Goal :
The goal is to explain why the view DBA_TAB_MODIFICATIONS does sometimes have no values
even when the parameter STATISTICS_LEVEL is set to TYPICAL and the specific schema has been analyzed successful using the package DBMS_STATS.GATHER_SCHEMA_STATS.
In addition all the tables in that schema shows MONITORING=YES in the view dba_tables.
Fix:
The updates to the table *_tab_modifications are related to the volumne of updates for a table.
There is a need of approximately 10% of datavolumn changes. Just only on single update of the row for example might not lead to fill the *_tab_modifications.
Example :
SQL> create table test ( num varchar2(32));
Table created.
Lets insert 100 rows to table test:
SQL> begin
2 for i in 1..100 loop
3 insert into sys.test values (i);
4 end loop;
5 commit;
end; 6
7 /
PL/SQL procedure successfully completed.
SQL> select count(*) from test;
COUNT(*)
----------
100
Gather stats for this table:
SQL> EXEC DBMS_STATS.GATHER_TABLE_STATS('SYS','TEST');
PL/SQL procedure successfully completed.
SQL> SELECT OWNER,TABLE_NAME,STALE_STATS,NUM_ROWS,BLOCKS,EMPTY_BLOCKS FROM DBA_TAB_STATISTICS where OWNER ='SYS' AND TABLE_NAME='TEST';
OWNER TABLE_NAME STA NUM_ROWS
------------------------------ ------------------------------ --- ----------
BLOCKS EMPTY_BLOCKS
---------- ------------
SYS TEST NO 100
1 0
SQL> select * from dba_tab_modifications where TABLE_OWNER='SYS' AND TABLE_NAME='TEST';
no rows selected
Now lets manually flush the modifications from SGA:
Note: The procedure DBMS_STATS.FLUSH_DATABASE_MONITORING_INFO flushes in-memory monitoring information for all tables in the dictionary.
Corresponding entries in the *_TAB_MODIFICATIONS, *_TAB_STATISTICS and *_IND_STATISTICS views are updated immediately, without waiting for the Oracle database to flush them periodically (per default every 3 hours). This procedure is useful when you need up-to-date information in those views.
SQL> exec dbms_stats.flush_database_monitoring_info;
PL/SQL procedure successfully completed.
SQL> SELECT OWNER,TABLE_NAME,STALE_STATS,NUM_ROWS,BLOCKS,EMPTY_BLOCKS FROM DBA_TAB_STATISTICS where OWNER ='SYS' AND TABLE_NAME='TEST';
OWNER TABLE_NAME STA NUM_ROWS
------------------------------ ------------------------------ --- ----------
BLOCKS EMPTY_BLOCKS
---------- ------------
SYS TEST NO 100
1 0
Now lets insert 1000 more values and check if it put entry in dba_tab_modifications:
SQL> begin
for i in 1..1000 loop
insert into sys.test values (i);
end loop;
commit;
end;
/
2 3 4 5 6 7
PL/SQL procedure successfully completed.
SQL> select count(*) from test;
COUNT(*)
----------
1100
SQL> SELECT OWNER,TABLE_NAME,STALE_STATS,NUM_ROWS,BLOCKS,EMPTY_BLOCKS FROM DBA_TAB_STATISTICS where OWNER ='SYS' AND TABLE_NAME='TEST';
OWNER TABLE_NAME STA NUM_ROWS
------------------------------ ------------------------------ --- ----------
BLOCKS EMPTY_BLOCKS
---------- ------------
SYS TEST NO 100
1 0
no rows selected
SQL> select * from dba_tab_modifications where TABLE_OWNER='SYS' AND TABLE_NAME='TEST';
no rows selected
SQL> SELECT OWNER,TABLE_NAME,STALE_STATS,NUM_ROWS,BLOCKS,EMPTY_BLOCKS FROM DBA_TAB_STATISTICS where OWNER ='SYS' AND TABLE_NAME='TEST';
OWNER TABLE_NAME STA NUM_ROWS
------------------------------ ------------------------------ --- ----------
BLOCKS EMPTY_BLOCKS
---------- ------------
SYS TEST NO 100
1 0
SQL> exec dbms_stats.flush_database_monitoring_info;
PL/SQL procedure successfully completed.
SQL> SELECT OWNER,TABLE_NAME,STALE_STATS,NUM_ROWS,BLOCKS,EMPTY_BLOCKS FROM DBA_TAB_STATISTICS where OWNER ='SYS' AND TABLE_NAME='TEST';
OWNER TABLE_NAME STA NUM_ROWS
------------------------------ ------------------------------ --- ----------
BLOCKS EMPTY_BLOCKS
---------- ------------
SYS TEST YES 100
1 0
SQL> select * from dba_tab_modifications where TABLE_OWNER='SYS' AND TABLE_NAME='TEST';
TABLE_OWNER TABLE_NAME
------------------------------ ------------------------------
PARTITION_NAME SUBPARTITION_NAME INSERTS
------------------------------ ------------------------------ ----------
UPDATES DELETES TIMESTAMP TRU DROP_SEGMENTS
---------- ---------- --------- --- -------------
SYS TEST
1000
0 0 19-JUN-12 NO 0
