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Valeriu PLESNILA
2026-03-12 22:01:38 +01:00
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259
statistics/ex_when_cbo_use_global_stats_on_part_table_01.txt Normal file
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-- https://franckpachot.medium.com/oracle-global-vs-partition-level-statistics-cbo-usage-1c2aa2aa3f32
create table DEMO (day date) partition by range(day) (
partition P2018 values less than (date '2019-01-01'),
partition P2019 values less than (date '2020-01-01'),
partition P2020 values less than (date '2021-01-01'),
partition P2021 values less than (date '2022-01-01'),
partition INFINIT values less than (MAXVALUE)
);
insert into DEMO
select date '2019-01-01'+rownum from xmltable('1 to 100');
insert into DEMO
select date '2018-01-01'-rownum/24 from xmltable('1 to 5000');
commit;
exec dbms_stats.gather_table_stats(user,'DEMO');
set lines 256
col OWNER for a20
col TABLE_NAME for a20
col PARTITION_NAME for a20
col LAST_ANALYZED for a20
col GLOBAL_STATS for a3
col STALE_STATS for a5
select OWNER,TABLE_NAME,PARTITION_NAME,NUM_ROWS,LAST_ANALYZED,GLOBAL_STATS,STALE_STATS from dba_tab_statistics where table_name='DEMO';
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO 5100 20-JAN-24 YES NO
POC DEMO P2020 0 20-JAN-24 YES NO
POC DEMO INFINIT 0 20-JAN-24 YES NO
POC DEMO P2018 5000 20-JAN-24 YES NO
POC DEMO P2019 100 20-JAN-24 YES NO
POC DEMO P2021 0 20-JAN-24 YES NO
Pstart = Pstop (PARTITION RANGE SINGLE) -> partition stats are used
--------------
select count(*) from DEMO where day between to_date( '2019-01-08','yyyy-mm-dd' ) and to_date( '2019-02-08','yyyy-mm-dd' ) ;
COUNT(*)
----------
32
----------------------------------------------------------------
| Id | Operation | Name | Rows | Pstart| Pstop |
----------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | PARTITION RANGE SINGLE| | 33 | 2 | 2 |
| 3 | TABLE ACCESS FULL | DEMO | 33 | 2 | 2 |
----------------------------------------------------------------
Partition-level statistics are used when only one partition is accessed, known at the time of parsing.
You see that with Pstart=Pstop = number.
Pstart <> Pstop (PARTITION RANGE ITERATOR/FULL) -> global stats are used
---------------
select count(*) from DEMO where day between to_date( '2019-01-08','yyyy-mm-dd' ) and to_date( '2019-02-08','yyyy-mm-dd' ) ;
COUNT(*)
----------
94
select * from dbms_xplan.display_cursor(format=>'basic +rows +outline +peeked_binds +partition');
------------------------------------------------------------------
| Id | Operation | Name | Rows | Pstart| Pstop |
------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | PARTITION RANGE ITERATOR| | 705 | 2 | 3 |
| 3 | TABLE ACCESS FULL | DEMO | 705 | 2 | 3 |
------------------------------------------------------------------
Note that nomber of rows is overestimated.
Global table level statistics are used when more than one partition is accessed, even when they are known at the time of parsing.
You see that with Pstart <> Pstop.
KEY — KEY (PARTITION RANGE ITERATOR/FULL) -> partition stats are used
----------
var d1 varchar2(10)
var d2 varchar2(10)
exec :d1:='2019-01-08';
exec :d2:='2019-02-08';
select count(*) from DEMO where day between to_date(:d1,'yyyy-mm-dd' ) and to_date(:d2,'yyyy-mm-dd' );
COUNT(*)
----------
32
-------------------------------------------------------------------
| Id | Operation | Name | Rows | Pstart| Pstop |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | FILTER | | | | |
| 3 | PARTITION RANGE ITERATOR| | 33 | KEY | KEY |
| 4 | TABLE ACCESS FULL | DEMO | 33 | KEY | KEY |
-------------------------------------------------------------------
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('19.1.0')
DB_VERSION('19.1.0')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
FULL(@"SEL$1" "DEMO"@"SEL$1")
END_OUTLINE_DATA
*/
Peeked Binds (identified by position):
--------------------------------------
1 - :D1 (VARCHAR2(30), CSID=873): '2019-01-08'
2 - :D2 (VARCHAR2(30), CSID=873): '2019-02-08'
Partition-level statistics are used when only one partition is accessed, known at the time of parsing, even the value is known with bind peeking.
