statement suspended, wait error to be cleared

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：statement suspended, wait error to be cleared

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

一、现场报告
导入数据到Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX的时候，hang住了，求救

[oracle@TestServer-RHAS-5 dmpdir]$ impdp system/ DIRECTORY=dmpdir DUMPFILE=cscnew.20111123.dmp LOGFILE=cscnew.20111123.log SCHEMAS=CSCNEW remap_schema=CSCNEW:TESTB remap_tablespace=CSC_TAB_1:TESTB table_exists_action=replace
…………
. . imported "TESTB"."TAB_CS_SELF_WORKTIME"                  0 KB       0 rows
. . imported "TESTB"."TAB_CS_SELF_WORKTIME_DETAIL"           0 KB       0 rows
. . imported "TESTB"."TAB_CS_USERMENU"                       0 KB       0 rows
. . imported "TESTB"."TAB_PUB_BANK"                          0 KB       0 rows
. . imported "TESTB"."TAB_PUB_BUSISRVINFO"                   0 KB       0 rows
. . imported "TESTB"."TAB_PUB_CONTACT"                       0 KB       0 rows
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX

二、处理过程
1、分析是否是impdp是否因为网络等情况终止掉

[oracle@TestServer-RHAS-5 ~]$ ps -ef|grep impdp
oracle    2520  1837  0 09:59 pts/8    00:00:00 grep impdp
oracle   23819 20966  0 09:39 pts/6    00:00:00 impdp         DIRECTORY=dmpdir DUMPFILE=cscnew.20111123.dmp LOGFILE=cscnew.20111123.log SCHEMAS=CSCNEW remap_schema=CSCNEW:TESTB remap_tablespace=CSC_TAB_1:TESTB table_exists_action=replace
[oracle@TestServer-RHAS-5 ~]$ ps -ef|grep LOCAL=YES
oracle    2692  1837  0 10:00 pts/8    00:00:00 grep LOCAL=YES
oracle   10754 10694  0 09:15 ?        00:00:09 oraclemcrm (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))
oracle   23835 23819  0 09:40 ?        00:00:00 oraclemcrm (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))

通过上面的查询，证明impdp进程工作正常

2、查询等待事件

[oracle@TestServer-RHAS-5 ~]$ sqlplus / as sysdba
SQL*Plus: Release 10.2.0.4.0 - Production on Thu Nov 24 10:00:26 2011
Copyright (c) 1982, 2007, Oracle.  All Rights Reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> select event from v$session_wait where wait_class#<>6;
EVENT
----------------------------------------------------------------
SQL*Net message to client
statement suspended, wait error to be cleared

通过这个查询，发现一个异常等待事件:statement suspended, wait error to be cleared。
查询MOS，确定是表空间不足引起impdp suspended
Statement Suspended, Wait Error To Be Cleared Wait Event [ID 761848.1]

Oracle Database provides a means for suspending, and later resuming,
the execution of large database operations in the event of space allocation failures.
This enables you to take corrective action instead of the Oracle Database server returning an error to the user.
After the error condition is corrected, the suspended operation automatically resumes.
This feature is called resumable space allocation. The statements that are affected are called resumable statements.
The time between suspending the execution till correction of the error is reported as
"statement suspended, wait error to be cleared" wait event.

3、查看alert.log日志文件确认

[oracle@TestServer-RHAS-5 ~]$ cd /opt/oracle/admin/mcrm/bdump/
[oracle@TestServer-RHAS-5 bdump]$ tail -30 alert_mcrm.log
Thu Nov 24 09:29:20 2011
create tablespace testb
datafile '/opt/oradata/mcrm/testb.dbf'
size 1500M autoextend on next 50M maxsize 2000M
Thu Nov 24 09:29:51 2011
Completed: create tablespace testb
datafile '/opt/oradata/mcrm/testb.dbf'
size 1500M autoextend on next 50M maxsize 2000M
Thu Nov 24 09:40:00 2011
The value (30) of MAXTRANS parameter ignored.
kupprdp: master process DM00 started with pid=111, OS id=23858
         to execute - SYS.KUPM$MCP.MAIN('SYS_IMPORT_SCHEMA_01', 'SYSTEM', 'KUPC$C_1_20111124094000', 'KUPC$S_1_20111124094000', 0);
kupprdp: worker process DW01 started with worker id=1, pid=112, OS id=23870
         to execute - SYS.KUPW$WORKER.MAIN('SYS_IMPORT_SCHEMA_01', 'SYSTEM');
Thu Nov 24 09:43:11 2011
statement in resumable session 'SYSTEM.SYS_IMPORT_SCHEMA_01.1' was suspended due to
    ORA-01652: unable to extend temp segment by 128 in tablespace TESTB
Thu Nov 24 10:00:45 2011
Thread 1 advanced to log sequence 4761 (LGWR switch)
  Current log# 3 seq# 4761 mem# 0: /opt/oradata/mcrm/redo03.log

4、查询TESTB表空间使用情况

SQL> select bytes/1024/1024,maxbytes/1024/1024,user_bytes/1024/1024
  2  from dba_data_files where tablespace_name='TESTB';
BYTES/1024/1024 MAXBYTES/1024/1024 USER_BYTES/1024/1024
--------------- ------------------ --------------------
           2000               2000            1998.9375

5、解决问题

Thu Nov 24 10:04:21 2011
alter tablespace TESTB add datafile '/opt/oradata/mcrm/testb01.dbf' size 100m  autoextend on next 1m maxsize 30g
Thu Nov 24 10:04:25 2011
Completed: alter tablespace TESTB add datafile '/opt/oradata/mcrm/testb01.dbf' size 100m  autoextend on next 1m maxsize 30g
Thu Nov 24 10:04:26 2011
statement in resumable session 'SYSTEM.SYS_IMPORT_SCHEMA_01.1' was resumed

