分类目录归档：ORACLE 12C

_use_single_log_writer和_max_outstanding_log_writes

发表于 2016 年 6 月 7 日 由 惜分飞

SCALABLE LGWR是12cR1中引入的一个令人激动的特性， 这是由于在OLTP环境中LGWR写日志往往成为系统的主要性能瓶颈， 如果LGWR进程能像DBWR(DBW0~DBWn)那样多进程（LGNN）写出redo到LOGFILE那么就可能大幅释放OLTP的并发能力，增长Transcation系统的单位时间事务处理能力。这里在12.2版本中进行测试，确定_use_single_log_writer和_max_outstanding_log_writes参数对于SCALABLE LGWR特性的影响
数据库版本

SQL> select * from v$version;

BANNER                                                                                         CON_ID
------------------------------------------------------------------------------------------ ----------
Oracle Database 12c Enterprise Edition Release 12.2.0.0.3 - 64bit Production                        0
PL/SQL Release 12.2.0.0.3 - Production                                                              0
CORE    12.2.0.0.3      Production                                                                  0
TNS for Linux: Version 12.2.0.0.3 - Production                                                      0
NLSRTL Version 12.2.0.0.3 - Production                                                              0

_use_single_log_writer和_max_outstanding_log_writes默认值

SQL> /
Enter value for param: _use_single_log_writer
old   6:    and upper(a.ksppinm) LIKE upper('%&param%')
new   6:    and upper(a.ksppinm) LIKE upper('%_use_single_log_writer%')

NAME                                                 VALUE                    DESCRIPTION
---------------------------------------------------- ------------------------ -------------------------------------------
_use_single_log_writer                               ADAPTIVE                 Use a single process for redo log writing

SQL> /
Enter value for param: _max_outstanding_log_writes
old   6:    and upper(a.ksppinm) LIKE upper('%&param%')
new   6:    and upper(a.ksppinm) LIKE upper('%_max_outstanding_log_writes%')

NAME                                                 VALUE                    DESCRIPTION
---------------------------------------------------- ------------------------ ----------------------------------------------
_max_outstanding_log_writes                          2                        Maximum number of outstanding redo log writes

lg进程数量
这里可以看出来，有一个lgwr进程，两个lg进程和_max_outstanding_log_writes参数配置匹配

[oracle@ora1221 ~]$ ps -ef|grep ora_lg
oracle    49790      1  0 10:32 ?        00:00:00 ora_lgwr_orcl12c2
oracle    49794      1  0 10:32 ?        00:00:00 ora_lg00_orcl12c2
oracle    49798      1  0 10:32 ?        00:00:00 ora_lg01_orcl12c2

修改_max_outstanding_log_writes参数
通过修改_max_outstanding_log_writes参数为4，发现lg进程数量也变为了4，证明_max_outstanding_log_writes进程决定lg进程数量

SQL> alter system set "_max_outstanding_log_writes"=4 ;     
alter system set "_max_outstanding_log_writes"=4
                 *
ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified


SQL> alter system set "_max_outstanding_log_writes"=4 scope=spfile;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 2516582400 bytes
Fixed Size                  8260048 bytes
Variable Size             671090224 bytes
Database Buffers         1828716544 bytes
Redo Buffers                8515584 bytes
Database mounted.
Database opened.
SQL> exit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.0.3 - 64bit Production
[oracle@ora1221 ~]$ ps -ef|grep lg
oracle    72339      1  0 13:45 ?        00:00:00 ora_lgwr_orcl12c2
oracle    72343      1  0 13:45 ?        00:00:00 ora_lg00_orcl12c2
oracle    72347      1  0 13:45 ?        00:00:00 ora_lg01_orcl12c2
oracle    72351      1  0 13:45 ?        00:00:00 ora_lg02_orcl12c2
oracle    72359      1  0 13:45 ?        00:00:00 ora_lg03_orcl12c2

修改_use_single_log_writer参数
通过测试_use_single_log_writer参数修改，我们可以确定_use_single_log_writer修改为true后，数据库恢复到12c之前的lgwr管理方式

