1. California State University Common Management Systems TUG Session: April 21, 2005 1 Overview Statistics in CMS PRD / Non-PRD Environments

2. TUG Session: April 21, 2005 2 California State University Common Management Systems What Do Statistics Do?  Cost Base Optimizer (CBO) Utilize statistics Oracle and PeopleSoft Recommended CBO CMS implemented CBO in PRD/RPT and non-PRD environments To execute any SQL statement, Oracle optimizer has to derive an 'execution plan'. The execution plan of a query is a description of how Oracle will implement the retrieval of data to satisfy a given SQL statement.  Rule Base Optimizer (RBO) Ignore statistics Oracle de-support RBO on release 10g

3. TUG Session: April 21, 2005 3 California State University Common Management Systems Where are statistics stored?  Three levels of statistics: table, index, column  Statistics stored into Oracle data dictionary in tables own by SYS account  Views created on these tables to retrieve data more easily  Views prefixed with DBA_ or ALL_ or USER_

4. TUG Session: April 21, 2005 4 California State University Common Management Systems Where are statistics stored? Table Level Statistics  DBA_ALL_TABLES  DBA_OBJECT_TABLES  DBA_TABLES  DBA_TAB_PARTITIONS  DBA_TAB_SUBPARTITIONS Table level statistics can be retrieved from:  NUM_ROWS  BLOCKS  EMPTY_BLOCKS*  AVG_SPACE*  CHAIN_CNT*  AVG_ROW_LEN  AVG_SPACE_FREELIST_BLOCKS  NUM_FREELIST_BLOCKS  SAMPLE_SIZE  LAST-ANALYZED  GLOBAL_STATS  USER_STATS Columns to look at are: * Statistics gathered by ANALYZE statement.

5. TUG Session: April 21, 2005 5 California State University Common Management Systems Where are statistics stored? Index Level Statistics  DBA_INDEXES  DBA_IND_PARTITIONS  DBA_IND_SUBPARTITIONS  BLEVEL  LEAF_BLOCKS  DISTINCT_KEYS  AVG_LEAF_BLOCKS_PER_KEY  AVG_DATA_BLOCKS_PER_KEY  CLUSTERING_FACTOR  SAMPLE_SIZE  LAST_ANALYZED  GLOBAL_STATS  USER_STATS  PCT_DIRECT_ACCESS Index level statistics can be retrieved from: Columns to look at are:

6. TUG Session: April 21, 2005 6 California State University Common Management Systems Where are statistics stored? Column Level Statistics  DBA_TAB_COLUMNS  DBA_TAB_COL_STATISTICS  DBA_PART_COL_STATISTICS  DBA_SUBPART_COL_STATISTI CS  NUM_DISTINCT  LOW_VALUE  HIGH_VALUE  DENSITY  NUM_NULLS  AVG_COL_LEN  NUM_BUCKETS  SAMPLE_SIZE  LAST_ANALYZED  GLOBAL_STATS  USER_STATS Column level statistics can be retrieved from: Columns to look at are: Note: The last three views extract statistics from DBA_TAB_COLUMNS.

7. TUG Session: April 21, 2005 7 California State University Common Management Systems How to gather Statistics?  ANALYZE statement  DBMS_UTILITY.ANALYZE_SCHEMA procedure  DBMS_STATS package Statistics gathering methods:

8. TUG Session: April 21, 2005 8 California State University Common Management Systems How to gather Statistics? ANALYZE statement  Gathers statistics on table/indexes and columns histograms  Collect non-optimizer statistics: Validate the structure of an index partition, table/table partition, index-organized table, cluster, or object reference Identify migrated and chained rows of a table or cluster Collect information on freelist blocks

9. TUG Session: April 21, 2005 9 California State University Common Management Systems How to gather Statistics? ANALYZE statement  Estimate statistics: ANALYZE TABLE tablename ESTIMATE STATISTICS SAMPLE 30 PERCENT;  Compute statistics: ANALYZE TABLE tablename COMPUTE STATISTICS; Note: The above ANALYZE statements will gather statistics for table, indexes and histograms on ALL columns for the table and it will cause performance issues with CMS automated gather stats (StatRanger) Oracle document does not recommend using the ANALYZE statement to gather optimizer statistics in 8i/9i

10. TUG Session: April 21, 2005 10 California State University Common Management Systems How to gather Statistics? DBMS_UTILITY.ANALYZE_SCHEMA  Run ANALYZE statement on each table in the specified schema  Gathers statistics on table, all indexes, histogram on ALL columns (default bucket size 75) Note: The DBMS_UTILITY.ANALYZE_SCHEMA procedure will cause performance issues with CMS automated gather stats process Oracle document does not recommend using the DBMS_UTILITY.ANALYZE_SCHEMA procedure to gather optimizer statistics in 8i/9i