通过这个日志可以看出，表空间不足的问题解决后（可以添加数据文件，或者resize数据文件大小），impdp的job又开始运行

cursor: pin S事件

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：cursor: pin S事件

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

A session waits for “cursor: pin S” when it wants a specific mutex in S (share) mode on a specific cursor and there is no concurrent X holder but it could not acquire that mutex immediately. This may seem a little strange as one might question why there should be any form of wait to get a mutex which has no session holding it in an incompatible mode. The reason for the wait is that in order to acquire the mutex in S mode (or release it) the session has to increment (or decrement) the mutex reference count and this requires an exclusive atomic update to the mutex structure itself. If there are concurrent sessions trying to make such an update to the mutex then only one session can actually increment (or decrement) the reference count at a time. A wait on “cursor: pin S” thus occurs if a session cannot make that atomic change immediately due to other concurrent requests.
Mutexes are local to the current instance in RAC environments.
Oracle10g中引用的mutexes机制一定程度的替代了library cache pin，其结构更简单，get&set的原子操作更快捷。
它相当于，每个child cursor下面都有一个mutexes这样的简单内存结构，当有session要执行该SQL而需要pin cursor操作的时候，session只需要以shared模式set这个内存位+1，表示session获得该mutex的shared mode lock.可以有很多session同时具有这个mutex的shared mode lock；但在同一时间，只能有一个session在操作这个mutext +1或者-1。+1 -1的操作是排它性的原子操作。如果因为session并行太多，而导致某个session在等待其他session的mutext +1/-1操作,则该session要等待cursor: pin S等待事件。
当看到系统有很多session等待cursor: pin S事件的时候，要么是CPU不够快，要么是某个SQL的并行执行次数太多了而导致在child cursor上的mutex操作争用。如果是Capacity的问题，则可以升级硬件。如果是因为SQL的并行太多，则要么想办法降低该SQL执行次数，要么将该SQL复制成N个其它的SQL。
select /*SQL 1*/object_name from t where object_id=?
select /*SQL 2*/object_name from t where object_id=?
select /*SQL …*/object_name from t where object_id=?
select /*SQL N*/object_name from t where object_id=?
这样就有了N个SQL Cursor,N个Mutex内存结构，就将争用分散开来，类似partition的作用了

Oracle DDL 并行(10G)

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：Oracle DDL 并行(10G)

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

1、CREATE INDEX 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR create index ind_t2 on t1(object_name) online nologging PARALLEL(degree 4);
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2130784087
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | CREATE INDEX STATEMENT   |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (ORDER)     | :TQ10001 |  Q1,01 | P->S | QC (ORDER) |
|   3 |    INDEX BUILD NON UNIQUE| IND_T2   |  Q1,01 | PCWP |            |
|   4 |     SORT CREATE INDEX    |          |  Q1,01 | PCWP |            |
|   5 |      PX RECEIVE          |          |  Q1,01 | PCWP |            |
|   6 |       PX SEND RANGE      | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE PARALLEL DDL;
Session altered.
SQL> EXPLAIN PLAN FOR create index ind_t2 on t1(object_name) online nologging PARALLEL(degree 4);
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2130784087
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | CREATE INDEX STATEMENT   |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (ORDER)     | :TQ10001 |  Q1,01 | P->S | QC (ORDER) |
|   3 |    INDEX BUILD NON UNIQUE| IND_T2   |  Q1,01 | PCWP |            |
|   4 |     SORT CREATE INDEX    |          |  Q1,01 | PCWP |            |
|   5 |      PX RECEIVE          |          |  Q1,01 | PCWP |            |
|   6 |       PX SEND RANGE      | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------

2、REBUILD INDEX 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR alter  index ind_t2 rebuild online nologging PARALLEL(degree 4);
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2130784087
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | ALTER INDEX STATEMENT    |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (ORDER)     | :TQ10001 |  Q1,01 | P->S | QC (ORDER) |
|   3 |    INDEX BUILD NON UNIQUE| IND_T2   |  Q1,01 | PCWP |            |
|   4 |     SORT CREATE INDEX    |          |  Q1,01 | PCWP |            |
|   5 |      PX RECEIVE          |          |  Q1,01 | PCWP |            |
|   6 |       PX SEND RANGE      | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE PARALLEL DDL;
Session altered.
SQL> EXPLAIN PLAN FOR alter  index ind_t2 rebuild online nologging PARALLEL(degree 4);
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2130784087
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | ALTER INDEX STATEMENT    |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (ORDER)     | :TQ10001 |  Q1,01 | P->S | QC (ORDER) |
|   3 |    INDEX BUILD NON UNIQUE| IND_T2   |  Q1,01 | PCWP |            |
|   4 |     SORT CREATE INDEX    |          |  Q1,01 | PCWP |            |
|   5 |      PX RECEIVE          |          |  Q1,01 | PCWP |            |
|   6 |       PX SEND RANGE      | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------

