About Oracle Statistics
1. What are statistics?
Answer: Input to the Cost-Based Optimizer(CBO),Provide information on
User objects, Table, Partition,Subpartition ,Column ,Index, Index Partition, Index Subpartition, System, Dictionary , Memory structure(X$)
Statistics on a table are considered stale when more than STALE_PERCENT (default 10%) of the rows are changed (total number of inserts, deletes, updates) in the table.
Oracle monitors the DML activity for all tables and records it in the SGA.
The monitoring information is periodically flushed to disk, and is exposed in the *_TAB_MODIFICATIONS view.
2.Why do we care about statistics?
Poor statisitics usually lead to poor plans.
Collecting good quality stats is not straightforward
Collecting good quality stats may be time consuming.
Improving statistics quality improves the chance to find an optimal plan(usually)
The higher the sample the higher the accuracy
The higher the sample the longer is takes to collect
The longer it takes the less frequent we can collect fresh stats!
if your data changes frequently, we need to care about statistics.
if you have plenty of resources:
Gather statistics often and with a very large sample size.
If your resources are limited :
Use AUTO_SAMPLE_SIZE(11g)
Use a smaller sample size(try to avoid it)
If your data doesn't change frequently:
Gahter statistics less often and with a very large sample size.
---In 10g avoid AUTO_SAMPLE_SIZE
exec dbms_stats.gather_table_stats('owner', 'table_name', estimate_percent => NNN,granularity => “it depends”);
----In 11g use AUTO_SAMPLE_SIZE but keep an eye open.
exec dbms_stats.gather_table_stats('owner', 'table_name');About *_TAB_MODIFICATIONS
when querying *_TAB_MODIFICATIONS view you should ensure that you run DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO before doing so in order to obtain accurate results.
-- exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO; --
[oracle@oracle-db-19c ~]$
[oracle@oracle-db-19c ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Feb 2 09:37:33 2023
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL>
SQL>
SQL> select table_name,inserts,updates,deletes from dba_tab_modifications where table_name='emp';
no rows selected
SQL>
SQL>
SQL>
SQL> exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO;
PL/SQL procedure successfully completed.
SQL>
SQL> select table_name,inserts,updates,deletes from dba_tab_modifications where table_name='emp';
no rows selected
SQL> show user;
USER is "SYS"
SQL> Identify STALE STATS:
SQL> col owner format a30
SQL> col TABLE_NAME for a30
SQL> col PARTITION_NAME for a20
SQL> col SUBPARTITION_NAME for a20
SQL> select OWNER,TABLE_NAME,PARTITION_NAME,SUBPARTITION_NAME,NUM_ROWS,LAST_ANALYZED from DBA_TAB_STATISTICS where STALE_STATS='YES';
OWNER TABLE_NAME PARTITION_NAME SUBPARTITION_NAME NUM_ROWS LAST_ANALYZED
------------------------------ ------------------------------ -------------------- -------------------- ---------- ---------------
SYS SEG$ 5094 01-FEB-23
SYS IND$ 2885 29-JAN-23
SYS TAB$ 2219 31-JAN-23
SYS HISTGRM$ 62858 01-FEB-23
SYS PARTOBJ$ 275 29-JAN-23
SYS PROPS$ 43 01-FEB-23
SYS STATS_TARGET$ 792 01-FEB-23
SYS COL_USAGE$ 3398 01-FEB-23
SYS COL_GROUP_USAGE$ 13 01-FEB-23
SYS MON_MODS_ALL$ 228 01-FEB-23
SYS WRI$_OPTSTAT_OPR 16 01-FEB-23
SYS WRI$_OPTSTAT_OPR_TASKS 2620 01-FEB-23
SYS OPTSTAT_HIST_CONTROL$ 45 01-FEB-23
SYS OPT_FINDING$ 28 01-FEB-23
SYS OPT_DIRECTIVE_OWN$ 24 01-FEB-23
SYS OPT_DIRECTIVE$ 28 01-FEB-23
SYS EXP_OBJ$ 9 01-FEB-23
SYS EXP_STAT$ 47 01-FEB-23
SYS TABPART$ 352 01-FEB-23
SYS INDPART$ 233 01-FEB-23
SYS LOBFRAG$ 27 31-JAN-23
SYS WRI$_ADV_TASKS 92 01-FEB-23
SYS WRI$_ADV_PARAMETERS 6631 01-FEB-23
SYS WRI$_ADV_EXECUTIONS 97 01-FEB-23
