Thursday, January 30, 2014

Implementing Deferred Segment Creation After an Upgrade

I have written previously about Deferred Segment Creation. Each empty table and its indexes use only 64Kb (assuming an 8Kb block size and locally managed tablespaces), but in a PeopleSoft there can be be tens of thousands of such tables and that adds up to a saving worth making.

If you are upgrading your database to 11gR2 , you might want to make sure that you are using it.  Deferred segment creation was introduced in Oracle and it became the default in  However, any table created in a previous version will have a physical segment.

This problem could affect any system, but it also manifests itself in PeopleSoft in a particular way.

When you run the alter scripts in PeopleTools a table may be recreated.  If it is a regular table (record type 0) then the CREATE TABLE command will not specify a segment creation clause and so the segment creation will be deferred until rows are inserted.

However, from PeopleTools 8.51, Application Designer uses the Oracle delivered DBMS_METADATA package to extract the DDL to recreate the object from the actual object.  However, this behaviour only occurs for Temporary working storage tables (record type 7).  Yes, these are exactly the tables that would benefit most from deferred segment creation because in many systems there are many unused temporary table instances.  If table was created under a version of the database prior to then the segment will exist and DBMS_METADATA will generate the DDL with the SEGMENT CREATION IMMEDIATE clause. 

-- Create temporary table 
You can use DBMS_SPACE_ADMIN.DROP_EMPTY_SEGMENTS to remove the segments for any empty tables (and their indexes) for which the segment has been previously created.  There would be no harm in simply running this program for every table in the system.  If there are rows then DBMS_SPACE_ADMIN will take no action.

The following script identifies candidate tables where the statistics suggest that there are no rowa or where there are no statistics.  I am indebted to Tim Hall for the idea for this tip.

set serveroutput on 
 FOR i IN (
  SELECT owner, table_name
  FROM   all_tables
  WHERE  owner = 'SYSADM'
  AND    segment_created = 'YES'
  AND    temporary = 'N'
  AND   (num_rows = 0 OR num_rows IS NULL)
  dbms_space_admin.drop_empty_segments (
    schema_name    => i.owner,
    table_name     => i.table_name);
As this package drops the empty segments, the SEGMENT_CREATED column on USER_TABLES changes to NO and if you were to extract the DDL with DBMS_METADATA the SEGMENT CREATION clause would have changed to DEFERRED.

As soon as any data is inserted, the segment is created, SEGMENT_CREATED changes to YES and the DDL generated by DBMS_METADATA would have SEGMENT CREATION IMMEDIATE.

The result is that 64Kb of space (assuming a block size of 8Kb) will be freed up for each empty table and index segment that is dropped. Your mileage may vary, but in my demo HR database that is over 20000 tables and 25000 indexes. 2.7Gb isn't a vast amount these days, but it is an easy win.

Added 1.2.2014:
To answer Noons' question below.  So long as the table or partition doesn't have any rows, the segment will be dropped it will as if the segment creation had been deferred.  You don't have to do anything special to the table.  There is no problem applying this to any empty tables create with their segments.  Here is a simple test with my results on

I will create a table and I have explicitly created the segment immediately, then I insert a row, commit the insert and delete the row.  I haven't even bothered to commit the delete.
SQL> create table t(a number) segment creation immediate;
SQL> insert into t values(42);
SQL> commit;
SQL> delete from t;
SQL> select segment_type, segment_name, tablespace_name from user_Segments where segment_name = 'T';

------------------ --------------- ------------------------------
TABLE              T               PSDEFAULT

SQL> select table_name, segment_created from user_tables where table_name = 'T';

TABLE_NAME                     SEG
------------------------------ ---
T                              YES

SQL> select dbms_metadata.get_ddl('TABLE','T') from dual;

   ( "A" NUMBER

So, at the moment the segment exists, it has had rows in it, but they have been deleted and the table is empty. If I run DBMS_SPACE_ADMIN.DROP_EMPTY_SEGMENTS the segment is dropped.

SQL> execute dbms_space_admin.drop_empty_segments (user,'T');
SQL> select segment_type, segment_name, tablespace_name from user_Segments where segment_name = 'T';

no rows selected

SQL> select table_name, segment_created from user_tables where table_name = 'T';

TABLE_NAME                     SEG
------------------------------ ---
T                              NO

SQL> select dbms_metadata.get_ddl('TABLE','T') from dual;

   ( "A" NUMBER

Friday, January 03, 2014

Date to Timestamp Conversion during PeopleTools Upgrade

This blog posting describes a script to convert Oracle date columns to Timestamps as used from PeopleTools 8.50 but only rebuilding those indexes that reference those columns, rather than drop and recreate every index in the system, thus producing a significant saving of time during the upgrade.