You see that with KEY/KEY for Pstart/Pstop and with bind variables listed by +peeked_binds format
Without bind peeking -> global
--------------------
Same previous binded query but with the bind peeking disabled at the session level.
alter system flush shared_pool;
select count(*) from DEMO where day between to_date(:d1,'yyyy-mm-dd' ) and to_date(:d2,'yyyy-mm-dd' );
COUNT(*)
----------
32
select * from dbms_xplan.display_cursor(format=>'basic +rows +outline +peeked_binds +partition');
-------------------------------------------------------------------
| Id | Operation | Name | Rows | Pstart| Pstop |
-------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | |
| 1 | SORT AGGREGATE | | 1 | | |
| 2 | FILTER | | | | |
| 3 | PARTITION RANGE ITERATOR| | 13 | KEY | KEY |
| 4 | TABLE ACCESS FULL | DEMO | 13 | KEY | KEY |
-------------------------------------------------------------------
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('19.1.0')
DB_VERSION('19.1.0')
OPT_PARAM('_optim_peek_user_binds' 'false')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
FULL(@"SEL$1" "DEMO"@"SEL$1")
END_OUTLINE_DATA
*/
The number of rows is underestimated, global stats has been used.
In conclusion, there is only one case where the partition level statistics can be used:
partition pruning to one single partition, at parse time by the literal value or the peeked bind.
--------------------------------------
Extra (example online split partition)
--------------------------------------
-- add the next 5000 days since 1 Jan 2022
insert into DEMO
select date '2022-01-01'+rownum from xmltable('1 to 5000');
commit;
-- create P2022, P2022 and P2023 partitions using split online
ALTER TABLE DEMO
SPLIT PARTITION INFINIT AT (date '2023-01-01')
INTO (PARTITION P2022,
PARTITION INFINIT)
ONLINE;
ALTER TABLE DEMO
SPLIT PARTITION INFINIT AT (date '2024-01-01')
INTO (PARTITION P2023,
PARTITION INFINIT)
ONLINE;
ALTER TABLE DEMO
SPLIT PARTITION INFINIT AT (date '2025-01-01')
INTO (PARTITION P2024,
PARTITION INFINIT)
ONLINE;
exec dbms_stats.gather_table_stats(user,'DEMO');
col OWNER for a20
col TABLE_NAME for a20
col PARTITION_NAME for a20
col LAST_ANALYZED for a20
col GLOBAL_STATS for a3
col STALE_STATS for a5
select OWNER,TABLE_NAME,PARTITION_NAME,NUM_ROWS,LAST_ANALYZED,GLOBAL_STATS,STALE_STATS from dba_tab_statistics where table_name='DEMO';
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO 10100 20-JAN-24 YES NO
POC DEMO P2020 0 20-JAN-24 YES NO
POC DEMO P2022 364 20-JAN-24 YES NO
POC DEMO INFINIT 3905 20-JAN-24 YES NO
POC DEMO P2018 5000 20-JAN-24 YES NO
POC DEMO P2019 100 20-JAN-24 YES NO
POC DEMO P2021 0 20-JAN-24 YES NO
POC DEMO P2024 366 20-JAN-24 YES NO
POC DEMO P2023 365 20-JAN-24 YES NO
-- check boundaries
select min(day),max(day) from DEMO partition (P2022);
MIN(DAY) MAX(DAY)
--------- ---------
02-JAN-22 31-DEC-22
select min(day),max(day) from DEMO partition (P2023);
MIN(DAY) MAX(DAY)
--------- ---------
01-JAN-23 31-DEC-23
select min(day),max(day) from DEMO partition (P2024);
MIN(DAY) MAX(DAY)
--------- ---------
01-JAN-24 31-DEC-24

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statistics/example_incremental_stats__01 Normal file
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create table DEMO (day date) partition by range(day) (
partition P2000 values less than (date '2001-01-01'),
partition P2001 values less than (date '2002-01-01'),