[oracle@ora1221 ~]$ ss

SQL*Plus: Release 12.2.0.0.3 Production on Thu Aug 6 13:45:33 2015

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.0.3 - 64bit Production

SQL> alter system set "_use_single_log_writer"=1 ;     
alter system set "_use_single_log_writer"=1
                 *
ERROR at line 1:
ORA-02095: specified initialization parameter cannot be modified


SQL>  alter system set "_use_single_log_writer"=1 scope=spfile;
 alter system set "_use_single_log_writer"=1 scope=spfile
*
ERROR at line 1:
ORA-00096: invalid value 1 for parameter _use_single_log_writer, must be from
among ADAPTIVE, FALSE, TRUE


SQL> alter system set "_use_single_log_writer"=TRUE scope=spfile;

System altered.

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> exit
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.0.3 - 64bit Production
[oracle@ora1221 ~]$ ps -ef|grep lg
oracle    72702  71510  0 13:46 pts/0    00:00:00 grep lg
[oracle@ora1221 ~]$ ss

SQL*Plus: Release 12.2.0.0.3 Production on Thu Aug 6 13:46:50 2015

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to an idle instance.

SQL> startup
ORACLE instance started.

Total System Global Area 2516582400 bytes
Fixed Size                  8260048 bytes
Variable Size             671090224 bytes
Database Buffers         1828716544 bytes
Redo Buffers                8515584 bytes
Database mounted.
Database opened.
SQL> exit   
Disconnected from Oracle Database 12c Enterprise Edition Release 12.2.0.0.3 - 64bit Production
[oracle@ora1221 ~]$ ps -ef|grep lg
oracle    72754      1  0 13:46 ?        00:00:00 ora_lgwr_orcl12c2
oracle    73008  71510  0 13:47 pts/0    00:00:00 grep lg

从这里可以确定_use_single_log_writer确定是否启用SCALABLE LGWR(多个lg子进程),_max_outstanding_log_writes确定lg进程个数

发表在 ORACLE 12C | 标签为 , , | 评论关闭

Oracle 12C Active Data Guard Far Sync 配置

发表于 2015 年 11 月 5 日 由 惜分飞

Active Data Guard Far Sync是Oracle 12c的新功能（也称为Far Sync Standby），Far Sync功能的实现是通过在距离主库(Primary Database)相对较近的地点配置Far Sync实例，主库(Primary Database) 同步(synchronous)传输redo到Far Sync实例，然后Far Sync实例再将redo异步(asynchronous)传输到终端备库(Standby Database)。这样既可以保证零数据丢失又可以降低主库压力。Far Sync实例只有密码文件，init参数文件和控制文件，而没有数据文件。 如果redo 传输采用Maximum Availability模式，我们可以在距离生产中心(Primary Database)相对较近的地点配置Far Sync实例，主库(Primary Database)同步(synchronous)传输redo到Far Sync实例，保证零数据丢失（zero data loss），同时主库和Far Sync距离较近，网络延时很小，因此对主库性能影响很小。然后Far Sync实例再将redo异步(asynchronous)发送到终端备库(Standby Database)。 如果redo 传输采用Maximum Performance模式，我们可以在距离生产中心(Primary Database)相对较近的地点配置Far Sync实例，主库(Primary Database) 异步传输redo到Far Sync实例，然后Far Sync实例再负责传输redo到其他多个终端备库(Standby Database)。这样可以减少主库向多个终端备库(Standby Database)传输redo的压力（offload）。 Far Sync配置对于Data Guard 角色转换(role transitions)是透明的，即switchover/failover命令方式与12c之前相同。
1.主库配置fra

SQL> alter system set DB_RECOVERY_FILE_DEST_SIZE=200G;

System altered.

SQL> alter system set db_recovery_file_dest='/u01/app/oracle/fast_recovery_area';

System altered.

2.启用归档模式和强制日志

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area 2516582400 bytes
Fixed Size                  4585912 bytes
Variable Size             671090248 bytes
Database Buffers         1828716544 bytes
Redo Buffers               12189696 bytes
Database mounted.
SQL> alter database archivelog;

Database altered.