(A longer version of this article is available on my website)

I am working on a PeopleSoft upgrade project.  We are going from PeopleTools 8.49 to 8.53.  One of the things that happens is that some date columns in the Oracle database become timestamps.

Timestamps were introduced by Oracle in version 10g of the database, and provide the ability to store times accurate to the nanosecond (although the default is microsecond). Dates are accurate to the whole second.

There are 3 types of temporal column in PeopleSoft as defined on PSDBFIELD.  Prior to PeopleTools 8.50 they all become Oracle date columns in the database.  However, from PeopleTools 8.50; Time and DateTime fields are built as TimeStamp columns.if bit 5 of PSSTATUS.DATABASE_OPTIONS (value 32) is set.

PeopleTools Field Type
Database Column Type
PeopleTools <= 8.49 PeopleTools >= 8.50

Timestamps must be handled differently to dates in SQL.  Some date arithmetic must be done differently, in particular the difference between two timestamps is a timestamp rather than a number of days.  Therefore this setting also controls how PeopleCode date macros expand on Oracle.

During the upgrade, PeopleSoft Change Assistant simply alters all the Time and DateTime columns from dates to timestamps.  This generally works well.  The data value doesn't appear to get longer, so the block doesn't run out of room leading to row migration, and so it isn't necessary to rebuild every table that is affected.

However, there are some limitations. If the column being converted to a timestamp falls into one of the following categories you will get an error.
  • The column is a key column in a function-based index.
  • The table or index is partitioned by the column.
The functional key index issue has not affected many customers because the upgrade template drops all the indexes before altering the tables and rebuilding them again.

However, dropping and recreating all these indexes can be very time consuming and increases the duration of the outage required to perform the upgrade.  This has been my incentive to find a better way.

Function-Based Indexes
PeopleSoft Application Designer defines some key and search fields as descending.  The rows in components and the results of search dialogue are sorted on the key fields in the order specified.  Application Designer then indexes these columns in descending order (prior to PeopleTools 8 and since PeopleTools 8.47).  If any column in an Oracle index is in descending order the index is created as a function-based index.  Consequently, there can be a lot of descending indexes in a PeopleSoft system!  HR systems are particularly affected because many tables are effective-dated, and the field EFFDT is usually a descending key field.

It is not possible to alter a column to a timestamp if it appears anywhere in a function-based index. You get the following error:
ORA-30556: functional index is defined on the column to be modified 

Partitioning is not something that you usually encounter in a vanilla PeopleSoft system, but it can be added by customisation.  You generate the necessary DDL yourself if you want to use it. However, from PeopleTools 8.51 Application Designer will preserve existing partitioning.

In the system on which I am working, when partitioned the audit tables by AUDIT_STAMP which is a DateTime field.
ORA-14060: data type or length of an table partitioning column may not be changed 
We have had no alternative but to rebuild these tables and repopulate the data. This has also dealt with all locally partitioned indexes.

We have also found that we have one global index partitioned on a timestamp.
ORA-14061: data type or length of an index partitioning column may not be changed 
We also have had to drop this index in order to alter the table.

My Approach
We have had no alternative but to rebuild and repopulate our partitioned audit tables which are partitioned by a DateTime field.  However, that is what we did when we first partitioned them.  The scripts are very similar to those generated by Application Designer.  The table is renamed, a new one is built, and the data is copied.  In our case these scripts are built with a PL/SQL utility.  This also addressed the need to rebuild the locally partitioned indexes..

To minimize the number of indexes which must be rebuilt I have written a PL/SQL script ( that:
  • identifies the indexes that need to be dropped.
  • captures the DDL to recreate the indexes using DBMS_METADATA and stores it in a table,
  • drops the indexes,
  • alters the columns that cannot be altered with the index in place,
  • recreates the index.
The script successfully handles partitioned function-based indexes.

On this particular HR system we only rebuilt about 400 indexes instead of over 10000. Now the standard PeopleSoft upgrade template can be run without dropping or recreating any further indexes.

Thursday, January 02, 2014

Minimum Number of Recycling Server Processes

When I rebuilt my demo system (some while ago) with PeopleTools 8.52, I noticed a new message generated by ubbgen in PeopleTools 8.52 when the minimum number of recycling servers is set to 1.