3、CREATE TABLE 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR create table t_6 parallel (degree 4)
  2    as select /*+ parallel (t1,4) */ * from t1 where rownum<5000000;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2102891290
------------------------------------------------------------------------------
| Id  | Operation                    | Name     |    TQ  |IN-OUT| PQ Distrib |
------------------------------------------------------------------------------
|   0 | CREATE TABLE STATEMENT       |          |        |      |            |
|   1 |  PX COORDINATOR              |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)        | :TQ20001 |  Q2,01 | P->S | QC (RAND)  |
|   3 |    LOAD AS SELECT            | T_6      |  Q2,01 | PCWP |            |
|   4 |     BUFFER SORT              |          |  Q2,01 | PCWC |            |
|   5 |      PX RECEIVE              |          |  Q2,01 | PCWP |            |
|   6 |       PX SEND ROUND-ROBIN    | :TQ20000 |        | S->P | RND-ROBIN  |
|   7 |        COUNT STOPKEY         |          |        |      |            |
|   8 |         PX COORDINATOR       |          |        |      |            |
|   9 |          PX SEND QC (RANDOM) | :TQ10000 |  Q1,00 | P->S | QC (RAND)  |
|  10 |           COUNT STOPKEY      |          |  Q1,00 | PCWC |            |
|  11 |            PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|  12 |             TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
------------------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE PARALLEL DDL;
Session altered.
SQL> EXPLAIN PLAN FOR create table t_6 parallel (degree 4)
  2    as select /*+ parallel (t1,4) */ * from t1 where rownum<5000000;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2102891290
------------------------------------------------------------------------------
| Id  | Operation                    | Name     |    TQ  |IN-OUT| PQ Distrib |
------------------------------------------------------------------------------
|   0 | CREATE TABLE STATEMENT       |          |        |      |            |
|   1 |  PX COORDINATOR              |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)        | :TQ20001 |  Q2,01 | P->S | QC (RAND)  |
|   3 |    LOAD AS SELECT            | T_6      |  Q2,01 | PCWP |            |
|   4 |     BUFFER SORT              |          |  Q2,01 | PCWC |            |
|   5 |      PX RECEIVE              |          |  Q2,01 | PCWP |            |
|   6 |       PX SEND ROUND-ROBIN    | :TQ20000 |        | S->P | RND-ROBIN  |
|   7 |        COUNT STOPKEY         |          |        |      |            |
|   8 |         PX COORDINATOR       |          |        |      |            |
|   9 |          PX SEND QC (RANDOM) | :TQ10000 |  Q1,00 | P->S | QC (RAND)  |
|  10 |           COUNT STOPKEY      |          |  Q1,00 | PCWC |            |
|  11 |            PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|  12 |             TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
------------------------------------------------------------------------------

4、说明
1）本次测试的数据库版本为10.2.0.4，Linux环境，其他版本可能有差异
2）关于INDEX的并行操作，并行度可能不会和指定相同（测试为2倍）
3）操作过程中，是否指定ddl 并发，效果相同。建议指定未佳：
ALTER SESSION ENABLE PARALLEL DDL;
ALTER SESSION DISABLE PARALLEL DDL;
4）修改表结构操作，指定并发无效（待寻找方法）

Oracle DML并行

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：Oracle DML并行

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

1、UPDATE 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR update /*+ parallel (t1,4) */ t1 set object_name='chengfei';
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 121765358
-----------------------------------------------------------------------
| Id  | Operation             | Name     |    TQ  |IN-OUT| PQ Distrib |
-----------------------------------------------------------------------
|   0 | UPDATE STATEMENT      |          |        |      |            |
|   1 |  UPDATE               | T1       |        |      |            |
|   2 |   PX COORDINATOR      |          |        |      |            |
|   3 |    PX SEND QC (RANDOM)| :TQ10000 |  Q1,00 | P->S | QC (RAND)  |
|   4 |     PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   5 |      TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE  PARALLEL DML;
Session altered.
SQL> EXPLAIN PLAN FOR update /*+ parallel (t1,4) */ t1 set object_name='chengfei';
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3308547044
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | UPDATE STATEMENT         |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)    | :TQ10001 |  Q1,01 | P->S | QC (RAND)  |
|   3 |    INDEX MAINTENANCE     | T1       |  Q1,01 | PCWP |            |
|   4 |     PX RECEIVE           |          |  Q1,01 | PCWP |            |
|   5 |      PX SEND RANGE       | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   6 |       UPDATE             | T1       |  Q1,00 | PCWP |            |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------

通过执行计划可以看出，只有执行了ALTER SESSION ENABLE PARALLEL DML后，UPDATE操作才真正的实现了并行操作，如果不执行该语句，只是执行了并发查询，并没有实现并发更新操作
2、DELETE 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR delete /*+ parallel (t1,3) */ from t1;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 3718066193
-----------------------------------------------------------------------
| Id  | Operation             | Name     |    TQ  |IN-OUT| PQ Distrib |
-----------------------------------------------------------------------
|   0 | DELETE STATEMENT      |          |        |      |            |
|   1 |  DELETE               | T1       |        |      |            |
|   2 |   PX COORDINATOR      |          |        |      |            |
|   3 |    PX SEND QC (RANDOM)| :TQ10000 |  Q1,00 | P->S | QC (RAND)  |
|   4 |     PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   5 |      TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
-----------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE  PARALLEL DML;
Session altered.
SQL> EXPLAIN PLAN FOR delete /*+ parallel (t1,3) */ from t1;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2132458150
--------------------------------------------------------------------------
| Id  | Operation                | Name     |    TQ  |IN-OUT| PQ Distrib |
--------------------------------------------------------------------------
|   0 | DELETE STATEMENT         |          |        |      |            |
|   1 |  PX COORDINATOR          |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)    | :TQ10001 |  Q1,01 | P->S | QC (RAND)  |
|   3 |    INDEX MAINTENANCE     | T1       |  Q1,01 | PCWP |            |
|   4 |     PX RECEIVE           |          |  Q1,01 | PCWP |            |
|   5 |      PX SEND RANGE       | :TQ10000 |  Q1,00 | P->P | RANGE      |
|   6 |       DELETE             | T1       |  Q1,00 | PCWP |            |
|   7 |        PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   8 |         TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
--------------------------------------------------------------------------

