[20180316]共享服务模式和直接路径读.txt

[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;