[20180316]共享服务模式和直接路径读.txt
--//在共享服务器模式下,执行计划不会选择直接路径读,通过例子证明.
1.环境:
SYS@book> @ &r/ver1
PORT_STRING VERSION BANNER
-------------------- ---------- ----------------------------------------------------------------------------
x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
SYS@book> alter system set filesystemio_options=asynch scope=spfile;
System altered.
--//重启数据库.
SCOTT@book> show sga
Total System Global Area 634732544 bytes
Fixed Size 2255792 bytes
Variable Size 197133392 bytes
Database Buffers 427819008 bytes
Redo Buffers 7524352 bytes
SCOTT@book> create table t as select rownum id from dual connect by level<=2;
Table created.
SCOTT@book> ALTER TABLE t MINIMIZE RECORDS_PER_BLOCK ;
Table altered.
--//这样可以实现每块2条记录.
SCOTT@book> insert into t select rownum+2 from dual connect by level <=8e4-2;
79998 rows created.
SCOTT@book> commit ;
Commit complete.
--//分析表略.
SCOTT@book> select OWNER,SEGMENT_NAME,SEGMENT_TYPE,HEADER_FILE,HEADER_BLOCK,BYTES,BLOCKS from dba_segments where owner=user and segment_name='T';
OWNER SEGMENT_NAME SEGMENT_TYPE HEADER_FILE HEADER_BLOCK BYTES BLOCKS
------ -------------------- ------------------ ----------- ------------ ---------- ----------
SCOTT T TABLE 4 546 333447168 40704
--//占用 333447168/1024/1024 = 318M
SCOTT@book> select object_id,data_object_id from dba_objects where owner=user and object_name='T';
OBJECT_ID DATA_OBJECT_ID
---------- --------------
90467 90467
SCOTT@book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
36020
2.测试分析:
SCOTT@book> alter system flush buffer_cache;
System altered.
SCOTT@book> alter session set statistics_level=all;
Session altered.
SCOTT@book> @ &r/spid
SID SERIAL# PROCESS SERVER SPID PID P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
274 11 46995 DEDICATED 46996 21 6 alter system kill session '274,11' immediate;
--//server=DEDICATED采用专用模式.
SCOTT@book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
0
SCOTT@book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
------------------------------------------ ---------- ---------- ----------
physical reads direct 97 0 274
physical reads direct temporary tablespace 110 0 274
physical reads direct (lob) 176 0 274
SCOTT@book> select count(*) from t;
COUNT(*)
----------
80000
SCOTT@book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
------------------------------------------ ---------- ---------- ----------
physical reads direct 97 40217 274
physical reads direct temporary tablespace 110 0 274
physical reads direct (lob) 176 0 274
--//可以发现执行计划走的physical reads direct.physical reads direct=40217.通过执行后数据缓存数量也可以推定:
SCOTT@book> alter system flush buffer_cache;
System altered.
SCOTT@book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
0
SCOTT@book> select count(*) from t;
COUNT(*)
----------
80000
SCOTT@book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID cyzznbykb509s, child number 0
-------------------------------------
select count(*) from t
Plan hash value: 2966233522
----------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | Reads |
----------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 10963 (100)| | 1 |00:00:00.17 | 40227 | 40222 |
| 1 | SORT AGGREGATE | | 1 | 1 | | | 1 |00:00:00.17 | 40227 | 40222 |
| 2 | TABLE ACCESS FULL| T | 1 | 89876 | 10963 (1)| 00:02:12 | 80000 |00:00:00.17 | 40227 | 40222 |
----------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / T@SEL$1
Note
-----
- dynamic sampling used for this statement (level=2)
SCOTT@book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
5
--//仅仅缓存5个数据块.
3.测试分析:
$ rlsql scott/book@127.0.0.1:1521/book
--//我以前多次提到dispatchers包括服务.ezconenct优先使用共享服务器模式:
SCOTT@127.0.0.1:1521/book> show parameter dispatchers
NAME TYPE VALUE
--------------- -------- -------------------------------------
dispatchers string (PROTOCOL=TCP) (SERVICE=book,bookXDB)
max_dispatchers integer
SCOTT@127.0.0.1:1521/book> alter session set statistics_level=all;
Session altered.
SCOTT@127.0.0.1:1521/book> alter system flush buffer_cache;
System altered.
SCOTT@127.0.0.1:1521/book> @ &r/spid
SID SERIAL# PROCESS SERVER SPID PID P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
261 1 47005 SHARED 46300 20 1 alter system kill session '261,1' immediate;
--//server=SHARED,采用共享服务器模式.
SCOTT@127.0.0.1:1521/book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
------------------------------------------ ---------- ---------- ----------
physical reads direct 97 0 261
physical reads direct temporary tablespace 110 0 261
physical reads direct (lob) 176 0 261
SCOTT@127.0.0.1:1521/book> select count(*) from t;
COUNT(*)
----------
80000
SCOTT@127.0.0.1:1521/book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
---------------------------------------------------------------------- ---------- ---------- ----------
physical reads direct 97 0 261
physical reads direct temporary tablespace 110 0 261
physical reads direct (lob) 176 0 261
--//可以发现在共享服务器模式下执行计划不选择直接路径读.通过缓存数量也可以证明:
SCOTT@127.0.0.1:1521/book> alter system flush buffer_cache;
System altered.
