Exadata:Smart Scan(二) FAST FULL SCAN

实测了以下Exadata smart scan对于INDEX STORAGE FAST FULL SCAN似乎实际并不生效,详见以下测试。不仅普通的B*tree index也包括compressed index、reverse key index等类型。

Why is my Exadata smart scan not offloading?
Exadata Smart Scan and Index Access 

上面2篇文章介绍了了类似的XD offload 对index fast full scan不生效的问题, 相关的BUG有:

Bug 8257122 – Exadata smart scan caching does not work for INDEX FAST FULL scan (Doc ID 8257122.8)

 

以下测试了对NORMAL INDEX和bitmap index fast full scan的OFFLOAD情况:

SQL> select blocks,bytes/1024/1024/1024 from dba_segments where segment_name='LARGE_TABLE';
BLOCKS BYTES/1024/1024/1024
---------- --------------------
7127040               54.375
Elapsed: 00:00:00.19
SQL> alter system flush buffer_cache;
System altered.
Elapsed: 00:00:00.19
SQL>  select count(*) from  LARGE_TABLE where object_id between 1000 and 20000;
COUNT(*)
----------
486735872
Elapsed: 00:00:23.29
SQL> alter system flush buffer_cache;
System altered.
Elapsed: 00:00:00.19
SQL> select  /*+ OPT_PARAM('cell_offload_processing' 'false') */ count(*) from  LARGE_TABLE where object_id between 1000 and 20000;
COUNT(*)
----------
486735872
Elapsed: 00:03:24.22
SQL> create index pk_lt on large_table (object_id,data_object_id) tablespace larget parallel nologging;
Index created.
Elapsed: 00:01:14.18
SQL> alter index pk_lt noparallel;
Index altered.
SQL> exec dbms_stats.gather_table_stats('SYS','LARGE_TABLE',cascade=>TRUE, estimate_percent=>100, degree=>8);
PL/SQL procedure successfully completed.
Elapsed: 00:13:12.61
select a.name,b.value 
from v$sysstat a , v$mystat b
where
a.statistic#=b.statistic#
and (a.name in ('physical read total bytes','physical write total bytes',
'cell IO uncompressed bytes') or a.name like 'cell phy%' );
NAME                                                                  VALUE
---------------------------------------------------------------- ----------
physical read total bytes                                                 0
physical write total bytes                                                0
cell physical IO interconnect bytes                                       0
cell physical IO bytes saved during optimized file creation               0
cell physical IO bytes saved during optimized RMAN file restore           0
cell physical IO bytes eligible for predicate offload                     0
cell physical IO bytes saved by storage index                             0
cell physical IO bytes sent directly to DB node to balance CPU            0
cell physical IO interconnect bytes returned by smart scan                0
cell IO uncompressed bytes                                                0
10 rows selected.
alter system flush buffer_cache;
set timing on;
set linesize 200 pagesize 2000 
select /*+ FULL(LARGE_TABLE) */ count(*) from  LARGE_TABLE where object_id between 1000 and 20000;
COUNT(*)
----------
486735872
Elapsed: 00:00:23.30
TABLE ACCESS STORAGE FULL| LARGE_TABLE |   403M|  1925M|  1935K  (1)|
SQL> select a.name,b.value 
2  from v$sysstat a , v$mystat b
3  where
a.statistic#=b.statistic#
and (a.name in ('physical read total bytes','physical write total bytes',
'cell IO uncompressed bytes') or a.name like 'cell phy%' );  4    5    6  
NAME                                                                  VALUE
---------------------------------------------------------------- ----------
physical read total bytes                                        5.8303E+10
physical write total bytes                                                0
cell physical IO interconnect bytes                              6055421032
cell physical IO bytes saved during optimized file creation               0
cell physical IO bytes saved during optimized RMAN file restore           0
cell physical IO bytes eligible for predicate offload            5.8303E+10
cell physical IO bytes saved by storage index                             0
cell physical IO bytes sent directly to DB node to balance CPU            0
cell physical IO interconnect bytes returned by smart scan       6055396456
cell IO uncompressed bytes                                       5.8321E+10
10 rows selected.
Elapsed: 00:00:00.01
SQL> 
SQL> alter system flush buffer_cache;
set timing on;
set linesize 200 pagesize 2000 
System altered.
SQL> SQL> 
SQL> 
SQL> explain plan for select count(*) from  LARGE_TABLE where object_id between 1000 and 20000;
Explained.
Elapsed: 00:00:00.02
SQL> @?/rdbms/admin/utlxplp
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 800139279
---------------------------------------------------------------------------------------
| Id  | Operation                     | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |       |     1 |     5 |   356K  (1)| 00:00:14 |
|   1 |  SORT AGGREGATE               |       |     1 |     5 |            |          |
|*  2 |   INDEX STORAGE FAST FULL SCAN| PK_LT |   403M|  1925M|   356K  (1)| 00:00:14 |