partition P2002 values less than (date '2003-01-01'),
partition P2003 values less than (date '2004-01-01'),
partition P2004 values less than (date '2005-01-01'),
partition P2005 values less than (date '2006-01-01'),
partition INFINITY values less than (MAXVALUE)
);
-- by default GRANULARITY=AUTO and INCREMENTAL=FALSE
-- on this table overwrite property GRANULARITY
exec DBMS_STATS.SET_TABLE_PREFS(ownname=>'POC',tabname=>'DEMO', pname=>'GRANULARITY', pvalue=>'PARTITION');
-- insert some lines in the first 4 partitions
insert into DEMO select date '2000-01-01'+rownum from xmltable('1 to 1460');
commit;
-- gather stats on the first 5 partitions
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2000');
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2001');
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2002');
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2003');
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2004');
-- show table stats
set lines 256
col OWNER for a20
col TABLE_NAME for a20
col PARTITION_NAME for a20
col LAST_ANALYZED for a20
col GLOBAL_STATS for a3
col STALE_STATS for a5
select OWNER,TABLE_NAME,PARTITION_NAME,NUM_ROWS,LAST_ANALYZED,GLOBAL_STATS,STALE_STATS from dba_tab_statistics where table_name='DEMO' order by PARTITION_POSITION asc;
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO P2000 365 21-JAN-24 YES NO
POC DEMO P2001 365 21-JAN-24 YES NO
POC DEMO P2002 365 21-JAN-24 YES NO
POC DEMO P2003 365 21-JAN-24 YES NO
POC DEMO P2004 0 21-JAN-24 YES NO
POC DEMO P2005 NO
POC DEMO INFINITY NO
POC DEMO NO
-- as expected, 365 lines in the first 4 partitions, 0 lines in ther 5-th partition and no stats on other partitions
-- also, no global stats at table level
-- now set INCREMENTAL property to TRUE for the table
exec DBMS_STATS.SET_TABLE_PREFS(ownname=>'POC',tabname=>'DEMO', pname=>'INCREMENTAL', pvalue=>'TRUE');
-- get statistics on P2005
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'P2005');
-- still no global stats, because no stats last partition
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO P2000 365 21-JAN-24 YES NO
POC DEMO P2001 365 21-JAN-24 YES NO
POC DEMO P2002 365 21-JAN-24 YES NO
POC DEMO P2003 365 21-JAN-24 YES NO
POC DEMO P2004 0 21-JAN-24 YES NO
POC DEMO P2005 0 21-JAN-24 YES NO
POC DEMO INFINITY NO
POC DEMO NO
-- get statistics on the last partition
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DEMO',partname=>'INFINITY');
-- now we can see global stats at the table level
-- note that GLOBAL_STATS=NO and STALE_STATS=YES for the global (aggregate) table stats
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO P2000 365 21-JAN-24 YES NO
POC DEMO P2001 365 21-JAN-24 YES NO
POC DEMO P2002 365 21-JAN-24 YES NO
POC DEMO P2003 365 21-JAN-24 YES NO
POC DEMO P2004 0 21-JAN-24 YES NO
POC DEMO P2005 0 21-JAN-24 YES NO
POC DEMO INFINITY 0 21-JAN-24 YES NO
POC DEMO 1460 21-JAN-24 NO YES
-- now delete table stats and use gather_table_stats to gather stats on the whole table
exec dbms_stats.delete_table_stats(user,'DEMO');
exec dbms_stats.gather_table_stats(user,'DEMO');
-- the result is identical as getting stats individually for each partition
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO P2000 365 21-JAN-24 YES NO
POC DEMO P2001 365 21-JAN-24 YES NO
POC DEMO P2002 365 21-JAN-24 YES NO
POC DEMO P2003 365 21-JAN-24 YES NO
POC DEMO P2004 0 21-JAN-24 YES NO
POC DEMO P2005 0 21-JAN-24 YES NO
