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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