11. TUG Session: April 21, 2005 11 California State University Common Management Systems How to gather Statistics? DBMS_STATS package  Generate and manage statistics only for cost-based optimization  Collect, delete, modify, view, export, import statistics and gather stale tables  Gather only statistics for database objects that have impact on the optimizer  Set or get statistics  Transfer statistics  Gather statistics in parallel Note: CMS uses DBMS_STATS package to gather optimizer statistics on PRD/RPT, non-PRD instances

12. TUG Session: April 21, 2005 12 California State University Common Management Systems How to gather Statistics? Oracle no longer enhance the ANALYZE statement and DBMS_UTILITY.ANALYZE_SCHEMA procedure Oracle recommended DBMS_STATS package to collect optimizer statistics on 8i/9i instances The cost-based optimizer, which depends upon statistics, will eventually use only statistics that have been collected by DBMS_STATS Note:

13. TUG Session: April 21, 2005 13 California State University Common Management Systems Checking for Stale Statistics  SYS.MON_MODS$ table keeps track of modifications to tables with MONITORING column=YES  MONITORING column tracks the number of INSERT, UPDATE, and DELETE operations for the tables since the last time statistics were gathered  DBA_TAB_MODIFICATIONS, ALL_TAB_MODIFICATIONS, or USER_TAB_MODIFICATIONS views identify tables with stale statistics Note: CMS uses DBMS_STATS package and MONITORING to gather stale tables every 4 hours via Oracle job

14. TUG Session: April 21, 2005 14 California State University Common Management Systems Checking for Stale Statistics Set pagesize 100 Set linesize 120 COL NUM_ROWS FORMAT 99,999,999 HEADING 'Num Row' COL table_name FORMAT a20 HEADING 'Table Name' COL STALE FORMAT 999.999 HEADING 'Stale %' Sample SQL script, which list tables with stale statistics: SELECT b.table_name, TO_CHAR(b.LAST_ANALYZED, 'DD-MON-YY HH24:MI') Last_analyzed, ((a.INSERTS + a.UPDATES + a.DELETES)/(b.NUM_ROWS))*100 STALE, a.INSERTS, a.UPDATES, a.DELETES, b.NUM_ROWS FROM sys.dba_tab_modifications a, dba_tables b where a.table_name= b.table_name;

15. TUG Session: April 21, 2005 15 California State University Common Management Systems How CMS Gather Statistics  UNIVIEW application Centralize the management of the utilities including the CBO statistics gathering (StatRanger) Repository for CBO statistics gathering events by CBO_STATS package Use Oracle application form server - RCAT9P instance  StatRanger CMS central can define the CBO methods, global CBO exceptions, CBO exceptions for tables in each instance CMS central can manually force refresh statistics, reload old statistics, transfer statistics for tables and view the audit of the statistics gathering events Audit all changes to CBO exception rules

16. TUG Session: April 21, 2005 16 California State University Common Management Systems How CMS Gather Statistics UNIVIEW Main Menu StatRanger

17. TUG Session: April 21, 2005 17 California State University Common Management Systems How CMS Gather Statistics CBO Statistics Gathering Exceptions menu option:

18. TUG Session: April 21, 2005 18 California State University Common Management Systems How CMS Gather Statistics CBO Statistics Gathering Exceptions:

19. TUG Session: April 21, 2005 19 California State University Common Management Systems How CMS Gather Statistics CBO Statistics Gathering Exceptions:

20. TUG Session: April 21, 2005 20 California State University Common Management Systems How CMS Gather Statistics CBO Statistics Gathering Exceptions:

21. TUG Session: April 21, 2005 21 California State University Common Management Systems How CMS Gather Statistics CBO Audit Events menu option:

22. TUG Session: April 21, 2005 22 California State University Common Management Systems How CMS Gather Statistics CBO Statistic Gathering Events menu option:

23. TUG Session: April 21, 2005 23 California State University Common Management Systems How CMS Gather Statistics Note: 1. CMS automated the statistics gathering process by executing the CBO_STATS.GATHER_STATS procedure every 4 hours via Oracle job on each instance 2. The default CBO method option for gathering statistics in CMS environments is “FOR TABLE FOR ALL INDEXES FOR ALL INDEXED COLUMNS SIZE 75”

24. TUG Session: April 21, 2005 24 California State University Common Management Systems How CMS Gather Statistics  Gather statistics on tables which have stale statistics >= 10%  Gather statistics on tables/indexes which have no statistics  Turn on MONITORING for all SYSADM tables which have MONITORING=NO  Drop statistics for tables which have CBO method option as NONE  Audit the CBO events in RCAT9P CBO_STATS.GATHER_STATS procedure: Note: If a table name does not exist in the global or local CBO exception lists, the default statistics gathering method is “FOR ALL INDEXED COLUMNS SIZE 75”

25. TUG Session: April 21, 2005 25 California State University Common Management Systems Why We Do It? CMS proactively gathers statistics for any SYSADM table/index, which have no statistics or stale statistics to improve PeopleSoft processes/queries performance.

26. TUG Session: April 21, 2005 26 California State University Common Management Systems Overview Statistics in CMS PRD / Non-PRD Environments Questions?