To avoid loss of service, configure Min instance to at least 2.

What Produces the Message?
ubbgen is the PeopleSoft utility that merges the template file (psappsrv.ubx) with the configuration file (psappsrv.cfg) file to produce the Tuxedo configuration file (psappsrv.ubb) and the environment file (psappsrv.env). It is invoked by psadmin during Tuxedo domain configuration.
ubbgen -t psappsrv.ubx -c psappsrv.cfg -o psappsrv.ubb -v psappsrv.val -q y -u PUBSUB=n/QUICKSRV=n/QUERYSRV=n/JOLT=y/JRAD=n/DBGSRV=n/RENSRV=n/MCF=n/PPM=n/ANALYTICSRV=n
The message is produced at this time.

Recycling Servers
Several servers in a PeopleSoft application Server domain recycle after they have handled a number of services. Recycling is a PeopleSoft behaviour and not a Tuxedo behaviour.  It is controlled by the Recycle Count parameter in the PeopleSoft configuration file (psappsrv.cfg).  This parameter is not referenced in the template file (psappsrv.ubx).

; Settings for PSAPPSRV

; UBBGEN settings
Min Instances=2
Max Instances=3
Service Timeout=0

; Number of services after which PSAPPSRV will automatically restart.
; If the recycle count is set to zero, PSAPPSRV will never be recycled.
; The default value is zero.
; Dynamic change allowed for Recycle Count
Recycle Count=1000

PeopleSoft first started using BEA Tuxedo (as it was then) in PeopleTools 6 to remote call Cobol processes in the Financials product.  The Application Server was introduced in PeopleTools 7.  PSAPPSRV had recycling from the first release.  Legend has it that the engineers at Tuxedo where horrified when they heard that PeopleSoft had introduced recycling to resolve problems created by dynamic memory allocation and deallocation by the Panel Processor (now known as the component Processor).

Tuxedo servers are supposed to be robust, long lived and not require to be regularly restarted.  Hence the server restart functionality in Tuxedo is only designed to be invoked in the rare occasions when a server process crashes.  Server processes are started by the Restart Server (restartsrv), and only one process can be started concurrently.

The minimum of 2 applies to the following servers because they can both recycle and be configured to spawn additional instances on demand PSAPPSRV, PSANALYTICSRV, PSSAMSRV, PSQCKSRV, PSQRYSRV, PSPUBHND, PSSUBHND, PSBRKHND.  In the delivered configuration file for the developer domain, recycling is disabled for several servers by setting the recycle count to zero.  However, the message is produced by ubbgen irrespective of the value of recycle count.

The message handler servers can be set to have just a single instance, without producing any warning.  They only consume messages from the dispatcher processes so their temporary disappearance will not cause user errors.

What Happens When The Only Server Recycles?
Tuxedo server processes consume service requests placed on queues.  When a server starts up, it advertises its services on the Bulletin Board.  Tuxedo processes that submit requests (mostly the JSH processes, but also the message dispatcher processes, the Process Scheduler) look up on the Bulletin Board where a service is advertised and place it on the appropriate queue.

When a server process performs an orderly shutdown (as it does during a recycle) it removes the adverts for its services (the command is unadvertise).  If a process crashes the Bulletin Board Liaison process (BBL) detects the crash and cleans the Bullentin Board. When all services advertised on a queue have been unadvertised, the queue is also removed from the Bulletin Board.  If the process submitting the service request cannot find any server advertising a service it generates an error.  
074001.GO-FASTER-6!JSH.3124.5736.-2: JOLT_CAT:1043: "ERROR: tpacall() call failed, tperrno = 6"
This is why the minimum is 2.  If you recycled the only server process, it is possible for someone to produce this error (see also Minimum Number of Application Server Processes).

Should I set the minimum higher than 2?
The number of services handled by different server processes on the same queue is usually uneven because the service is handled by the first free server.  Therefore it is rare for the processes will reach the recycle count simultaneously, but it can still happen.  Even in a quiet system that doesn't have sufficient activity to justify 3 PSAPPSRVs, I prefer to set the minimum number of servers to at least 3. 

NB: If the debugger process is enabled then PSADMIN will force the minimum and maximum number of PSAPPSRV processes to at least 2.  ubbgen will actually update psappsrv.cfg.
Warning:  PSAPPSRV Min Instances too small, setting to 2 for debugger.