SYS WRI$_ADV_EXEC_PARAMETERS 5 01-FEB-23
SYS WRI$_ADV_OBJECTS 171 01-FEB-23
SYS WRI$_ADV_FINDINGS 159 01-FEB-23
SYS WRI$_ADV_MESSAGE_GROUPS 609 31-JAN-23
SYS WRI$_ADV_ADDM_TASKS 86 01-FEB-23
SYS WRI$_ADV_ADDM_INST 86 01-FEB-23
SYS WRI$_ADV_ADDM_FDG 140 01-FEB-23
SYS WRI$_ADV_ADDM_TODO 0 01-FEB-23
SYS SCHEDULER$_CLASS 15 22-JAN-23
SYS SCHEDULER$_JOB 25 01-FEB-23
SYS SCHEDULER$_WINDOW 9 01-FEB-23
SYS SCHEDULER$_WINDOW_DETAILS 5 01-FEB-23
SYS WRI$_DBU_CPU_USAGE_SAMPLE 2 01-FEB-23
SYS KET$_AUTOTASK_STATUS 1 01-FEB-23
SYS KET$_CLIENT_TASKS 3 01-FEB-23
SYS WRI$_SQLMON_USAGE 1 01-FEB-23
SYS WRH$_DATAFILE 48 31-JAN-23
SYS WRH$_IOSTAT_FUNCTION 540 01-FEB-23
SYS WRH$_IOSTAT_FILETYPE 828 01-FEB-23
SYS WRH$_IOSTAT_DETAIL 861 01-FEB-23
SYS WRH$_SQLSTAT 3678 01-FEB-23
SYS WRH$_SQLTEXT 863 01-FEB-23
SYS WRH$_SQL_SUMMARY 140 01-FEB-23
SYS WRH$_SQL_BIND_METADATA 3980 01-FEB-23
SYS WRH$_OPTIMIZER_ENV 459 01-FEB-23
SYS WRH$_SYSTEM_EVENT 5189 01-FEB-23
SYS WRH$_CON_SYSTEM_EVENT 9083 01-FEB-23
SYS WRH$_BG_EVENT_SUMMARY 4088 01-FEB-23
SYS WRH$_CHANNEL_WAITS 144 01-FEB-23
SYS WRH$_WAITSTAT 2790 01-FEB-23
SYS WRH$_ENQUEUE_STAT 3867 01-FEB-23
SYS WRH$_LATCH 40090 01-FEB-23
SYS WRH$_LATCH_MISSES_SUMMARY 2373 01-FEB-23
SYS WRH$_EVENT_HISTOGRAM 49062 01-FEB-23
SYS WRH$_MUTEX_SLEEP 1519 01-FEB-23
SYS WRH$_LIBRARYCACHE 1013 01-FEB-23
SYS WRH$_DB_CACHE_ADVICE 785 01-FEB-23
SYS WRH$_BUFFER_POOL_STATISTICS 36 01-FEB-23
SYS WRH$_ROWCACHE_SUMMARY 2432 01-FEB-23
SYS WRH$_SGA 144 01-FEB-23
SYS WRH$_SGASTAT 1200 01-FEB-23
SYS WRH$_PGASTAT 572 01-FEB-23
SYS WRH$_PROCESS_MEMORY_SUMMARY 372 01-FEB-23
SYS WRH$_RESOURCE_LIMIT 792 01-FEB-23
SYS WRH$_SHARED_POOL_ADVICE 930 01-FEB-23
SYS WRH$_SQL_WORKAREA_HISTOGRAM 268 01-FEB-23
SYS WRH$_PGA_TARGET_ADVICE 504 01-FEB-23
SYS WRH$_SGA_TARGET_ADVICE 213 01-FEB-23
SYS WRH$_INSTANCE_RECOVERY 36 01-FEB-23
SYS WRH$_RECOVERY_PROGRESS 1 29-JAN-23
SYS WRH$_THREAD 36 01-FEB-23
SYS WRH$_SYSSTAT 77368 01-FEB-23
SYS WRH$_CON_SYSSTAT 23139 01-FEB-23
SYS WRH$_SYS_TIME_MODEL 1178 01-FEB-23
SYS WRH$_CON_SYS_TIME_MODEL 6030 01-FEB-23
SYS WRH$_OSSTAT 950 01-FEB-23
SYS WRH$_PARAMETER 18782 01-FEB-23
SYS WRH$_MVPARAMETER 273 01-FEB-23
SYS WRH$_UNDOSTAT 178 01-FEB-23
SYS WRH$_SEG_STAT 3005 01-FEB-23
SYS WRH$_SEG_STAT_OBJ 570 01-FEB-23
SYS WRH$_SYSMETRIC_HISTORY 37467 01-FEB-23
SYS WRH$_SYSMETRIC_SUMMARY 5796 01-FEB-23
SYS WRH$_CON_SYSMETRIC_SUMMARY 5508 01-FEB-23
SYS WRH$_ACTIVE_SESSION_HISTORY 6002 01-FEB-23
SYS WRH$_TABLESPACE_STAT 591 01-FEB-23
SYS WRH$_LOG 108 01-FEB-23
SYS WRH$_TABLESPACE 42 31-JAN-23
SYS WRH$_TABLESPACE_SPACE_USAGE 636 01-FEB-23
SYS WRH$_SERVICE_NAME 14 01-FEB-23
SYS WRH$_SERVICE_STAT 6612 01-FEB-23
SYS WRH$_SERVICE_WAIT_CLASS 1018 01-FEB-23
SYS WRI$_SCH_CONTROL 1 01-FEB-23
SYS WRI$_SCH_VOTES 7 01-FEB-23
SYS WRH$_RSRC_CONSUMER_GROUP 228 01-FEB-23
SYS WRH$_RSRC_PLAN 157 01-FEB-23
SYS WRH$_RSRC_METRIC 422 01-FEB-23
SYS WRH$_RSRC_PDB_METRIC 144 01-FEB-23
SYS WRH$_MEM_DYNAMIC_COMP 792 01-FEB-23
SYS WRH$_DISPATCHER 36 01-FEB-23
SYS WRH$_SHARED_SERVER_SUMMARY 36 01-FEB-23
SYS WRM$_WR_USAGE 1 01-FEB-23
SYS WRM$_DATABASE_INSTANCE 5 01-FEB-23
SYS WRM$_SNAPSHOT 35 01-FEB-23
SYS WRM$_SNAPSHOT_DETAILS 3787 01-FEB-23
SYS WRM$_SNAP_ERROR 17 01-FEB-23
SYS WRM$_PDB_IN_SNAP 152 01-FEB-23
SYS WRM$_WR_CONTROL 1 01-FEB-23
SYS WRH$_PROCESS_WAITTIME 7155 01-FEB-23
SYS WRH$_SESS_NETWORK 2 29-JAN-23
SYS WRI$_OPTSTAT_HISTHEAD_HISTORY 18955 01-FEB-23
SYS WRI$_OPTSTAT_HISTGRM_HISTORY 109249 01-FEB-23
SYS WRH$_CON_SYSSTAT WRH$_CON_SYSSTAT_109 23139 01-FEB-23
3429351_138
SYS WRH$_CON_SYSTEM_EVENT WRH$_CON_SYSTEM_EVEN 9083 01-FEB-23
T_1093429351_138
SYS WRH$_PROCESS_WAITTIME WRH$_PROCESS_WAITTIM 7155 01-FEB-23
E_1093429351_138
SYS WRH$_SESS_NETWORK WRH$_SESS_NETWORK_10 2 29-JAN-23
93429351_138