---------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - storage("OBJECT_ID"<=20000 AND "OBJECT_ID">=1000)
filter("OBJECT_ID"<=20000 AND "OBJECT_ID">=1000)
15 rows selected.
Elapsed: 00:00:00.02
SQL> select count(*) from  LARGE_TABLE where object_id between 1000 and 20000;
COUNT(*)
----------
486735872
Elapsed: 00:02:01.66
SQL> oradebug tracefile_name
/u01/app/oracle/diag/rdbms/orcl/orcl1/trace/orcl1_ora_39539.trc
SQL> select a.name,b.value 
2  from v$sysstat a , v$mystat b
3  where
a.statistic#=b.statistic#
and (a.name in ('physical read total bytes','physical write total bytes',
'cell IO uncompressed bytes') or a.name like 'cell phy%' );  4    5    6  
NAME                                                                  VALUE
---------------------------------------------------------------- ----------
physical read total bytes                                        1.3300E+10
physical write total bytes                                                0
cell physical IO interconnect bytes                              1.3300E+10
cell physical IO bytes saved during optimized file creation               0
cell physical IO bytes saved during optimized RMAN file restore           0
cell physical IO bytes eligible for predicate offload                     0
cell physical IO bytes saved by storage index                             0
cell physical IO bytes sent directly to DB node to balance CPU            0
cell physical IO interconnect bytes returned by smart scan                0
cell IO uncompressed bytes                                                0
10 rows selected.
Elapsed: 00:00:00.01
END OF STMT
PARSE #47310019587768:c=2000,e=2137,p=0,cr=0,cu=0,mis=1,r=0,dep=0,og=1,plh=800139279,tim=1353385966411213
EXEC #47310019587768:c=1000,e=67,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,plh=800139279,tim=1353385966411365
WAIT #47310019587768: nam='SQL*Net message to client' ela= 3 driver id=1650815232 #bytes=1 p3=0 obj#=-1 tim=1353385966411401
WAIT #47310019587768: nam='cell single block physical read' ela= 511 cellhash#=451279719 diskhash#=3519799300 bytes=8192 obj#=25183 tim=1353385966414839
WAIT #47310019587768: nam='cell multiblock physical read' ela= 16720 cellhash#=451279719 diskhash#=3519799300 bytes=1048576 obj#=25183 tim=1353385966433058
WAIT #47310019587768: nam='cell multiblock physical read' ela= 2965 cellhash#=451279719 diskhash#=3519799300 bytes=1048576 obj#=25183 tim=1353385966440986
...........................
select count(*) from  LARGE_TABLE where owner like '%SY%';
QL> explain plan for select count(*) from  LARGE_TABLE where owner like '%SY%';
Explained.
Elapsed: 00:00:00.00
SQL> @?/rdbms/admin/utlxplp
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 3706014413
------------------------------------------------------------------------------------------------
| Id  | Operation                             | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                      |        |     1 |     5 | 19017   (1)| 00:00:01 |
|   1 |  SORT AGGREGATE                       |        |     1 |     5 |            |          |
|   2 |   BITMAP CONVERSION COUNT             |        |    26M|   127M| 19017   (1)| 00:00:01 |
|*  3 |    BITMAP INDEX STORAGE FAST FULL SCAN| BIT_LT |       |       |            |          |
------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - storage("OWNER" LIKE '%SY%' AND "OWNER" IS NOT NULL)
filter("OWNER" LIKE '%SY%' AND "OWNER" IS NOT NULL)
16 rows selected.
Elapsed: 00:00:00.01
SQL> set linesize 200 pagesize 2000 
SQL> select count(*) from  LARGE_TABLE where owner like '%SY%';
COUNT(*)
----------
362643456
Elapsed: 00:00:01.07
SQL> select a.name,b.value 
2  from v$sysstat a , v$mystat b
3  where
a.statistic#=b.statistic#
and (a.name in ('physical read total bytes','physical write total bytes',
'cell IO uncompressed bytes') or a.name like 'cell phy%' );  4    5    6  
NAME                                                                  VALUE
---------------------------------------------------------------- ----------
physical read total bytes                                         173424640
physical write total bytes                                                0
cell physical IO interconnect bytes                               173424640
cell physical IO bytes saved during optimized file creation               0
cell physical IO bytes saved during optimized RMAN file restore           0
cell physical IO bytes eligible for predicate offload                     0
cell physical IO bytes saved by storage index                             0
cell physical IO bytes sent directly to DB node to balance CPU            0
cell physical IO interconnect bytes returned by smart scan                0
cell IO uncompressed bytes                                                0
10 rows selected.
Elapsed: 00:00:00.02
SQL> 

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