试验证明，也需要执行ALTER SESSION ENABLE PARALLEL DML，才能够实现真正的删除并发操作
3、INSERT 操作

SQL> conn chf/xifenfei
Connected.
SQL> EXPLAIN PLAN FOR INSERT  /*+ parallel (t_1,4) */ INTO t_1 SELECT /*+ parallel (t1,4) */* FROM t1;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2494645258
----------------------------------------------------------------------
| Id  | Operation            | Name     |    TQ  |IN-OUT| PQ Distrib |
----------------------------------------------------------------------
|   0 | INSERT STATEMENT     |          |        |      |            |
|   1 |  PX COORDINATOR      |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)| :TQ10000 |  Q1,00 | P->S | QC (RAND)  |
|   3 |    PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   4 |     TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
----------------------------------------------------------------------
SQL> conn chf/xifenfei
Connected.
SQL> ALTER SESSION ENABLE  PARALLEL DML;
Session altered.
SQL> EXPLAIN PLAN FOR INSERT  /*+ parallel (t_1,4) */ INTO t_1 SELECT /*+ parallel (t1,4) */* FROM t1;
Explained.
SQL> SELECT * FROM table (DBMS_XPLAN.display(NULL, NULL, 'BASIC +PARALLEL'));
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 783041698
-------------------------------------------------------------------------
| Id  | Operation               | Name     |    TQ  |IN-OUT| PQ Distrib |
-------------------------------------------------------------------------
|   0 | INSERT STATEMENT        |          |        |      |            |
|   1 |  PX COORDINATOR         |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)   | :TQ10001 |  Q1,01 | P->S | QC (RAND)  |
|   3 |    LOAD AS SELECT       | T_1      |  Q1,01 | PCWP |            |
|   4 |     PX RECEIVE          |          |  Q1,01 | PCWP |            |
|   5 |      PX SEND ROUND-ROBIN| :TQ10000 |  Q1,00 | P->P | RND-ROBIN  |
|   6 |       PX BLOCK ITERATOR |          |  Q1,00 | PCWC |            |
|   7 |        TABLE ACCESS FULL| T1       |  Q1,00 | PCWP |            |
-------------------------------------------------------------------------

通过这个执行计划可以发现，数据是被使用APPEND方式插入到表中，如果需要常规方式插入，需要加上noappend提示，同样设置了session 并行dml才能够实现真正意义上的插入并发操作
4、总结
通过上面的试验可以得出，如果要DML实现真正意义上的并发，在开始执行需要并发语句前，需要执行开启session并发
ALTER SESSION ENABLE PARALLEL DML;
在执行完语句后，需要执行关闭session并发
ALTER SESSION DISABLE PARALLEL DML;

Oracle直方图理解与实验

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标题：Oracle直方图理解与实验

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

一.Oracle中直方图的作用
直方图是一种对被管理对象某一方面质量进行管理的描述工具，那么在Oracle中自然它也是对Oracle中某个对象质量的描述工具，这个对象就是Oracle中最重要的东西——“数据”。
在Oracle中直方图是一种对数据分布质量情况进行描述的工具。它会按照某一列不同值出现数量多少，以及出现的频率高低来绘制数据的分布情况，以便能够指导优化器根据数据的分布做出正确的选择。在某些情况下，表的列中的数值分布将会影响优化器使用索引还是执行全表扫描的决策。当 where 子句的值具有不成比例数量的数值时，将出现这种情况，使得全表扫描比索引访问的成本更低。这种情况下如果where 子句的过滤谓词列之上上有一个合理的正确的直方图，将会对优化器做出正确的选择发挥巨大的作用，使得SQL语句执行成本最低从而提升性能。
二.Oracle中使用直方图的场合
在分析表或索引时，直方图用于记录数据的分布。通过获得该信息，基于成本的优 化器就可以决定使用将返回少量行的索引，而避免使用基于限制条件返回许多行的索引。直方图的使用不受索引的限制，可以在表的任何列上构建直方图。
构造直方图最主要的原因就是帮助优化器在表中数据严重偏斜时做出更好的规划：例如，如果一到两个值构成了表中的大部分数据(数据偏斜)，相关的索引就可能无法帮助减少满足查询所需的I/O数量。创建直方图可以让基于成本的优化器知道何时使用索引才最合适，或何时应该根据WHERE子句中的值返回表中80％的记录。
通常情况下在以下场合中建议使用直方图：
（1）、当Where子句引用了列值分布存在明显偏差的列时：当这种偏差相当明显时，以至于 WHERE 子句中的值将会使优化器选择不同的执行计划。这时应该使用直方图来帮助优化器来修正执行路径。（注意：如果查询不引用该列，则创建直方图没有意义。这种错误很常见，许多 DBA 会在偏差列上创建柱状图，即使没有任何查询引用该列。）
（2）、当列值导致不正确的判断时：这种情况通常会发生在多表连接时，例如，假设我们有一个五项的表联接，其结果集只有 10 行。Oracle 将会以一种使第一个联接的结果集（集合基数）尽可能小的方式将表联接起来。通过在中间结果集中携带更少的负载，查询将会运行得更快。为了使中间结果最小化，优化器尝试在 SQL 执行的分析阶段评估每个结果集的集合基数。在偏差的列上拥有直方图将会极大地帮助优化器作出正确的决策。如优化器对中间结果集的大小作出不正确的判断，它可能会选择一种未达到最优化的表联接方法。因此向该列添加直方图经常会向优化器提供使用最佳联接方法所需的信息。
三.Oracle直方图的种类
Oracle利用直方图来提高非均匀数据分布的选择率和技术的计算精度。但是实际上Oracle会采用另种不同的策略来生成直方图：其中一种是针对包含很少不同值的数据集；另一种是针对包含很多不同的数据集。Oracle会针对第一种情况生成频率直方图，针对第二种情况生成高度均衡直方图。通常情况下当BUCTET < 表的NUM_DISTINCT值得到的是HEIGHT BALANCED（高度平衡）直方图，而当BUCTET > 表的NUM_DISTINCT值的时候得到的是FREQUENCY（频率）直方图
四、试验证明（有直方图执行计划更加准确）