SYS WRH$_SYSMETRIC_HISTORY WRH$_SYSMETRIC_HISTO 37467 01-FEB-23
RY_1093429351_138
SYS WRH$_TABLESPACE_STAT WRH$_TABLESPACE_STAT 591 01-FEB-23
_1093429351_138
SYS WRH$_OSSTAT WRH$_OSSTAT_10934293 950 01-FEB-23
51_138
SYS WRH$_SYS_TIME_MODEL WRH$_SYS_TIME_MODEL_ 1178 01-FEB-23
1093429351_138
SYS WRH$_SERVICE_WAIT_CLASS WRH$_SERVICE_WAIT_CL 1018 01-FEB-23
ASS_1093429351_138
SYS WRH$_EVENT_HISTOGRAM WRH$_EVENT_HISTOGRAM 49062 01-FEB-23
_1093429351_138
SYS WRH$_MVPARAMETER WRH$_MVPARAMETER_109 273 01-FEB-23
3429351_138
SYS WRM$_PDB_IN_SNAP WRM$_PDB_IN_SNAP_109 152 01-FEB-23
3429351_138
SYS WRH$_CON_SYS_TIME_MODEL WRH$_CON_SYS_TIME_MO 6030 01-FEB-23
DEL_1093429351_138
SYS WRP$_REPORTS_TIME_BANDS SYS_P901 27 01-FEB-23
SYS WRP$_REPORTS SYS_P921 26 01-FEB-23
SYS WRP$_REPORTS_DETAILS SYS_P922 26 01-FEB-23
SYS WRH$_SQLSTAT WRH$_SQLSTAT_1093429 3678 01-FEB-23
351_138
SYS WRH$_SYSTEM_EVENT WRH$_SYSTEM_EVENT_10 5189 01-FEB-23
93429351_138
SYS WRH$_WAITSTAT WRH$_WAITSTAT_109342 2790 01-FEB-23
9351_138
SYS WRH$_LATCH WRH$_LATCH_109342935 40090 01-FEB-23
1_138
SYS WRH$_LATCH_MISSES_SUMMARY WRH$_LATCH_MISSES_SU 2373 01-FEB-23
MMARY_1093429351_138
SYS WRH$_DB_CACHE_ADVICE WRH$_DB_CACHE_ADVICE 785 01-FEB-23
_1093429351_138
SYS WRH$_ROWCACHE_SUMMARY WRH$_ROWCACHE_SUMMAR 2432 01-FEB-23
Y_1093429351_138
SYS WRH$_SGASTAT WRH$_SGASTAT_1093429 1200 01-FEB-23
351_138
SYS WRH$_SYSSTAT WRH$_SYSSTAT_1093429 77368 01-FEB-23
351_138
SYS WRH$_PARAMETER WRH$_PARAMETER_10934 18782 01-FEB-23
29351_138
SYS WRH$_SEG_STAT WRH$_SEG_STAT_109342 3005 01-FEB-23
9351_138
SYS WRH$_SERVICE_STAT WRH$_SERVICE_STAT_10 6612 01-FEB-23
93429351_138
144 rows selected.
SQL>
SQL>
----
OR
----
SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where OWNER='&OWNER' AND STALE_STATS='YES';
Enter value for owner: SYS
old 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where OWNER='&OWNER' AND STALE_STATS='YES'
new 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where OWNER='SYS' AND STALE_STATS='YES'
OWNER TABLE_NAME LAST_ANALYZED STALE_STATS
------------------------------ ------------------------------ --------------- ---------------------
SYS WRH$_WAITSTAT 01-FEB-23 YES
SYS WRH$_SQL_SUMMARY 01-FEB-23 YES
SYS WRH$_LOG 01-FEB-23 YES
SYS STATS_TARGET$ 01-FEB-23 YES
SYS WRH$_ACTIVE_SESSION_HISTORY 01-FEB-23 YES
SYS WRH$_IOSTAT_DETAIL 01-FEB-23 YES
SYS WRH$_RSRC_PLAN 01-FEB-23 YES
SYS WRH$_CON_SYSMETRIC_SUMMARY 01-FEB-23 YES
SYS WRH$_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_MVPARAMETER 01-FEB-23 YES
SYS SCHEDULER$_WINDOW 01-FEB-23 YES
SYS OPT_DIRECTIVE$ 01-FEB-23 YES
SYS WRH$_INSTANCE_RECOVERY 01-FEB-23 YES
SYS SEG$ 01-FEB-23 YES
SYS WRH$_TABLESPACE 31-JAN-23 YES
SYS WRH$_PROCESS_MEMORY_SUMMARY 01-FEB-23 YES
SYS WRM$_SNAPSHOT 01-FEB-23 YES
SYS WRH$_SGA_TARGET_ADVICE 01-FEB-23 YES
SYS WRH$_SERVICE_STAT 01-FEB-23 YES
SYS WRH$_RSRC_METRIC 01-FEB-23 YES
SYS WRH$_SQL_WORKAREA_HISTOGRAM 01-FEB-23 YES
SYS WRH$_SGASTAT 01-FEB-23 YES
SYS WRH$_SQLSTAT 01-FEB-23 YES
SYS WRH$_PGASTAT 01-FEB-23 YES
SYS WRI$_ADV_TASKS 01-FEB-23 YES
SYS PARTOBJ$ 29-JAN-23 YES
SYS EXP_OBJ$ 01-FEB-23 YES
SYS PROPS$ 01-FEB-23 YES
SYS WRI$_OPTSTAT_OPR_TASKS 01-FEB-23 YES
SYS TABPART$ 01-FEB-23 YES
SYS WRH$_ROWCACHE_SUMMARY 01-FEB-23 YES
SYS WRH$_RSRC_CONSUMER_GROUP 01-FEB-23 YES
SYS WRH$_MEM_DYNAMIC_COMP 01-FEB-23 YES
SYS WRH$_SEG_STAT_OBJ 01-FEB-23 YES
SYS WRH$_SERVICE_WAIT_CLASS 01-FEB-23 YES
SYS WRH$_SYSSTAT 01-FEB-23 YES
SYS WRH$_SYSTEM_EVENT 01-FEB-23 YES
SYS WRM$_DATABASE_INSTANCE 01-FEB-23 YES
SYS WRH$_CON_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_TABLESPACE_SPACE_USAGE 01-FEB-23 YES
SYS WRH$_DATAFILE 31-JAN-23 YES
SYS WRH$_CHANNEL_WAITS 01-FEB-23 YES
SYS WRH$_DB_CACHE_ADVICE 01-FEB-23 YES
