarize the performance discussion for me?
Depending on the number of users required, different architectures may be
used in a client/server environment to maximize performance:
1) For a small number of users, the traditional Oracle two-task
architecture can be used. In this case, there is a one-to-one
correspondence between client processes and server processes. It's
simple, straightforward, and efficient.
2) For a large number of users, Multi Threaded Server might be a better
approach. Although some tuning may be required, Multi Threaded Server
can handle a relatively large number of users for each machine size
compared to the traditional Oracle approach. Using this approach,
customers will be able to handle many hundreds of users on many
platforms. Furthermore, current Oracle applications can move to this
environment without change.
3) For a very large number of users, where transactions are simple and
terminal input concentration is the overriding performance issue, a
3-tier architecture incorporating a TPM may be useful. In this case,
terminal concentration is handled by the TPM in the middle tier. As
     you might expect, it is a more complex environment requiring more
     system management. For existing Oracle customers, significant Oracle
application modifications will be required.
Oracle provides all of these choices.
Performance using Oracle's XA Library
=====================================
Are there any performance implications to using the XA library (in other
words, to using TPM-managed transactions)?
(1) The XA library imposes some performance penalty. You should use
TPM-managed transactions only if you actually need them. Even if you
are getting the one-phase commit optimization, the code path is
longer because we need to map back and forth between external
formats and internal ones. Also, prior to 7.1, XA requires you
to release all cursors at the end of a transaction, which results
in extra parsing. Even with shared cursors, there is time spent
looking up the one you need and re-validating it. This has been
improved for 7.1.
(2) If you need to use two-phase commit, this will incur additional cost
since extra I/Os are required. If you do need 2PC, you need to account
for that when sizing the application.
(3) Although some TPMs allow parallel execution of services (such as Tuxedo's
"tpacall"), this will not normally enhance performance unless different
resource managers are being used. In fact, Oracle Server must serialize
accesses to the same transaction by the same Oracle instance, and the
block/resume code will in fact degrade performance in that case compared
to running the services sequentially.

Answer 1

hello,
the role is the same on all plattforms. the reports server takes requests for running reports, spawns an engine that executes the request. in addition to that, the server also provides scheduling services and security features for the reports environment.
regards,
the oracle reports team