overview statistics in cms prd / non-prd environments

California State University

Common Management Systems

TUG Session: April 21, 2005 1

Overview Statistics inCMS PRD / Non-PRD Environments




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




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_




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.




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:





Where are statistics stored? Column Level Statistics

DBA_TAB_COLUMNS DBA_TAB_COL_STATISTICS DBA_PART_COL_STATISTICS DBA_SUBPART_COL_STATIS

TICS

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:


Note: The last three views extract statistics from DBA_TAB_COLUMNS.




How to gather Statistics?

ANALYZE statement

DBMS_UTILITY.ANALYZE_SCHEMA procedure

DBMS_STATS package

Statistics gathering methods:




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




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




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




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




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:




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




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;




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





UNIVIEW Main Menu

StatRanger





CBO Statistics Gathering Exceptions menu option:





CBO Statistics Gathering Exceptions:





CBO Audit Events menu option:





CBO Statistic Gathering Events menu option:





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”





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”




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.




Overview Statistics inCMS PRD / Non-PRD Environments

Questions?

overview statistics in cms prd / non-prd environments

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