SYS WRH$_SHARED_SERVER_SUMMARY 01-FEB-23 YES
SYS WRH$_RSRC_PDB_METRIC 01-FEB-23 YES
SYS WRH$_SYSMETRIC_HISTORY 01-FEB-23 YES
SYS WRI$_ADV_ADDM_TASKS 01-FEB-23 YES
SYS KET$_CLIENT_TASKS 01-FEB-23 YES
SYS WRI$_ADV_OBJECTS 01-FEB-23 YES
SYS WRH$_ENQUEUE_STAT 01-FEB-23 YES
SYS WRH$_EVENT_HISTOGRAM 01-FEB-23 YES
SYS WRH$_CON_SYSTEM_EVENT 01-FEB-23 YES
SYS SCHEDULER$_WINDOW_DETAILS 01-FEB-23 YES
SYS WRH$_THREAD 01-FEB-23 YES
SYS OPT_DIRECTIVE_OWN$ 01-FEB-23 YES
SYS OPT_FINDING$ 01-FEB-23 YES
SYS OPTSTAT_HIST_CONTROL$ 01-FEB-23 YES
SYS WRH$_BUFFER_POOL_STATISTICS 01-FEB-23 YES
SYS SCHEDULER$_JOB 01-FEB-23 YES
SYS COL_GROUP_USAGE$ 01-FEB-23 YES
SYS COL_USAGE$ 01-FEB-23 YES
SYS WRH$_IOSTAT_FUNCTION 01-FEB-23 YES
SYS WRH$_OSSTAT 01-FEB-23 YES
SYS WRM$_PDB_IN_SNAP 01-FEB-23 YES
SYS WRM$_SNAP_ERROR 01-FEB-23 YES
SYS WRH$_LIBRARYCACHE 01-FEB-23 YES
SYS WRI$_ADV_ADDM_TODO 01-FEB-23 YES
SYS TAB$ 31-JAN-23 YES
SYS HISTGRM$ 01-FEB-23 YES
SYS WRH$_UNDOSTAT 01-FEB-23 YES
SYS MON_MODS_ALL$ 01-FEB-23 YES
SYS INDPART$ 01-FEB-23 YES
SYS WRH$_TABLESPACE_STAT 01-FEB-23 YES
SYS WRH$_PGA_TARGET_ADVICE 01-FEB-23 YES
SYS WRI$_ADV_EXEC_PARAMETERS 01-FEB-23 YES
SYS WRH$_LATCH_MISSES_SUMMARY 01-FEB-23 YES
SYS WRI$_OPTSTAT_HISTHEAD_HISTORY 01-FEB-23 YES
SYS WRH$_SEG_STAT 01-FEB-23 YES
SYS WRH$_SYSMETRIC_SUMMARY 01-FEB-23 YES
SYS WRI$_OPTSTAT_HISTGRM_HISTORY 01-FEB-23 YES
SYS WRI$_ADV_PARAMETERS 01-FEB-23 YES
SYS WRH$_OPTIMIZER_ENV 01-FEB-23 YES
SYS WRI$_ADV_FINDINGS 01-FEB-23 YES
SYS WRH$_RECOVERY_PROGRESS 29-JAN-23 YES
SYS EXP_STAT$ 01-FEB-23 YES
SYS WRH$_SQL_BIND_METADATA 01-FEB-23 YES
SYS WRH$_CON_SYSSTAT 01-FEB-23 YES
SYS SCHEDULER$_CLASS 22-JAN-23 YES
SYS WRH$_SGA 01-FEB-23 YES
SYS WRI$_OPTSTAT_OPR 01-FEB-23 YES
SYS WRH$_SESS_NETWORK 29-JAN-23 YES
SYS WRH$_SQLTEXT 01-FEB-23 YES
SYS WRH$_BG_EVENT_SUMMARY 01-FEB-23 YES
SYS WRI$_ADV_ADDM_FDG 01-FEB-23 YES
SYS LOBFRAG$ 31-JAN-23 YES
SYS IND$ 29-JAN-23 YES
SYS WRI$_ADV_ADDM_INST 01-FEB-23 YES
SYS WRH$_RESOURCE_LIMIT 01-FEB-23 YES
SYS WRM$_WR_CONTROL 01-FEB-23 YES
SYS WRI$_DBU_CPU_USAGE_SAMPLE 01-FEB-23 YES
SYS WRH$_PROCESS_WAITTIME 01-FEB-23 YES
SYS WRH$_MUTEX_SLEEP 01-FEB-23 YES
SYS WRH$_LATCH 01-FEB-23 YES
SYS WRH$_DISPATCHER 01-FEB-23 YES
SYS WRH$_IOSTAT_FILETYPE 01-FEB-23 YES
SYS WRH$_SHARED_POOL_ADVICE 01-FEB-23 YES
SYS WRH$_PARAMETER 01-FEB-23 YES
SYS KET$_AUTOTASK_STATUS 01-FEB-23 YES
SYS WRI$_ADV_EXECUTIONS 01-FEB-23 YES
SYS WRM$_WR_USAGE 01-FEB-23 YES
SYS WRI$_SCH_VOTES 01-FEB-23 YES
SYS WRI$_SCH_CONTROL 01-FEB-23 YES
SYS WRI$_ADV_MESSAGE_GROUPS 31-JAN-23 YES
SYS WRM$_SNAPSHOT_DETAILS 01-FEB-23 YES
SYS WRH$_SERVICE_NAME 01-FEB-23 YES
SYS WRI$_SQLMON_USAGE 01-FEB-23 YES
SYS WRH$_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_MVPARAMETER 01-FEB-23 YES
SYS WRH$_WAITSTAT 01-FEB-23 YES
SYS WRP$_REPORTS 01-FEB-23 YES
SYS WRH$_SGASTAT 01-FEB-23 YES
SYS WRH$_SQLSTAT 01-FEB-23 YES
SYS WRH$_SERVICE_STAT 01-FEB-23 YES
SYS WRP$_REPORTS_TIME_BANDS 01-FEB-23 YES
SYS WRH$_ROWCACHE_SUMMARY 01-FEB-23 YES
SYS WRH$_SERVICE_WAIT_CLASS 01-FEB-23 YES
SYS WRH$_CON_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_SYSSTAT 01-FEB-23 YES
SYS WRH$_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_EVENT_HISTOGRAM 01-FEB-23 YES
SYS WRH$_SYSMETRIC_HISTORY 01-FEB-23 YES
SYS WRH$_DB_CACHE_ADVICE 01-FEB-23 YES
SYS WRH$_CON_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_OSSTAT 01-FEB-23 YES
SYS WRP$_REPORTS_DETAILS 01-FEB-23 YES
SYS WRH$_TABLESPACE_STAT 01-FEB-23 YES
SYS WRM$_PDB_IN_SNAP 01-FEB-23 YES
SYS WRH$_LATCH_MISSES_SUMMARY 01-FEB-23 YES
SYS WRH$_SEG_STAT 01-FEB-23 YES
SYS WRH$_SESS_NETWORK 29-JAN-23 YES
SYS WRH$_CON_SYSSTAT 01-FEB-23 YES
SYS WRH$_PROCESS_WAITTIME 01-FEB-23 YES
SYS WRH$_LATCH 01-FEB-23 YES
SYS WRH$_PARAMETER 01-FEB-23 YES
144 rows selected.