SQL> create table t_xff
  2  as select * from dba_objects;
Table created
SQL> create index ind_t_xff on t_xff(object_id) online nologging;
Index created
SQL> SELECT MAX(object_id),MIN(object_id) FROM t_xff;
MAX(OBJECT_ID) MIN(OBJECT_ID)
-------------- --------------
         76800              2
SQL>  UPDATE t_xff SET object_id=1000 WHERE object_id>100 AND object_id<76000;
72965 rows updated
SQL> commit;
Commit complete
SQL>
SQL>   BEGIN
  2      DBMS_stats.gather_table_stats(cascade => TRUE,degree => 2
  3      ,estimate_percent => 100,force => TRUE,ownname => USER,tabname => 'T_XFF');
  4   END;
  5  /
PL/SQL procedure successfully completed
SQL> SELECT * FROM user_histograms WHERE table_name='T_XFF' AND column_name='OBJECT_ID';
TABLE COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE ENDPOINT_A
----- ---------- --------------- -------------- ----------
T_XFF OBJECT_ID            1          2
T_XFF OBJECT_ID            2          3
……
T_XFF OBJECT_ID            73205          76789
T_XFF OBJECT_ID            73206          76800
SQL>   SELECT COLUMN_NAME,HISTOGRAM FROM USER_TAB_COLS WHERE TABLE_NAME='T_XFF' AND column_name='OBJECT_ID';
COLUMN_NAME                    HISTOGRAM
------------------------------ ---------------
OBJECT_ID                      FREQUENCY
--在gather_table_stats方法中，默认的method_opt值为：FOR ALL COLUMNS SIZE AUTO，所以也是会收集直方图的统计信息（和oracle版本相关）
--注意：ENDPOINT_NUMBER ，ENDPOINT_VALUE 的分布情况
SQL> set autot trace exp stat
SQL> select object_name from t_xff where object_id=100;
执行计划
----------------------------------------------------------
Plan hash value: 2950241517
--------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |     1 |    29 |     2   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T_XFF     |     1 |    29 |     2   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_T_XFF |     1 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"=100)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        432  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> select object_name from t_xff where object_id=1000;
已选择72965行。
执行计划
----------------------------------------------------------
Plan hash value: 667573674
---------------------------------------------------------------------------
| Id  | Operation         | Name  | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |       | 72965 |  2066K|   292   (1)| 00:00:04 |
|*  1 |  TABLE ACCESS FULL| T_XFF | 72965 |  2066K|   292   (1)| 00:00:04 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   1 - filter("OBJECT_ID"=1000)
统计信息
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       5833  consistent gets
         16  physical reads
          0  redo size
    2487154  bytes sent via SQL*Net to client
      53920  bytes received via SQL*Net from client
       4866  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      72965  rows processed
--观察发现，因为有直方图的存在，oracle会只能的选择使用index或者全表扫描
SQL>   BEGIN
  2      DBMS_stats.gather_table_stats(cascade => TRUE,degree => 2
  3      ,estimate_percent => 100,force => TRUE,ownname => USER,tabname => 'T_XFF',method_opt => 'FOR ALL COLUMNS SIZE 1');
  4   END;
  5  /
PL/SQL procedure successfully completed
--删除直方图，设置method_opt：FOR ALL COLUMNS SIZE 1即可
SQL>  SELECT * FROM user_histograms WHERE table_name='T_XFF' AND column_name='OBJECT_ID';
TABLE COLUMN_NAM ENDPOINT_NUMBER ENDPOINT_VALUE ENDPOINT_A
----- ---------- --------------- -------------- ----------
T_XFF OBJECT_ID                0              2
T_XFF OBJECT_ID                1          76800
SQL> SELECT COLUMN_NAME,HISTOGRAM FROM USER_TAB_COLS WHERE TABLE_NAME='T_XFF' AND column_name='OBJECT_ID';
COLUMN_NAME                    HISTOGRAM
------------------------------ ---------------
OBJECT_ID                      NONE
SQL> select object_name from t_xff where object_id=100;
执行计划
----------------------------------------------------------
Plan hash value: 2950241517
--------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |   303 |  8787 |     7   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T_XFF     |   303 |  8787 |     7   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_T_XFF |   303 |       |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"=100)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        432  bytes sent via SQL*Net to client
        415  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL> select object_name from t_xff where object_id=1000;
已选择72965行。
执行计划
----------------------------------------------------------
Plan hash value: 2950241517
--------------------------------------------------------------------------------
| Id  | Operation                   | Name      | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |           |   303 |  8787 |     7   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| T_XFF     |   303 |  8787 |     7   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN          | IND_T_XFF |   303 |       |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("OBJECT_ID"=1000)
统计信息
----------------------------------------------------------
          0  recursive calls
          0  db block gets
       5833  consistent gets
          0  physical reads
          0  redo size
    2487154  bytes sent via SQL*Net to client
      53919  bytes received via SQL*Net from client
       4866  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      72965  rows processed
--没有了直方图，oracle傻瓜的选择也使用index
--虽然两次逻辑读一样，但是全表扫描涉及到一次可以读多块，但是index扫描一次只能读一个数据块