SQL> alter database force logging;

Database altered.

SQL> alter database open;

Database altered.

3.主机规划

192.168.137.121  ora1221   --->主库(ORCL12C)
192.168.137.122  ora1222   --->Far Sync实例(ORCL12CFS)
192.168.137.123  ora1223   --->备库(ORCL12CDG)

4.tns配置

ORCL12C =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = ora1221)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl12c)
    )
  )

ORCL12CDG =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = ora1223)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl12c)
    )
  )

ORCL12CFS =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = ora1222)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = orcl12c)
    )
  )

5.参数文件配置

--主库
db_unique_name='orcl12c'
service_names='orcl12c'
log_archive_dest_1='LOCATION=USE_DB_RECOVERY_FILE_DEST valid_for=(all_logfiles,all_roles) db_unique_name=orcl12c'
log_archive_dest_2='service=orcl12cfs lgwr  sync  AFFIRM MAX_FAILURE=1 ALTERNATE=LOG_ARCHIVE_DEST_3 valid_for=(online_logfiles,primary_role) db_unique_name=orcl12cfs'
LOG_ARCHIVE_DEST_3='SERVICE=orcl12cdg  lgwr ASYNC ALTERNATE=LOG_ARCHIVE_DEST_2 VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=orcl12cdg'
LOG_ARCHIVE_DEST_STATE_3=ALTERNATE
log_archive_config='dg_config=(orcl12c,orcl12cdg,orcl12cfs)'
standby_file_management=auto
db_file_name_convert='/u01/app/oracle/oradata/orcl12c/','/u01/app/oracle/oradata/orcl12c/'
log_file_name_convert='/u01/app/oracle/oradata/orcl12c/','/u01/app/oracle/oradata/orcl12c/'
fal_server='orcl12cdg','orcl12cfs'

--Far Sync实例
db_unique_name='orcl12cfs'
service_names='orcl12c'
log_archive_dest_1='LOCATION=USE_DB_RECOVERY_FILE_DEST valid_for=(all_logfiles,all_roles) db_unique_name=orcl12cfs'
log_archive_dest_2='service=orcl12cdg lgwr  async valid_for=(STANDBY_LOGFILES,STANDBY_ROLE) db_unique_name=orcl12cdg'
log_archive_config='dg_config=(orcl12c,orcl12cdg,orcl12cfs)'
standby_file_management=manual
fal_server='orcl12c'

--备库
db_unique_name='orcl12cdg'
service_names='orcl12c'
log_archive_dest_1='LOCATION=USE_DB_RECOVERY_FILE_DEST valid_for=(all_logfiles,all_roles) db_unique_name=orcl12cdg'
log_archive_dest_2='service=orcl12c lgwr  async   valid_for=(online_logfiles,primary_role) db_unique_name=orcl12c'
log_archive_config='dg_config=(orcl12c,orcl12cdg,orcl12cfs)'
standby_file_management=auto
db_file_name_convert='/u01/app/oracle/oradata/orcl12c/','/u01/app/oracle/oradata/orcl12c/'
log_file_name_convert='/u01/app/oracle/oradata/orcl12c/','/u01/app/oracle/oradata/orcl12c/'
fal_server='orcl12c','orcl12cfs'

6.密码文件
拷贝主库的密码文件到Far Sync实例和备库$ORACLE_HOME/dbs下(如果是win在%ORACLE_HOME%/database中)

7.创建Far Sync实例
创建和参数文件匹配的fra,adump目录

--主库
ALTER DATABASE CREATE FAR SYNC INSTANCE CONTROLFILE AS '/tmp/controlfs01.ctl';
拷贝到Far Sync实例对应的控制文件位置

--Far Sync实例
startup pfile='/tmp/pfile' mount

ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 10 '/u01/app/oracle/oradata/orcl12c/std_redo10.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 11 '/u01/app/oracle/oradata/orcl12c/std_redo11.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 12 '/u01/app/oracle/oradata/orcl12c/std_redo12.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 13 '/u01/app/oracle/oradata/orcl12c/std_redo13.log' size 50m reuse;

ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT  LOGFILE DISCONNECT FROM SESSION;

8.创建备库
创建和参数文件匹配的fra,adump目录

--主库备份（传输至备库）
backup database format '/tmp/ora12c_%U';

--主库创建standby ctl（传输至备库和备库参数文件路径一致）
alter database create standby controlfile as '/tmp/controlst.ctl';

--启动备库至mount
startup pfile='/tmp/pfile' mount;

--备库注册备份
catalog start with '/tmp/xifenfei/';

--备库还原数据文件并恢复
restore database;
recover database;

--增加standby redo
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 10 '/u01/app/oracle/oradata/orcl12c/std_redo10.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 11 '/u01/app/oracle/oradata/orcl12c/std_redo11.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 12 '/u01/app/oracle/oradata/orcl12c/std_redo12.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 13 '/u01/app/oracle/oradata/orcl12c/std_redo13.log' size 50m reuse;

--备库开启mrp进程
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT  LOGFILE DISCONNECT FROM SESSION;

--主库增加standby redo
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 10 '/u01/app/oracle/oradata/orcl12c/std_redo10.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 11 '/u01/app/oracle/oradata/orcl12c/std_redo11.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 12 '/u01/app/oracle/oradata/orcl12c/std_redo12.log' size 50m reuse;
ALTER DATABASE ADD STANDBY LOGFILE thread 1  GROUP 13 '/u01/app/oracle/oradata/orcl12c/std_redo13.log' size 50m reuse;

9.配置结果

SQL> select * from V$DATAGUARD_CONFIG;

DB_UNIQUE_NAME                 PARENT_DBUN                    DEST_ROLE         CURRENT_SCN     CON_ID
------------------------------ ------------------------------ ----------------- ----------- ----------
orcl12c                        NONE                           PRIMARY DATABASE      1950551          0
orcl12cfs                      orcl12c                        FAR SYNC INSTANCE     1950390          0
orcl12cdg                      orcl12cfs                      PHYSICAL STANDBY      1950390          0

SQL> select group#, status, thread#, sequence#, first_change#, next_change# from v$standby_log;

    GROUP# STATUS        THREAD#  SEQUENCE# FIRST_CHANGE# NEXT_CHANGE#
---------- ---------- ---------- ---------- ------------- ------------
        10 ACTIVE              1         27       1863140
        11 UNASSIGNED          1          0
        12 UNASSIGNED          1          0
        13 UNASSIGNED          1          0

SQL> select PROTECTION_MODE,PROTECTION_LEVEL from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM PERFORMANCE  MAXIMUM PERFORMANCE

10.调整保护级别
从MAXIMUM PERFORMANCE调整为MAXIMUM AVAILABILITY

--主库
SQL> startup mount;
ORACLE instance started.

Total System Global Area 2516582400 bytes
Fixed Size                  4585912 bytes
Variable Size             671090248 bytes
Database Buffers         1828716544 bytes
Redo Buffers               12189696 bytes
Database mounted.
SQL> alter database set standby database to maximize availability;

Database altered.

SQL>  select PROTECTION_MODE,PROTECTION_LEVEL from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY UNPROTECTED

SQL> alter database open;

Database altered.

SQL>  select PROTECTION_MODE,PROTECTION_LEVEL from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY

--Far Sync实例
SQL>  select PROTECTION_MODE,PROTECTION_LEVEL from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY MAXIMUM AVAILABILITY

--备库
SQL> select PROTECTION_MODE,PROTECTION_LEVEL from v$database;

PROTECTION_MODE      PROTECTION_LEVEL
-------------------- --------------------
MAXIMUM AVAILABILITY RESYNCHRONIZATION
发表在 Data Guard, ORACLE 12C | 标签为 , , | 评论关闭

在ORACLE 12C RAC中使用in memory特性请注意parallel_degree_policy和parallel_force_local参数

发表于 2015 年 5 月 27 日 由 惜分飞

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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