SQL> Gather STATS
CASCADE => TRUE : Gather statistics on the indexes as well. If not used Oracle will determine whether to collect it or not.
DEGREE => 4: Degree of parallelism.
ESTIMATE_PERCENT => DBMS_STATS.AUTO_SAMPLE_SIZE : (DEFAULT) Auto set the sample size % for skew(distinct) values (accurate and faster than setting a manual sample size).
METHOD_OPT=> : For gathering Histograms:
FOR COLUMNS SIZE AUTO : You can specify one column between “” instead of all columns.
FOR ALL COLUMNS SIZE REPEAT : Prevent deletion of histograms and collect it only for columns already have histograms.
FOR ALL COLUMNS : Collect histograms on all columns.
FOR ALL COLUMNS SIZE SKEWONLY : Collect histograms for columns have skewed value should test skewness first
FOR ALL INDEXED COLUMNS : Collect histograms for columns have indexes only.
Database Level
Gathering statistics for all objects in database, cascade will include indexes
SQL>
SQL> show user;
USER is "SYS"
SQL> exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO;
PL/SQL procedure successfully completed.
SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES';
OWNER TABLE_NAME LAST_ANALYZED STALE_STATS
------------------------------ ------------------------------ --------------- ---------------------
SYS SEG$ 01-FEB-23 YES
SYS IND$ 29-JAN-23 YES
SYS TAB$ 31-JAN-23 YES
SYS HISTGRM$ 01-FEB-23 YES
SYS PARTOBJ$ 29-JAN-23 YES
SYS PROPS$ 01-FEB-23 YES
SYS STATS_TARGET$ 01-FEB-23 YES
SYS COL_USAGE$ 01-FEB-23 YES
SYS COL_GROUP_USAGE$ 01-FEB-23 YES
SYS MON_MODS_ALL$ 01-FEB-23 YES
SYS WRI$_OPTSTAT_OPR 01-FEB-23 YES
SYS WRI$_OPTSTAT_OPR_TASKS 01-FEB-23 YES
SYS OPTSTAT_HIST_CONTROL$ 01-FEB-23 YES
SYS OPT_FINDING$ 01-FEB-23 YES
SYS OPT_DIRECTIVE_OWN$ 01-FEB-23 YES
SYS OPT_DIRECTIVE$ 01-FEB-23 YES
SYS EXP_OBJ$ 01-FEB-23 YES
SYS EXP_STAT$ 01-FEB-23 YES
SYS TABPART$ 01-FEB-23 YES
SYS INDPART$ 01-FEB-23 YES
SYS LOBFRAG$ 31-JAN-23 YES
SYS WRI$_ADV_TASKS 01-FEB-23 YES
SYS WRI$_ADV_PARAMETERS 01-FEB-23 YES
SYS WRI$_ADV_EXECUTIONS 01-FEB-23 YES
SYS WRI$_ADV_EXEC_PARAMETERS 01-FEB-23 YES
SYS WRI$_ADV_OBJECTS 01-FEB-23 YES
SYS WRI$_ADV_FINDINGS 01-FEB-23 YES
SYS WRI$_ADV_MESSAGE_GROUPS 31-JAN-23 YES
SYS WRI$_ADV_ADDM_TASKS 01-FEB-23 YES
SYS WRI$_ADV_ADDM_INST 01-FEB-23 YES
SYS WRI$_ADV_ADDM_FDG 01-FEB-23 YES
SYS WRI$_ADV_ADDM_TODO 01-FEB-23 YES
SYS SCHEDULER$_CLASS 22-JAN-23 YES
SYS SCHEDULER$_JOB 01-FEB-23 YES
SYS SCHEDULER$_WINDOW 01-FEB-23 YES
SYS SCHEDULER$_WINDOW_DETAILS 01-FEB-23 YES
SYS WRI$_DBU_CPU_USAGE_SAMPLE 01-FEB-23 YES
SYS KET$_AUTOTASK_STATUS 01-FEB-23 YES
SYS KET$_CLIENT_TASKS 01-FEB-23 YES
SYS WRI$_SQLMON_USAGE 01-FEB-23 YES
SYS WRH$_DATAFILE 31-JAN-23 YES
SYS WRH$_IOSTAT_FUNCTION 01-FEB-23 YES
SYS WRH$_IOSTAT_FILETYPE 01-FEB-23 YES
SYS WRH$_IOSTAT_DETAIL 01-FEB-23 YES
SYS WRH$_SQLSTAT 01-FEB-23 YES
SYS WRH$_SQLTEXT 01-FEB-23 YES
SYS WRH$_SQL_SUMMARY 01-FEB-23 YES
SYS WRH$_SQL_BIND_METADATA 01-FEB-23 YES
SYS WRH$_OPTIMIZER_ENV 01-FEB-23 YES
SYS WRH$_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_CON_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_BG_EVENT_SUMMARY 01-FEB-23 YES
SYS WRH$_CHANNEL_WAITS 01-FEB-23 YES
SYS WRH$_WAITSTAT 01-FEB-23 YES
SYS WRH$_ENQUEUE_STAT 01-FEB-23 YES
SYS WRH$_LATCH 01-FEB-23 YES
SYS WRH$_LATCH_MISSES_SUMMARY 01-FEB-23 YES
SYS WRH$_EVENT_HISTOGRAM 01-FEB-23 YES