DBMS_STATS比较复杂参数

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标题：DBMS_STATS比较复杂参数

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

method_opt
Accepts:
FOR ALL [INDEXED | HIDDEN] COLUMNS [size_clause]
FOR COLUMNS [size clause] column|attribute [size_clause] [,column|attribute [size_clause]…]
size_clause is defined as size_clause := SIZE {integer | REPEAT | AUTO | SKEWONLY}
– integer : Number of histogram buckets. Must be in the range [1,254].
– REPEAT : Collects histograms only on the columns that already have histograms.
– AUTO : Oracle determines the columns to collect histograms based on data distribution and the workload of the columns.
– SKEWONLY : Oracle determines the columns to collect histograms based on the data distribution of the columns.
举例说明：
method_opt => ‘FOR COLUMNS size 254 object_id’ 收集objct_id列直方图
method_opt => ‘FOR COLUMNS size 1 object_id’ 删除object_id列直方图
method_opt => ‘for all columns size repeat’ 重新分析现有直方图
method_opt => ‘for all columns size auto’ oracle决定收集哪些列的直方图（需要设置table monitoring）
method_opt => ‘for all columns size skewonly’ oracle分析所有列的分布情况，生成直方图
method_opt => ‘FOR COLUMNS object_id size SKEWONLY’ 收集object_id列分布情况，生成直方图
method_opt => ‘FOR all INDEXED COLUMNS size SKEWONLY’ 收集index列分布情况，并生成直方图
granularity
Granularity of statistics to collect (only pertinent if the table is partitioned).
‘ALL’ – gathers all (subpartition, partition, and global) statistics
‘AUTO’- determines the granularity based on the partitioning type. This is the default value.
‘DEFAULT’ – gathers global and partition-level statistics. This option is obsolete, and while currently supported, it is included in the documentation for legacy reasons only. You should use the ‘GLOBAL AND PARTITION’ for this functionality. Note that the default value is now ‘AUTO’.
‘GLOBAL’ – gathers global statistics
‘GLOBAL AND PARTITION’ – gathers the global and partition level statistics. No subpartition level statistics are gathered even if it is a composite partitioned object.
‘PARTITION ‘- gathers partition-level statistics
‘SUBPARTITION’ – gathers subpartition-level statistics.
options
Further specification of which objects to gather statistics for:
GATHER: Gathers statistics on all objects in the schema.
GATHER AUTO: Gathers all necessary statistics automatically. Oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. When GATHER AUTO is specified, the only additional valid parameters are ownname, stattab, statid, objlist and statown; all other parameter settings are ignored. Returns a list of processed objects.
GATHER STALE: Gathers statistics on stale objects as determined by looking at the *_tab_modifications views. Also, return a list of objects found to be stale.
GATHER EMPTY: Gathers statistics on objects which currently have no statistics. also, return a list of objects found to have no statistics.
LIST AUTO: Returns a list of objects to be processed with GATHER AUTO.
LIST STALE: Returns list of stale objects as determined by looking at the *_tab_modifications views.
LIST EMPTY: Returns list of objects which currently have no statistics.

BITMAP CONVERSION FROM ROWIDS

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标题：BITMAP CONVERSION FROM ROWIDS

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

在有些执行计划中，可以会看到 BITMAP CONVERSION FROM ROWIDS这样的东东，也许你会感觉奇怪，我没有使用位图索引怎么出现了bitmap。
我通过一个sql和大家分析下原因：
sql语句为：

SELECT *
  FROM (SELECT a.*, ROWNUM rn
          FROM (  SELECT module_no, MAX (id) AS id
                    FROM vasoa.tab_moa_historypage t
                   WHERE t.company_id = :1 AND t.user_id = :2 AND t.TYPE = :3
                GROUP BY module_no
                ORDER BY id DESC) a
         WHERE ROWNUM <= :4) b
WHERE b.rn >= :5

执行计划为：

表结构为：

目前索引情况：

通过观察执行计划的图片可以发现，使用了 BITMAP CONVERSION FROM ROWIDS，其目的是：.oracle将btree索引中获得的rowid信息通过BITMAP CONVERSION FROM ROWIDS的步骤转换成bitmap进行匹配,然后匹配完成后通过BITMAP CONVERSION TO ROWIDS再转换出rowid获得数据或者回表获得数据。这种想象出现的原因为：oracle的cbo是根据cost来决定大小来选择合适的执行计划，当它计算获得通过bitmap的方式执行的时候cost会更小，它就会选择使用这样的执行计划。一般出现这样的情况，都是因为对表建立的不适当的index导致，特别是对表中的唯一度不高的列建立了index，然后oracle就有可能选择两个这样的列转为为bitmap来执行。根据oracle的执行计划，肯定是cost最小的，但是它很多时候忽略了一致性读等其他条件，导致这个执行计划并非像oracle想象的那样最优，因为把btree index转为为bitmap index执行，需要消耗更多的cpu，特别是在cpu比较紧张的系统中，所以这样的情况如果发生在oltp系统中，一般都需要解决。
本例的解决办法是删除唯一度低的index，建立组合index。分别删除COMPANY_ID与USER_ID上的index，建立COMPANY_ID和USER_ID的组合index，执行计划如下：

