Statistics played in key role in Oracle performance tuning. Oracle Optimizer creates the execution plan based on the statistics of the Oracle table involved in the SQL queries.
You may want to lock statistics in an Oracle table in some cases, for example
- you don’t want a table to be analyzed by a scheduled statistics job but want to analyze it later or at a higher estimate
- you don’t want to generate the statistics for the table for performance reason
- you don’t want the server to spend time generating statistics when the table data doesn’t change
There could be many more cases where we want to lock statistics
How to lock statistics on the table
You can use the standard Oracle package DBMS_STATS to lock the statistics on the table
exec dbms_stats.lock_table_stats('table_owner','table_name');
Example
SELECT stattype_locked FROM dba_tab_statistics WHERE table_name = 'TEST' and owner = 'TECH';
STATTYPE_LOCKED
—–------------
exec dbms_stats.lock_table_stats('TEST','TECH');
SELECT stattype_locked FROM dba_tab_statistics WHERE table_name = 'TEST' and owner = 'TECH';
STATTYPE_LOCKED
—–--------
ALL
How to lock statistics on the schema
You can use the standard Oracle package DBMS_STATS to lock the statistics on the schema
exec dbms_stats.lock_schema_stats('<schema name>');
How to lock statistics on the table partition
exec dbms_stats.lock_partition_stats('<table_owner>', '<table_name>', '<partition_name>');
How to find the table where statistics are locked in Oracle
You can use the below query to find all the tables where statistics is locked
select owner, table_name, stattype_locked from dba_tab_statistics where stattype_locked is not null;
Running stats generation Job on the table where statistics is locked
If we try to run gather statistics on the tables where statistics is locked, we get ORA-20005 object statistics are locked (stattype = all)
SQL> exec dbms_stats.gather_table_stats('TECH', 'TEST');
BEGIN dbms_stats.gather_table_stats('TECH', 'TEST'); END;
*
ERROR at line 1:
ORA-20005: object statistics are locked (stattype = ALL)
ORA-06512: at “SYS.DBMS_STATS”, line 10640
ORA-06512: at “SYS.DBMS_STATS”, line 10664
ORA-06512: at line 1
We can perform the below steps to unlock the statistics, generate the statistics and lock them again
exec dbms_stats.unlock_table_stats('TECH','TEST');
exec dbms_stats.gather_table_stats('TECH', 'TEST');
exec dbms_stats.lock_table_stats('TECH','TEST');
or
exec dbms_stats.gather_table_stats('TECH', 'TEST',force=>true);
How to unlock statistics for Table and schema /unlock table stats for schema
Now once we find the objects, we can use the below queries to unlock them
unlock schema stats
exec dbms_stats.unlock_schema_stats('schema_owner');
Unlock table stats
exec dbms_stats.unlock_table_stats('table_owner','table_name');
Unlock table partition stats
exec dbms_stats.unlock_partition_stats('table_owner','table_name','partition name');
Example
exec dbms_stats.unlock_schema_stats('TECH');
exec dbms_stats.unlock_table_stats('TECH','TEST');
Index creation with statistics locked on the table
10g onwards, whenever we create an index, the statistics are generated automatically. Now this equation changes When the table is locked, statistics will not be generated while creating the index. We need to use the FORCE option to gather the statistics while creating an index for locked objects.Let’s understand that in detail by seeing the example
Example Lets first create the dummy table and lock the statistics on that table SQL> create table test as select a.* ,rownum id from all_objects a where rownum <1001; SQL> exec dbms_stats.lock_table_stats('TECH','TEST'); Now we will try to create index SQL> create index test_idx on test(id); Index created. SQL> select num_rows, last_analyzed from user_ind_statistics where index_name ='TEST_IDX'; NUM_ROWS LAST_ANAL ---------- --------- So statistics on index is not generated automatically for the locked statistics table Lets try to generate the statistics using DBMS_STATS SQL> exec dbms_stats.gather_index_stats(null, 'TEST_IDX'); BEGIN dbms_stats.gather_index_stats(null, 'TEST_IDX'); END; * ERROR at line 1: ORA-20005: object statistics are locked (stattype = ALL) ORA-06512: at "SYS.DBMS_STATS", line 10640 ORA-06512: at "SYS.DBMS_STATS", line 10664 ORA-06512: at line 1 So statistics generation failed. In order to generate stats on the index, We can use force option in dbms_stats to override this SQL> exec dbms_stats.gather_index_stats(null, 'TEST_IDX',force=>true); PL/SQL procedure successfully completed. SQL> select num_rows, last_analyzed from user_ind_statistics where index_name ='IDX'; NUM_ROWS LAST_ANAL ---------- --------- 1000 01-SEP-17 Lets try to create a new index with compute statistics clause SQL> create index TEST_IDX1 on test(object_name) compute statistics; create index idx on test(object_name) compute statistics * ERROR at line 1: ORA-38029: object statistics are locked So ORA-38029 error happens, So we need to create index with out the compute statistics clause and then generate stats using force option SQL> create index TEST_IDX1 on test(object_name); SQL> exec dbms_stats.gather_index_stats(null, 'TEST_IDX1',force=>true); Same things happens if we rebuild the index with compute statistics option SQL> alter index TEST_IDX1 rebuild compute statistics; alter index TEST_IDX1 rebuild compute statistics * ERROR at line 1: ORA-38029: object statistics are locked SQL> alter index TEST_IDX1 rebuild; Index altered. SQL> exec dbms_stats.gather_index_stats(null, 'TEST_IDX1',force=>true); PL/SQL procedure successfully completed.
Hope you like the information on how to lock/unlock table statistics in Oracle,How to find table where statistics are locked. Also Now you must know what to do when ORA-20005: object statistics are locked and ORA-38029: object statistics are locked happens
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