SYS WRH$_MUTEX_SLEEP 01-FEB-23 YES
SYS WRH$_LIBRARYCACHE 01-FEB-23 YES
SYS WRH$_DB_CACHE_ADVICE 01-FEB-23 YES
SYS WRH$_BUFFER_POOL_STATISTICS 01-FEB-23 YES
SYS WRH$_ROWCACHE_SUMMARY 01-FEB-23 YES
SYS WRH$_SGA 01-FEB-23 YES
SYS WRH$_SGASTAT 01-FEB-23 YES
SYS WRH$_PGASTAT 01-FEB-23 YES
SYS WRH$_PROCESS_MEMORY_SUMMARY 01-FEB-23 YES
SYS WRH$_RESOURCE_LIMIT 01-FEB-23 YES
SYS WRH$_SHARED_POOL_ADVICE 01-FEB-23 YES
SYS WRH$_SQL_WORKAREA_HISTOGRAM 01-FEB-23 YES
SYS WRH$_PGA_TARGET_ADVICE 01-FEB-23 YES
SYS WRH$_SGA_TARGET_ADVICE 01-FEB-23 YES
SYS WRH$_INSTANCE_RECOVERY 01-FEB-23 YES
SYS WRH$_RECOVERY_PROGRESS 29-JAN-23 YES
SYS WRH$_THREAD 01-FEB-23 YES
SYS WRH$_SYSSTAT 01-FEB-23 YES
SYS WRH$_CON_SYSSTAT 01-FEB-23 YES
SYS WRH$_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_CON_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_OSSTAT 01-FEB-23 YES
SYS WRH$_PARAMETER 01-FEB-23 YES
SYS WRH$_MVPARAMETER 01-FEB-23 YES
SYS WRH$_UNDOSTAT 01-FEB-23 YES
SYS WRH$_SEG_STAT 01-FEB-23 YES
SYS WRH$_SEG_STAT_OBJ 01-FEB-23 YES
SYS WRH$_SYSMETRIC_HISTORY 01-FEB-23 YES
SYS WRH$_SYSMETRIC_SUMMARY 01-FEB-23 YES
SYS WRH$_CON_SYSMETRIC_SUMMARY 01-FEB-23 YES
SYS WRH$_ACTIVE_SESSION_HISTORY 01-FEB-23 YES
SYS WRH$_TABLESPACE_STAT 01-FEB-23 YES
SYS WRH$_LOG 01-FEB-23 YES
SYS WRH$_TABLESPACE 31-JAN-23 YES
SYS WRH$_TABLESPACE_SPACE_USAGE 01-FEB-23 YES
SYS WRH$_SERVICE_NAME 01-FEB-23 YES
SYS WRH$_SERVICE_STAT 01-FEB-23 YES
SYS WRH$_SERVICE_WAIT_CLASS 01-FEB-23 YES
SYS WRI$_SCH_CONTROL 01-FEB-23 YES
SYS WRI$_SCH_VOTES 01-FEB-23 YES
SYS WRH$_RSRC_CONSUMER_GROUP 01-FEB-23 YES
SYS WRH$_RSRC_PLAN 01-FEB-23 YES
SYS WRH$_RSRC_METRIC 01-FEB-23 YES
SYS WRH$_RSRC_PDB_METRIC 01-FEB-23 YES
SYS WRH$_MEM_DYNAMIC_COMP 01-FEB-23 YES
SYS WRH$_DISPATCHER 01-FEB-23 YES
SYS WRH$_SHARED_SERVER_SUMMARY 01-FEB-23 YES
SYS WRM$_WR_USAGE 01-FEB-23 YES
SYS WRM$_DATABASE_INSTANCE 01-FEB-23 YES
SYS WRM$_SNAPSHOT 01-FEB-23 YES
SYS WRM$_SNAPSHOT_DETAILS 01-FEB-23 YES
SYS WRM$_SNAP_ERROR 01-FEB-23 YES
SYS WRM$_PDB_IN_SNAP 01-FEB-23 YES
SYS WRM$_WR_CONTROL 01-FEB-23 YES
SYS WRH$_PROCESS_WAITTIME 01-FEB-23 YES
SYS WRH$_SESS_NETWORK 29-JAN-23 YES
SYS WRI$_OPTSTAT_HISTHEAD_HISTORY 01-FEB-23 YES
SYS WRI$_OPTSTAT_HISTGRM_HISTORY 01-FEB-23 YES
SYS WRH$_CON_SYSSTAT 01-FEB-23 YES
SYS WRH$_CON_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_PROCESS_WAITTIME 01-FEB-23 YES
SYS WRH$_SESS_NETWORK 29-JAN-23 YES
SYS WRH$_SYSMETRIC_HISTORY 01-FEB-23 YES
SYS WRH$_TABLESPACE_STAT 01-FEB-23 YES
SYS WRH$_OSSTAT 01-FEB-23 YES
SYS WRH$_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRH$_SERVICE_WAIT_CLASS 01-FEB-23 YES
SYS WRH$_EVENT_HISTOGRAM 01-FEB-23 YES
SYS WRH$_MVPARAMETER 01-FEB-23 YES
SYS WRM$_PDB_IN_SNAP 01-FEB-23 YES
SYS WRH$_CON_SYS_TIME_MODEL 01-FEB-23 YES
SYS WRP$_REPORTS_TIME_BANDS 01-FEB-23 YES
SYS WRP$_REPORTS 01-FEB-23 YES
SYS WRP$_REPORTS_DETAILS 01-FEB-23 YES
SYS WRH$_SQLSTAT 01-FEB-23 YES
SYS WRH$_SYSTEM_EVENT 01-FEB-23 YES
SYS WRH$_WAITSTAT 01-FEB-23 YES
SYS WRH$_LATCH 01-FEB-23 YES
SYS WRH$_LATCH_MISSES_SUMMARY 01-FEB-23 YES
SYS WRH$_DB_CACHE_ADVICE 01-FEB-23 YES
SYS WRH$_ROWCACHE_SUMMARY 01-FEB-23 YES
SYS WRH$_SGASTAT 01-FEB-23 YES
SYS WRH$_SYSSTAT 01-FEB-23 YES
SYS WRH$_PARAMETER 01-FEB-23 YES
SYS WRH$_SEG_STAT 01-FEB-23 YES
SYS WRH$_SERVICE_STAT 01-FEB-23 YES
144 rows selected.