V$LOCK视图相关知识

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标题：V$LOCK视图相关知识

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

1、V$LOCK视图结构

列名 类型 字段说明
ADDR RAW（4 | 8） Address of lock state object
KADDR RAW（4|8） Address of lock
SID NUMBER 会话的sid，可以和v$session 关联
TYPE VARCHAR2(2) 区分该锁保护对象的类型（表4）
TM – DML enqueue
TX – Transaction enqueue
UL – User supplied
–我们主要关注TX和TM两种类型的锁
–UL锁用户自己定义的，一般很少会定义，基本不用关注
–其它均为系统锁，会很快自动释放，不用关注
ID1
ID2		 NUMBER ID1,ID2的取值含义根据type的取值而有所不同
对于TM 锁
ID1表示被锁定表的object_id 可以和dba_objects视图关联取得具体表信息，ID2 值为0
对于TX 锁
ID1以十进制数值表示该事务所占用的回滚段号和事务槽slot number号,其组形式:
0xRRRRSSSS,RRRR=RBS/UNDO NUMBER,SSSS=SLOT NUMBER
ID2 以十进制数值表示环绕wrap的次数，即事务槽被重用的次数
LMODE NUMBER
  • 0 – none
  • 1 – null (NULL)
  • 2 – row-S (SS)
  • 3 – row-X (SX)
  • 4 – share (S)
  • 5 – S/Row-X (SSX)
  • 6 – exclusive (X)
  • 具体见表3
REQUEST NUMBER 同LMODE
–大于0时，表示当前会话被阻塞，其它会话占有改锁的模式
CTIME NUMBER
  • 已持有或者等待锁的时间
BLOCK NUMBER
  • 是否阻塞其他会话锁申请 1:阻塞 0:不阻塞


2、其它相关视图说明

视图名 描述 主要字段说明
v$session 查询会话的信息和锁的信息。 sid,serial#：表示会话信息。
program：表示会话的应用程序信息。
row_wait_obj#：表示等待的对象,和dba_objects中的object_id相对应。
lockwait :该会话等待的锁的地址,与v$lock的kaddr对应.
v$session_wait 查询等待的会话信息。 sid：表示持有锁的会话信息。
Seconds_in_wait：表示等待持续的时间信息
Event：表示会话等待的事件，锁等于enqueue
dba_locks 对v$lock的格式化视图。 Session_id：和v$lock中的Sid对应。
Lock_type：和v$lock中的type对应。
Lock_ID1： 和v$lock中的ID1对应。
Mode_held,mode_requested：和v$lock中的lmode,request相对应。
v$locked_object 只包含DML的锁信息，包括回滚段和会话信息。 Xidusn,xidslot,xidsqn：表示回滚段信息。和v$transaction相关联。
Object_id：表示被锁对象标识。
Session_id：表示持有锁的会话信息。
Locked_mode：表示会话等待的锁模式的信息，和v$lock中的lmode一致。

表3

锁模式 锁描述 解释 SQL操作
0 none
1 NULL 空 Select
2 SS(Row-S) 行级共享锁，其他对象只能查询这些数据行 Select for update
Lock for update
Lock row share
3 SX(Row-X) 行级排它锁,在提交前不允许做DML操作 Insert/update/Delete
Lock row share
4 S(Share) 共享锁 Create index
Lock share
5 SSX(S/Row-X) 共享行级排它锁 Lock share row exclusive
6 X(Exclusive) 排它锁 Alter table
Drop able
Drop index
Truncate table
Lock exclusive

表4

System Type Description System Type Description
BL Buffer hash table instance NA..NZ Library cache pin instance (A..Z = namespace)
CF Control file schema global enqueue PF Password File
CI Cross-instance function invocation instance PI, PS Parallel operation
CU Cursor bind PR Process startup
DF datafile instance QA..QZ Row cache instance (A..Z = cache)
DL Direct loader parallel index create RT Redo thread global enqueue
DM Mount/startup db primary/secondary instance SC System change number instance
DR Distributed recovery process SM SMON
DX Distributed transaction entry SN Sequence number instance
FS File set SQ Sequence number enqueue
HW Space management operations on a specific segment SS Sort segment
IN Instance number ST Space transaction enqueue
IR Instance recovery serialization global enqueue SV Sequence number value
IS Instance state TA Generic enqueue
IV Library cache invalidation instance TS Temporary segment enqueue (ID2=0)
JQ Job queue TS New block allocation enqueue (ID2=1)
KK Thread kick TT Temporary table enqueue
LA .. LP Library cache lock instance lock (A..P = namespace) UN User name
MM Mount definition global enqueue US Undo segment DDL
MR Media recovery WL Being-written redo log instance

select max(id),min(id) from table优化

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：select max(id),min(id) from table优化

