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在12C RAC的in memory测试中由于未正确启用并行,导致测试结果flush buffer cache后,总是出现大量并行，通过ORACLE 各方努力最终确定是由于parallel_degree_policy=AUTO和parallel_force_local=false开始未设置正确导致.在rac中需要imdb的朋友请注意这两个参数.
设置表存放中inmemory
SQL> alter table CHF.XIFENFEI_888 inmemory;
Table altered.
SQL> set autot on
SQL> select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 2566 (8)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 2566 (8)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 2566 (8)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
213 recursive calls
0 db block gets
435058 consistent gets
40 physical reads
61180 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
5 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> set autot off
SQL> select * from gv$im_segments where owner='CHF' and segment_name='XIFENFEI_888'
no rows selected
SQL> select * from gv$im_segments where owner='CHF' and segment_name='XIFENFEI_888'
INST_ID OWNER SEGMENT_NAME PARTI SEGME TABLESPACE_NAME INMEMORY_SIZE BYTES BYTES_NOT_POPULATED POPULATE_ INMEMORY INMEMORY_DISTRI INMEMORY_DUPL INMEMORY_COMPRESS CON_ID
------- ----- --------------- ----- ----- --------------- ------------- ------------ ------------------- --------- -------- --------------- ------------- ----------------- ------
1 CHF XIFENFEI_888 TABLE CHF_DATA 469827584 3571449856 2853101568 STARTED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
2 CHF XIFENFEI_888 TABLE CHF_DATA 332267520 3571449856 3040182272 STARTED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
SQL> select * from gv$im_segments where owner='CHF' and segment_name='XIFENFEI_888'
INST_ID OWNER SEGMENT_NAME PARTI SEGME TABLESPACE_NAME INMEMORY_SIZE BYTES BYTES_NOT_POPULATED POPULATE_ INMEMORY INMEMORY_DISTRI INMEMORY_DUPL INMEMORY_COMPRESS CON_ID
------- ----- --------------- ----- ----- --------------- ------------- ------------ ------------------- --------- -------- --------------- ------------- ----------------- ------
1 CHF XIFENFEI_888 TABLE CHF_DATA 1510211584 3571449856 1444610048 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
2 CHF XIFENFEI_888 TABLE CHF_DATA 1068433408 3571449856 2058321920 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
这里可以看到表加载到inmemory需要时间,不是全表扫描一遍之后里面全表载入到in memory中.
查看执行计划确实走inmemory
SQL> set autot on
SQL> select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18629 (1)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
6 recursive calls
0 db block gets
177415 consistent gets
0 physical reads
23484 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
flush buffer cache后,inmemory执行计划中出现大量物理读
SQL> set autot off
SQL> alter system flush buffer_cache;
System altered.
SQL> /
System altered.
SQL> select * from gv$im_segments where owner='CHF' and segment_name='XIFENFEI_888'
INST_ID OWNER SEGMENT_NAME PARTI SEGME TABLESPACE_NAME INMEMORY_SIZE BYTES BYTES_NOT_POPULATED POPULATE_ INMEMORY INMEMORY_DISTRI INMEMORY_DUPL INMEMORY_COMPRESS CON_ID
------- ----- --------------- ----- ----- --------------- ------------- ------------ ------------------- --------- -------- --------------- ------------- ----------------- ------
1 CHF XIFENFEI_888 TABLE CHF_DATA 1510211584 3571449856 1444610048 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
2 CHF XIFENFEI_888 TABLE CHF_DATA 1068433408 3571449856 2058321920 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
SQL> set autot on
SQL> select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18629 (1)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
6 recursive calls
0 db block gets
177413 consistent gets
176358 physical reads
23456 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> set autot off
再次查询物理读消失
SQL> set autot on
SQL> select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18629 (1)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
6 recursive calls
0 db block gets
177414 consistent gets
0 physical reads
23448 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> set autot off
这里有奇怪点,启用inmemory之后,flush buffer cache后,物理读非常大(基本上和逻辑读一样),不符合常理,因为inmemory和buffer cache是两个独立的东西,就算是flush buffer cache,也不应该导致in memory内的东西失效(而且从v$im_segments中查询是正常的),对于该问题百思不得其解,最后只好寻求inmemory邮件组和GCS帮忙.最终是由于并行相关参数配置导致该问题
SQL> alter system set parallel_force_local=false sid='*'
System altered.
SQL> alter system set parallel_degree_policy=AUTO sid='*'
System altered.
修改parallel_force_local和parallel_degree_policy后继续测试
SQL> select * from gv$im_segments where owner='CHF' and segment_name='XIFENFEI_888'
INST_ID OWNER SEGMENT_NAME PARTI SEGME TABLESPACE_NAME INMEMORY_SIZE BYTES BYTES_NOT_POPULATED POPULATE_ INMEMORY INMEMORY_DISTRI INMEMORY_DUPL INMEMORY_COMPRESS CON_ID
------- ----- --------------- ----- ----- --------------- ------------- ------------ ------------------- --------- -------- --------------- ------------- ----------------- ------
1 CHF XIFENFEI_888 TABLE RPT_DATA 1510211584 3571449856 1444610048 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
2 CHF XIFENFEI_888 TABLE RPT_DATA 1069481984 3571449856 2058321920 COMPLETED NONE AUTO NO DUPLICATE FOR QUERY LOW 0
SQL> set autot on
SQL> select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
set autot off
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18629 (1)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
6 recursive calls
0 db block gets
776 consistent gets
0 physical reads
0 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> alter system flush buffer_cache
2 ;
System altered.
SQL> /
System altered.
SQL>
SQL> set autot on
select /*+full(t)*/ count(*) from CHF.XIFENFEI_888 t;
set autot off
SQL>
COUNT(*)
----------
16883988
Execution Plan
----------------------------------------------------------
Plan hash value: 1642441725
---------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 18629 (1)| 00:00:01 | | | |
| 1 | SORT AGGREGATE | | 1 | | | | | |
| 2 | PX COORDINATOR | | | | | | | |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 1 | | | Q1,00 | P->S | QC (RAND) |
| 4 | SORT AGGREGATE | | 1 | | | Q1,00 | PCWP | |
| 5 | PX BLOCK ITERATOR | | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWC | |
| 6 | TABLE ACCESS INMEMORY FULL| XIFENFEI_888 | 16M| 18629 (1)| 00:00:01 | Q1,00 | PCWP | |
---------------------------------------------------------------------------------------------------------------------
Note
-----
- automatic DOP: Computed Degree of Parallelism is 2
- parallel scans affinitized for inmemory
Statistics
----------------------------------------------------------
6 recursive calls
0 db block gets
776 consistent gets
2 physical reads
0 redo size
545 bytes sent via SQL*Net to client
552 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
SQL> spool off
通过测试证明,在RAC环境中,如果要使用IN MEMORY特性,需要设置parallel_degree_policy=AUTO和parallel_force_local=false之后,才能够真正意义上的启动IM特性,不然只是执行计划中的启用,可能是假象
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标题：在ORACLE 12C RAC中使用in memory特性请注意parallel_degree_policy和parallel_force_local参数
作者：惜分飞