SCOTT@127.0.0.1:1521/book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
0
SCOTT@127.0.0.1:1521/book> select count(*) from t;
COUNT(*)
----------
80000
SCOTT@127.0.0.1:1521/book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID cyzznbykb509s, child number 0
-------------------------------------
select count(*) from t
Plan hash value: 2966233522
----------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | Cost (%CPU)| E-Time | A-Rows | A-Time | Buffers | Reads |
----------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 10963 (100)| | 1 |00:00:00.34 | 40236 | 40222 |
| 1 | SORT AGGREGATE | | 1 | 1 | | | 1 |00:00:00.34 | 40236 | 40222 |
| 2 | TABLE ACCESS FULL| T | 1 | 89876 | 10963 (1)| 00:02:12 | 80000 |00:00:00.34 | 40236 | 40222 |
----------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
2 - SEL$1 / T@SEL$1
Note
-----
- dynamic sampling used for this statement (level=2)
SCOTT@127.0.0.1:1521/book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
40222
--//全表扫描后数据块大量进入数据缓存.
3.但是在并行的情况下共享模式情况就不同:
SCOTT@127.0.0.1:1521/book> @ &r/spid
SID SERIAL# PROCESS SERVER SPID PID P_SERIAL# C50
---------- ---------- ------------------------ --------- ------ ------- ---------- --------------------------------------------------
261 1 47005 SHARED 46300 20 1 alter system kill session '261,1' immediate;
SCOTT@127.0.0.1:1521/book> alter system flush buffer_cache;
System altered.
SCOTT@127.0.0.1:1521/book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
0
SCOTT@127.0.0.1:1521/book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
---------------------------------------------------------------------- ---------- ---------- ----------
physical reads direct 97 0 261
physical reads direct temporary tablespace 110 0 261
physical reads direct (lob) 176 0 261
SCOTT@127.0.0.1:1521/book> select /*+ parallel(t 8) */ count(*) from t;
COUNT(*)
----------
80000
SCOTT@127.0.0.1:1521/book> @ &r/dpc '' ''
PLAN_TABLE_OUTPUT
-------------------------------------
SQL_ID 965gv5rh77t0c, child number 0
-------------------------------------
select /*+ parallel(t 8) */ count(*) from t
Plan hash value: 3126468333
--------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | Cost (%CPU)| E-Time | TQ |IN-OUT| PQ Distrib | A-Rows | A-Time | Buffers |
--------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1522 (100)| | | | | 1 |00:00:00.22 | 15 |
| 1 | SORT AGGREGATE | | 1 | 1 | | | | | | 1 |00:00:00.22 | 15 |
| 2 | PX COORDINATOR | | 1 | | | | | | | 8 |00:00:00.22 | 15 |
| 3 | PX SEND QC (RANDOM) | :TQ10000 | 0 | 1 | | | Q1,00 | P->S | QC (RAND) | 0 |00:00:00.01 | 0 |
| 4 | SORT AGGREGATE | | 0 | 1 | | | Q1,00 | PCWP | | 0 |00:00:00.01 | 0 |
| 5 | PX BLOCK ITERATOR | | 0 | 89876 | 1522 (0)| 00:00:19 | Q1,00 | PCWC | | 0 |00:00:00.01 | 0 |
|* 6 | TABLE ACCESS FULL| T | 0 | 89876 | 1522 (0)| 00:00:19 | Q1,00 | PCWP | | 0 |00:00:00.01 | 0 |
--------------------------------------------------------------------------------------------------------------------------------------------------
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1
6 - SEL$1 / T@SEL$1
Predicate Information (identified by operation id):
---------------------------------------------------
6 - access(:Z>=:Z AND :Z<=:Z)
Note
-----
- dynamic sampling used for this statement (level=2)
SCOTT@127.0.0.1:1521/book> @ &r/viewsess "physical reads direct"
NAME STATISTIC# VALUE SID
------------------------------------------ ---------- ---------- ----------
physical reads direct 97 40217 261
physical reads direct temporary tablespace 110 0 261
physical reads direct (lob) 176 0 261
--//可以发现physical reads direct上升.
SCOTT@127.0.0.1:1521/book> select count(*) from v$bh where OBJD=90467 and STATUS<>'free';
COUNT(*)
----------
314
--//从数据缓存的数量也可以看出.
4.附上viewsess.sql脚本:
set verify off
column name format a70
SELECT b.NAME, a.statistic#, a.VALUE,a.sid
FROM v$mystat a, v$statname b
WHERE lower(b.NAME) like lower('%&1%') AND a.statistic# = b.statistic# ;
--and a.value>0;