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

1、查看数据库版本
SQL> select * from v$version where rownum<2; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production 2、创建表和索引
create table t_a as select * from dba_objects;
create index t_a_ind on t_a(object_id);
3、查询最大值
SQL> select max(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 3226265922
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | | |
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
431 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
4、查询最小值
SQL> select min(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 3226265922
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | 13 | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | |
|
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
2 consistent gets
0 physical reads
0 redo size
429 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
5、查询最大值和最小值
SQL> select max(object_id),min(object_id) from t_a;
执行计划
———————————————————-
Plan hash value: 2127980459
—————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————
| 0 | SELECT STATEMENT | | 1 | 13 | 293 (1)| 00:00:04 |
| 1 | SORT AGGREGATE | | 1 | 13 | | |
| 2 | TABLE ACCESS FULL| T_A | 78093 | 991K| 293 (1)| 00:00:04 |
—————————————————————————
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
4 recursive calls
0 db block gets
1119 consistent gets
1044 physical reads
0 redo size
502 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
6、查询最大值和最小值（排除null）
SQL> select max(object_id),min(object_id) from t_a where object_id is not null;
执行计划
———————————————————-
Plan hash value: 1214261695
———————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time
|
———————————————————————————
| 0 | SELECT STATEMENT | | 1 | 13 | 50 (2)| 00:00:01
|
| 1 | SORT AGGREGATE | | 1 | 13 | |
|
|* 2 | INDEX FAST FULL SCAN| T_A_IND | 78093 | 991K| 50 (2)| 00:00:01
|
———————————————————————————
Predicate Information (identified by operation id):
—————————————————
2 – filter(“OBJECT_ID” IS NOT NULL)
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
4 recursive calls
0 db block gets
242 consistent gets
0 physical reads
0 redo size
502 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
7、分别查询最大值和最小值
SQL> select (select max(object_id) from t_a) max,(select min(object_id) from t_a) min from dual;
执行计划
———————————————————-
Plan hash value: 312201770
————————————————————————————–
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
————————————————————————————–
| 0 | SELECT STATEMENT | | 1 | | 2 (0)| 00:00:01 |
| 1 | SORT AGGREGATE | | 1 | 13 | |
| 2 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
| 3 | SORT AGGREGATE | | 1 | 13 | |
| 4 | INDEX FULL SCAN (MIN/MAX)| T_A_IND | 1 | 13 | 2 (0)| 00:00:01 |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
————————————————————————————–
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
480 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
说明：
1、单查询最大值或者最小值，sql会自动走index
2、如果同时查询最大值和最小值，sql会使用全表扫描，而不是我们想象的索引快速扫描
3、加上where 排除掉null的情况，sql使用索引快速扫描，原因是：在不能确定索引列不为null（或者没有排除掉null）的情况下，不会使用索引快速扫描，而sql为了保证正确而采用了全表扫描
4、INDEX FULL SCAN (MIN/MAX)扫描效率很搞，所以把最大值，最小值分开查询，提高执行效率
5、其他写法
SQL> select (select /*+ index_asc(t_a t_a_ind) */ object_id from t_a where rownu
m=1) min ,(select /*+ index_desc(t_a t_a_ind) */ object_id from t_a where rownum=1)
max from dual;
执行计划
———————————————————-
Plan hash value: 674626822
—————————————————————————————
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
—————————————————————————————
| 0 | SELECT STATEMENT | | 1 | | 2 (0)| 00:
00:01 |
|* 1 | COUNT STOPKEY | | | | | |
| 2 | INDEX FULL SCAN | T_A_IND | 78093 | 991K| 2 (0)| 00:
00:01 |
|* 3 | COUNT STOPKEY | | | | |
| 4 | INDEX FULL SCAN DESCENDING| T_A_IND | 78093 | 991K| 2 (0)| 00:
00:01 |
| 5 | FAST DUAL | | 1 | | 2 (0)| 00:00:01 |
—————————————————————————————
Predicate Information (identified by operation id):
—————————————————
1 – filter(ROWNUM=1)
3 – filter(ROWNUM=1)
Note—— dynamic sampling used for this statement (level=2)
统计信息
———————————————————-
0 recursive calls
0 db block gets
4 consistent gets
0 physical reads
0 redo size
480 bytes sent via SQL*Net to client
416 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed
注意：
1）这个要正确执行，需要一个前提条件object_id这列要为not null限制条件，不然会hint提示无效
2）从执行计划的统计信息上看，这个和INDEX FULL SCAN (MIN/MAX)方式的执行效率一样

statspack安装

联系：手机/微信(+86 17813235971) QQ(107644445)

标题：statspack安装

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

今天发现关于statspack的安装没有记录下来，现在记录下，下次需要用的时候直接查找blog，而不用在硬盘中查找相关安装配置文件
1、创建statspack专用表空间
CREATE TABLESPACE SP
DATAFILE
‘/opt/oracle/oradata/usercent/PS_1.001.dbf’ SIZE 10M AUTOEXTEND ON NEXT 10M MAXSIZE 5G,
‘/opt/oracle/oradata/usercent/PS_1.002.dbf’ SIZE 10M AUTOEXTEND ON NEXT 10M MAXSIZE 5G,
‘/opt/oracle/oradata/usercent/PS_1.003.dbf’ SIZE 10M AUTOEXTEND ON NEXT 10M MAXSIZE 5G
LOGGING
PERMANENT
EXTENT MANAGEMENT LOCAL AUTOALLOCATE
BLOCKSIZE 8K
SEGMENT SPACE MANAGEMENT AUTO;
2、检测系统中是否有PERFSTAT用户
如果有，需要查询所跑的业务，做一些处理，然后删除
select * from dba_users where username=’PERFSTAT’;
drop user PERFSTAT cascade;
3、检查job_queue_processes
SQL> show parameter job
NAME TYPE VALUE
———————————— ———– ——————————
job_queue_processes integer 6
如果为0，请使用
alter system set job_queue_processes=6;
进行修改，当然数值不一定是6
4、检查timed_statistics
SQL> show parameter timed_statistics
NAME TYPE VALUE
———————————— ———– ——————————
timed_statistics boolean TRUE
如果timed_statistics为false，请使用下面命令修改为true
alter system set timed_statistics=true;
4、安装statspack
4.1）使用sys用户登录数据库
4.2）安装statspack主体程序
执行@?/rdbms/admin/spcreate.sql
如果失败，请执行@?/rdbms/admin/spdrop.sql，然后重新安装
4.3）设置自动采集信息
执行@?/rdbms/admin/spauto.sql
可以通过vi修改采集时间频率