SQL> exec dbms_stats.gather_database_stats(cascade=>TRUE,method_opt =>'FOR ALL COLUMNS SIZE AUTO');
PL/SQL procedure successfully completed.
SQL>
----- For faster execution
SQL>
SQL>
SQL> EXEC DBMS_STATS.GATHER_DATABASE_STATS(ESTIMATE_PERCENT=>DBMS_STATS.AUTO_SAMPLE_SIZE,degree=>6);
PL/SQL procedure successfully completed.
SQL>
---or
SQL>
SQL> EXEC DBMS_STATS.GATHER_DATABASE_STATS(ESTIMATE_PERCENT=>DBMS_STATS.AUTO_SAMPLE_SIZE,degree=>6);
PL/SQL procedure successfully completed.
SQL> SCHEMA LEVEL
Gathering statistics for all objects in a schema, cascade will include indexes. If not used Oracle will determine whether to collect it or not.exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO; select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='&owner; set timing on exec dbms_stats.gather_schema_stats(ownname=>'&schema_name', CASCADE=>TRUE,ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4); OR exec dbms_stats.gather_schema_stats(ownname=>'&schema_name',ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4); -- CASCADE is not included here. Let Oracle will determine whether to collect statatics on indexes or not. OR EXEC DBMS_STATS.GATHER_SCHEMA_STATS ('&schema_name'); Will gather stats on 100% of schema tables.
[oracle@oracle-db-19c ~]$
[oracle@oracle-db-19c ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Thu Feb 2 10:17:57 2023
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> set pagesize 200
SQL> set linesize 200
SQL>
SQL> exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO;
PL/SQL procedure successfully completed.
SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='&owner';
Enter value for owner: sys
old 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='&owner'
new 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='sys'
no rows selected
SQL> select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='&owner';
Enter value for owner: SYS
old 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='&owner'
new 1: select OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS where STALE_STATS='YES' and OWNER='SYS'
OWNER
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
TABLE_NAME
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
LAST_ANALYZED STALE_STATS
--------------- ---------------------
SYS
WRP$_REPORTS
02-FEB-23 YES
SYS
WRP$_REPORTS_TIME_BANDS
02-FEB-23 YES
SYS
HIST_HEAD$
02-FEB-23 YES
SYS
TABPART$
02-FEB-23 YES
SYS
KU_UTLUSE
02-FEB-23 YES
SYS
WRM$_DATABASE_INSTANCE
02-FEB-23 YES
SYS
USTATS$
02-FEB-23 YES
SYS
OPTSTAT_HIST_CONTROL$
02-FEB-23 YES
SYS
SCHEDULER$_JOB
02-FEB-23 YES
SYS
COL_USAGE$
02-FEB-23 YES
SYS
CLU$
02-FEB-23 YES
SYS
WRP$_REPORTS_DETAILS
02-FEB-23 YES
SYS
TAB$
02-FEB-23 YES
SYS
HISTGRM$
02-FEB-23 YES
SYS
MON_MODS_ALL$
02-FEB-23 YES
SYS
INDPART$
02-FEB-23 YES
SYS
TABCOMPART$
02-FEB-23 YES
SYS
IND$
02-FEB-23 YES
SYS
WRM$_WR_CONTROL
02-FEB-23 YES
SYS
WRI$_SQLMON_USAGE
02-FEB-23 YES
SYS
WRP$_REPORTS
02-FEB-23 YES
SYS
WRP$_REPORTS_TIME_BANDS
02-FEB-23 YES
SYS
WRP$_REPORTS_DETAILS
02-FEB-23 YES
23 rows selected.
SQL> set timing on
SQL>
SQL> exec dbms_stats.gather_schema_stats(ownname=>'&schema_name',CASCADE=>TRUE,ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4);
Enter value for schema_name: hr
BEGIN dbms_stats.gather_schema_stats(ownname=>'hr',CASCADE=>TRUE,ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4); END;
*
ERROR at line 1:
ORA-20000: Schema "HR" does not exist or insufficient privileges
ORA-06512: at "SYS.DBMS_STATS", line 42210
ORA-06512: at "SYS.DBMS_STATS", line 42165
ORA-06512: at "SYS.DBMS_STATS", line 9404
ORA-06512: at "SYS.DBMS_STATS", line 42048
ORA-06512: at "SYS.DBMS_STATS", line 42196
ORA-06512: at line 1
Elapsed: 00:00:00.02
SQL> exec dbms_stats.gather_schema_stats(ownname=>'&schema_name',CASCADE=>TRUE,ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4);
Enter value for schema_name: SYS
PL/SQL procedure successfully completed.
Elapsed: 00:00:55.78
SQL>
SQL>
SQL>
SQL> exec dbms_stats.gather_schema_stats(ownname=>'&schema_name',ESTIMATE_PERCENT=>dbms_stats.auto_sample_size,degree =>4);
Enter value for schema_name: SYS
PL/SQL procedure successfully completed.
Elapsed: 00:01:03.20
SQL>
SQL>
SQL>
SQL> EXEC DBMS_STATS.GATHER_SCHEMA_STATS ('&schema_name');
Enter value for schema_name: SYS
PL/SQL procedure successfully completed.
