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Friday, November 16, 2012

Using Two Temporary Tablespaces in PeopleSoft

A longer version of this posting, with all necessary code and a demonstration test, is available as a technical note on the Go-Faster website.  I am working with two different PeopleSoft customers who have had challenges with the size of the temporary tablespaces.  Critical batch processes have failed because they have exhausted space in the temporary tablespace.
ORA-01652 unable to extend temporary segment...
  • In one case, the one and only temporary tablespace in a Payroll system has over time been extended to in excess of 360 GB.  This has happen in response to PeopleSoft processes that failed because they cannot allocate temporary tablespace because somebody else has consumed it.  This treated the symptom rather than the cause.  This system has a number of other Oracle database users who are have read-only access to the PeopleSoft data to perform adhoc queries.  These users all share the one temporary tablespace.  Occasionally, a query will be submitted that runs for many hours, writing many gigabytes of data to the temporary tablespace, when it would have been better to terminate the process
  • Another system has 64 GB in the PSTEMP temporary tablespace used by SYSADM.  All other users already use another temporary tablespace, but PeopleSoft processes sometimes still fail because most of the temporary tablespace has been consumed by an adhoc PS/Query process, and there is nothing left for other processes. This system also has other Oracle database users with read-only access, but here they use the default TEMP temporary tablespace.
If a PeopleSoft system has database users executing adhoc queries, then allocating those users to separate temporary tablespace is a sensible first step.

However, in this document I suggest going further.  I propose switching some PeopleSoft processes to use a different temporary tablespace.  Regular PeopleSoft processing will continue to use the first temporary tablespace, but adhoc queries will use the second temporary tablespace.  Thus, the first temporary tablespace can be sized to cater for normal processes safe in the knowledge that it won’t be consumed by adhoc queries and you won’t get failures due to space errors.  Meanwhile, the second tablespace can be limited to a reasonable size  and queries that make unreasonable demands on the temporary tablespace will error.

I am going to exploit two features:
  • When a session sets CURRENT_SCHEMA to another schema it uses the temporary tablespace assigned to that schema rather than its own.
  • From PeopleTools 8.51 you can direct read-only activity via a second connection to a standby database. If you are using Oracle Active Data Guard you must configure something that looks like a second PeopleSoft database in another schema, but which actually is composed of database synonyms that point to the first schema.
To make PeopleSoft process use an alternative temporary tablespace:
  • Create a second schema (I'll call it SYSADMRP) in the same database, and specify a different temporary tablespace for the user.
  • Create synonyms in the second schema for every table and view in the PeopleSoft (SYSADM) schema.
If you are not using Active DataGuard or are below PeopleTools 8.51 then you can set CURRENT_SCHEMA with two triggers.
  • Create an AFTER LOGON trigger that will set CURRENT_SCHEMA to SYSADM for PSQRYSRV query server processes only.

CREATE OR REPLACE TRIGGER sysadm.psqrysrv
AFTER LOGON
ON sysadm.schema
DECLARE
  l_module VARCHAR2(64);
BEGIN
  SELECT sys_context('USERENV', 'MODULE') 
  INTO   l_module
  FROM   dual;

  IF UPPER(l_module) LIKE 'PSQRYSRV%' THEN --then this is a PSQRYSRV session
    EXECUTE IMMEDIATE 'ALTER SESSION SET CURRENT_SCHEMA=SYSADMRP';
  END IF;
EXCEPTION WHEN NO_DATA_FOUND THEN NULL;
END;
/ 
  • Create another trigger to set current schema for the application engine process that runs scheduled queries (you might want to add others to this list).

CREATE OR REPLACE TRIGGER sysadm.set_current_schema
BEFORE UPDATE OF runstatus ON sysadm.psprcsrqst
FOR EACH ROW
WHEN (  (new.runstatus = '7' OR old.runstatus != '7') --if starting or terminating
     AND new.prcsname IN('PSQUERY')) --restrict to certain programs
DECLARE
BEGIN
  IF :new.runstatus = '7' THEN --if starting set alternative schema
    EXECUTE IMMEDIATE 'ALTER SESSION SET CURRENT_SCHEMA=SYSADMRP';
  ELSE --when process terminates reset to standard schema in case this is a PSAESRV process
    EXECUTE IMMEDIATE 'ALTER SESSION SET CURRENT_SCHEMA=SYSADM';
  END IF;
END;
/

If you are using at least PeopleTools 8.51, you don't need these triggers.  Instead you can configure the standby connection but to the same database
  • PS/Queries will always use the standby connection and hence the alternative tablespace.  
  • Batch processes can be marked as read only to make them connect to the standby connection. Remember that you must use PSAESRV processes.
  • If you want to make specific PeopleSoft components use the alternative temporary tablespace then you can only do this by perverting the PeopleTools Active Data Guard support and marking components as read only.

Conlusion

Now, you can choose an appropriate size for the one temporary tablespaces that will be sufficient for the regular operation of the application.  Adhoc queries will use alternative temporary tablespace.  You might choose to set a temporary tablespace size that may still cause queries to fail with a temproray tablespace error, but at least that won’t cause business-as-usual processes to crash.

You could even choose to run with three temporary tablespaces, one for PeopleSoft processes, one for PeopleSoft queries, and one for adhoc users accessing the database directly.

2 comments:

Gasparotto Nicolas said...

Hi David,
Kind of loopback, nice one, even though tricky.
In the linked document, shouldn't psdbowner.dbname (HCM91REP), tns entry (HCMRP) and StandbyDBName (HCM91) be identical to make all the "standby" connection use (pages 13-14)?
I think you also should add a link to your api code (http://www.go-faster.co.uk/scripts/psftapi.sql).

Regards,

Nicolas.

David Kurtz said...

After futher checking and testing, the second database name and TNS name (HCM91REP) is not required at all. The second schema (SYSADMRP) is selected by the second access profile which is associated with the StandbyUserId (PSAPPS2). So the StandbyDBName (HCM91) should be the same as DBName. Document updated.