POC DEMO INFINITY 0 21-JAN-24 YES NO
POC DEMO 1460 21-JAN-24 NO YES
-- reset table prefs to default values
exec DBMS_STATS.SET_TABLE_PREFS(ownname=>'POC',tabname=>'DEMO', pname=>'GRANULARITY', pvalue=>'AUTO');
exec DBMS_STATS.SET_TABLE_PREFS(ownname=>'POC',tabname=>'DEMO', pname=>'INCREMENTAL', pvalue=>'FALSE');
-- delete and gather table stats
exec dbms_stats.delete_table_stats(user,'DEMO');
exec dbms_stats.gather_table_stats(user,'DEMO');
-- note that GLOBAL_STATS=YES and STALE_STATS=NO for the global (aggregate) table stats
OWNER TABLE_NAME PARTITION_NAME NUM_ROWS LAST_ANALYZED GLO STALE
-------------------- -------------------- -------------------- ---------- -------------------- --- -----
POC DEMO P2000 365 21-JAN-24 YES NO
POC DEMO P2001 365 21-JAN-24 YES NO
POC DEMO P2002 365 21-JAN-24 YES NO
POC DEMO P2003 365 21-JAN-24 YES NO
POC DEMO P2004 0 21-JAN-24 YES NO
POC DEMO P2005 0 21-JAN-24 YES NO
POC DEMO INFINITY 0 21-JAN-24 YES NO
POC DEMO 1460 21-JAN-24 YES NO
-- CONCLUSION: when INCREMENTAL stats are activated:
- ALL partitions stats are required in order to estimate the GLOBAL table stats
- in DBA_TAB_STATISTICS, columns GLOBAL_STATS=NO and STALE_STATS=YES for the aggregated table stats

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statistics/stats_getpref_global.sql Executable file
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SET SERVEROUTPUT ON
DECLARE
PROCEDURE display(p_param IN VARCHAR2) AS
l_result VARCHAR2(50);
BEGIN
l_result := DBMS_STATS.get_prefs (pname => p_param);
DBMS_OUTPUT.put_line(RPAD(p_param, 30, ' ') || ' : ' || l_result);
END;
BEGIN
display('APPROXIMATE_NDV_ALGORITHM');
display('AUTO_STAT_EXTENSIONS');
display('AUTO_TASK_STATUS');
display('AUTO_TASK_MAX_RUN_TIME');
display('AUTO_TASK_INTERVAL');
display('CASCADE');
display('CONCURRENT');
display('DEGREE');
display('ESTIMATE_PERCENT');
display('GLOBAL_TEMP_TABLE_STATS');
display('GRANULARITY');
display('INCREMENTAL');
display('INCREMENTAL_STALENESS');
display('INCREMENTAL_LEVEL');
display('METHOD_OPT');
display('NO_INVALIDATE');
display('OPTIONS');
display('PREFERENCE_OVERRIDES_PARAMETER');
display('PUBLISH');
display('STALE_PERCENT');
display('STAT_CATEGORY');
display('TABLE_CACHED_BLOCKS');
display('STALE_PERCENT');
display('WAIT_TIME_TO_UPDATE_STATS');
END;
/

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statistics/stats_getpref_table.sql Executable file
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SET SERVEROUTPUT ON
DECLARE
PROCEDURE display(p_param IN VARCHAR2) AS
l_result VARCHAR2(50);
BEGIN
l_result := DBMS_STATS.get_prefs (pname=>p_param,ownname=>'&1',tabname=>'&2');
DBMS_OUTPUT.put_line(RPAD(p_param, 30, ' ') || ' : ' || l_result);
END;
BEGIN
display('APPROXIMATE_NDV_ALGORITHM');
display('AUTO_STAT_EXTENSIONS');
display('AUTO_TASK_STATUS');
display('AUTO_TASK_MAX_RUN_TIME');
display('AUTO_TASK_INTERVAL');
display('CASCADE');
display('CONCURRENT');
display('DEGREE');
display('ESTIMATE_PERCENT');
display('GLOBAL_TEMP_TABLE_STATS');
display('GRANULARITY');
display('INCREMENTAL');
display('INCREMENTAL_STALENESS');
display('INCREMENTAL_LEVEL');
display('METHOD_OPT');
display('NO_INVALIDATE');
display('OPTIONS');
display('PREFERENCE_OVERRIDES_PARAMETER');
display('PUBLISH');
display('STALE_PERCENT');
display('STAT_CATEGORY');
display('TABLE_CACHED_BLOCKS');
display('STALE_PERCENT');
display('WAIT_TIME_TO_UPDATE_STATS');
END;
/