Elapsed: 00:00:58.80
SQL> TABLE Level
-- The CASCADE parameter determines whether or not statistics are gathered for the indexes on a table. exec DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO; SELECT OWNER,TABLE_NAME,LAST_ANALYZED,STALE_STATS from DBA_TAB_STATISTICS WHERE TABLE_NAME='&TNAME'; exec dbms_stats.gather_table_stats(ownname=>'&Schema_name',tabname=>'&Table_name',estimate_percent=>DBMS_STATS.AUTO_SAMPLE_SIZE,cascade=>TRUE,degree =>4); OR -- Gather statistics on the table with histograms being automatically created exec dbms_stats.gather_table_stats('&SCHEMA_NAME','&Table_name');
Index Statistics
exec DBMS_STATS.GATHER_INDEX_STATS(ownname => '&OWNER',indname =>'&INDEX_NAME',estimate_percent =>DBMS_STATS.AUTO_SAMPLE_SIZE);SYSTEM STATISTICS
What is system statistics?
System statistics are statistics about CPU speed and IO performance, it enables the CBO to effectively cost each operation in an execution plan. Introduced in Oracle 9i.
Why gathering system statistics?
Oracle highly recommends gathering system statistics during a representative workload, ideally at peak workload time, in order to provide more accurate CPU/IO cost estimates to the optimizer. You only have to gather system statistics once.
There are two types of system statistics (NOWORKLOAD statistics & WORKLOAD statistics):
NOWORKLOAD statistics:
This will simulates a workload -not the real one but a simulation- and will not collect full statistics, it's less accurate than "WORKLOAD statistics" but if you can't capture the statistics during a typical workload you can use noworkload statistics. To gather noworkload statistics:
SQL> execute dbms_stats.gather_system_stats();
SQL>
SQL>
SQL> execute dbms_stats.gather_system_stats();
PL/SQL procedure successfully completed.
Elapsed: 00:00:25.33
SQL> WORKLOAD statistics:
This will gather statistics during the current workload [which supposed to be representative of actual system I/O and CPU workload on the DB]. To gather WORKLOAD statistics:
SQL>
SQL> execute dbms_stats.gather_system_stats('start');
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.06
SQL> Once the workload window ends after 1,2,3.. hours or whatever, stop the system statistics gathering:
SQL> execute dbms_stats.gather_system_stats('stop');
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.14
SQL> You can use time interval (minutes) instead of issuing start/stop command manually:
SQL> execute dbms_stats.gather_system_stats('interval',60);
Check the system values collected:
SQL>
SQL> show user;
USER is "SYS"
SQL> col pname format a20
SQL> col pval2 format a40
SQL> select * from sys.aux_stats$;
SNAME PNAME PVAL1 PVAL2
------------------------------------------------------------------------------------------ -------------------- ---------- ----------------------------------------
SYSSTATS_INFO STATUS COMPLETED
SYSSTATS_INFO DSTART 02-02-2023 10:49
SYSSTATS_INFO DSTOP 02-02-2023 10:50
SYSSTATS_INFO FLAGS 1
SYSSTATS_MAIN CPUSPEEDNW 2943
SYSSTATS_MAIN IOSEEKTIM 16
SYSSTATS_MAIN IOTFRSPEED 4096
SYSSTATS_MAIN SREADTIM .008
SYSSTATS_MAIN MREADTIM
SYSSTATS_MAIN CPUSPEED 2944
SYSSTATS_MAIN MBRC
SYSSTATS_MAIN MAXTHR
SYSSTATS_MAIN SLAVETHR
13 rows selected.
Elapsed: 00:00:00.16
SQL> cpuspeedNW: Shows the noworkload CPU speed, (average number of CPU cycles per second). ioseektim: The sum of seek time, latency time, and OS overhead time. iotfrspeed: I/O transfer speed,tells optimizer how fast the DB can read data in a single read request. cpuspeed: Stands for CPU speed during a workload statistics collection. maxthr: The maximum I/O throughput. slavethr: Average parallel slave I/O throughput. sreadtim: The Single Block Read Time statistic shows the average time for a random single block read. mreadtim: The average time (seconds) for a sequential multiblock read. mbrc: The average multiblock read count in blocks. Notes: -When gathering NOWORKLOAD statistics it will gather (cpuspeedNW, ioseektim, iotfrspeed) system statistics only. -Above values can be modified manually using DBMS_STATS.SET_SYSTEM_STATS procedure. -According to Oracle, collecting workload statistics doesn't impose an additional overhead on your system.
Delete system statistics
SQL>
SQL>
SQL> execute dbms_stats.delete_system_stats();
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.00
SQL> How lock/unlock statistics on table
1.Create table and verify
SQL> create table raj ( x number );
Table created.
SQL> SELECT stattype_locked FROM dba_tab_statistics WHERE table_name='RAJ' and owner='SH';
STATT
-----
<---- Output NULL. Hence table unlocked. It will allow to gather stats on this table
SQL>2.Lock stats
SQL> exec dbms_stats.lock_table_stats('SH', 'RAJ');
PL/SQL procedure successfully completed.
SQL> 3. Verify
SQL> SELECT stattype_locked FROM dba_tab_statistics WHERE table_name='RAJ' and owner='SH';
STATT
-----
ALL <---- Hence table locked. It will not allow to gather stats on this table
SQL>
Tryied to gather stats, but fails
SQL> exec dbms_stats.gather_table_stats('sh', 'raj');
BEGIN dbms_stats.gather_table_stats('sh', 'raj'); END;
*
ERROR at line 1:
ORA-20005: object statistics are locked (stattype = ALL) <-- LOCKED4. Unlock
SQL> exec dbms_stats.unlock_table_stats('SH', 'RAJ');
PL/SQL procedure successfully completed.
SQL> SELECT stattype_locked FROM dba_tab_statistics WHERE table_name='RAJ' and owner='SH';
STATT
-----
<----it's unlocked, It will allow to gather stats on this table
SQL> exec dbms_stats.gather_table_stats('sh', 'raj');
PL/SQL procedure successfully completed.
SQL>
Locked: ALL
Unlocked: NULL