DROP_SNAPSHOT_RANGE过程不能清理表RM$_SNAPSHOT

今天在测试、验证DROP_SNAPSHOT_RANGE不能彻底快照的过程中遇到了DROP_SNAPSHOT_RANGE无法清理WRM$_SNAPSHOT_DETAILS表中数据的情况，测试服务器版本为10.2.0.4.0，AWR的快照是1小时采集一次数据，快照保留14天，也就是二周。具体情况如下所示：

SQL> select * from v$version;

BANNER

----------------------------------------------------------------

Oracle Database 10g Release 10.2.0.4.0 - 64bit Production

PL/SQL Release 10.2.0.4.0 - Production

CORE    10.2.0.4.0      Production

TNS for Linux: Version 10.2.0.4.0 - Production

NLSRTL Version 10.2.0.4.0 - Production

SQL> COL SNAP_INTERVAL FOR A20;

SQL> COL TETENTION FOR A26;

SQL> SELECT * FROM dba_hist_wr_control;

      DBID SNAP_INTERVAL        RETENTION             TOPNSQL

---------- -------------------- -------------------- ----------

3990839260 +00000 01:00:00.0    +00014 00:00:00.0     DEFAULT

SQL> SELECT MIN(SNAP_ID), MAX(SNAP_ID) FROM dba_hist_snapshot;

MIN(SNAP_ID) MAX(SNAP_ID)

------------ ------------

        7417        59195

SQL>

SQL>  SELECT MIN(SNAP_ID), MAX(SNAP_ID) FROM dba_hist_snapshot;

MIN(SNAP_ID) MAX(SNAP_ID)

------------ ------------

        7417        59196

SQL> select dbid, status, count(*)

  2  from wrm$_snapshot

  3  group by dbid, status;

      DBID     STATUS   COUNT(*)

---------- ---------- ----------

3990839260          0       1250

SQL> select min(snap_id), max(snap_id), dbid from wrm$_snapshot

  2  group by dbid;

MIN(SNAP_ID) MAX(SNAP_ID)       DBID

------------ ------------ ----------

        7417        59196 3990839260

SQL> exec dbms_workload_repository.drop_snapshot_range(7417,59196,3990839260);


PL/SQL procedure successfully completed.

SQL>  select min(snap_id), max(snap_id), dbid from wrm$_snapshot

  2  group by dbid;

MIN(SNAP_ID) MAX(SNAP_ID)       DBID

------------ ------------ ----------

        7417        59197 3990839260

SQL> select min(snap_id), max(snap_id), dbid from wrm$_snapshot

  2  group by dbid;

MIN(SNAP_ID) MAX(SNAP_ID)       DBID

------------ ------------ ----------

        7417        59197 3990839260

SQL> SELECT MIN(SNAP_ID), MAX(SNAP_ID) FROM dba_hist_snapshot;

MIN(SNAP_ID) MAX(SNAP_ID)

------------ ------------

        7417        59197

如上实验所示，DROP_SNAPSHOT_RANGE不能清理WRM$_SNAPSHOT_DETAILS中的数据，当然对于的空间就不会释放，另外，有些版本中Oracle仅仅修改了对应SNAPSHOT的状态，而并没有删除快照。PS:有些人可能被上面又是DBA_HIST_SNAPSHOT，又是WRM$_SNAPSHOT_DETAILS弄得有点晕，其实DBA_HIST_SNAPSHOT是视图,它的数据来源于表WRM$_SNAPSHOT_DETAILS，使用下面SQL就能查看具体定义

SELECT OWNER, VIEW_NAME, TEXT FROM DBA_VIEWS WHERE VIEW_NAME='DBA_HIST_SNAPSHOT';

"select snap_id, dbid, instance_number, startup_time,

       begin_interval_time, end_interval_time,

       flush_elapsed, snap_level, error_count

from WRM$_SNAPSHOT

where status = 0"

-------------------------------------------------------------分割线------------------------------------------------------

本来这篇文章写了好几天了，后面讨论发现其实有时候AWR快照不能删除，并不一定就是bug，也有可能是设置了AWR的基线，下面我来演示一下

SQL> select baseline_name, start_snap_id, end_snap_id

  2  from  dba_hist_baseline

  3  order by 1;

BASELINE_NAME            START_SNAP_ID END_SNAP_ID

------------------------ ------------- -----------

20100526                          7455        7464

20100602                          7624        7632

20100609                          7791        7800

20100616                          7959        7968

20100623                          8126        8135

20100630                          8294        8303

20100707                          8453        8477

20100714                          8621        8645

20100721                          8789        8813

20100728                          8957        8981

20100804                          9125        9149

BASELINE_NAME            START_SNAP_ID END_SNAP_ID

------------------------ ------------- -----------

20100811                          9293        9317

20100818                          9461        9485

20100825                          9620        9644

20100901                          9788        9812

20100908                          9957        9980

20100915                         10124       10148

20100922                         10292       10316

20100929                         10460       10484

20101006                         10628       10652

20101013                         10796       10820

20101020                         10964       10988

BASELINE_NAME            START_SNAP_ID END_SNAP_ID

------------------------ ------------- -----------

20101027                         11132       11156

20101103                         11300       11324

20101110                         11468       11492

20101117                         11636       11660

20101124                         11804       11828

20101201                         11972       11996

20101208                         12140       12164

20101215                         12308       12332

20101222                         12476       12500

20101229                         12644       12668

20110105                         12812       12836

BASELINE_NAME            START_SNAP_ID END_SNAP_ID

------------------------ ------------- -----------

20110112                         12980       13004

20110119                         13148       13172

20110126                         13316       13340

20110202                         13484       13508

SQL> SELECT MIN(SNAP_ID), MAX(SNAP_ID) FROM dba_hist_snapshot;

MIN(SNAP_ID) MAX(SNAP_ID)

------------ ------------

        7100        61252

SQL>  exec dbms_workload_repository.drop_snapshot_range(7100,7108,2179993557);

PL/SQL procedure successfully completed.

SQL> SELECT MIN(SNAP_ID), MAX(SNAP_ID) FROM dba_hist_snapshot;

MIN(SNAP_ID) MAX(SNAP_ID)

------------ ------------

        7287        61252

SQL> exec dbms_workload_repository.drop_snapshot_range(7455,7458,2179993557);

PL/SQL procedure successfully completed.

SQL>  SELECT SNAP_ID,STARTUP_TIME FROM dba_hist_snapshot

  2   WHERE SNAP_ID BETWEEN 7455 AND 7458;

   SNAP_ID STARTUP_TIME

---------- ---------------------------------------------------------------------------

      7455 16-JAN-10 12.18.46.000 PM

      7456 16-JAN-10 12.18.46.000 PM

      7457 16-JAN-10 12.18.46.000 PM

      7458 16-JAN-10 12.18.46.000 PM

SQL>

AWR快照SNAP_ID从7455 到7458 删除不掉，其实是因为这个段的快照设置成了基线，如下截图所示，所以，如果你发现快照删除不了的话，最好先检查这个SNAP_ID段是否设置成了基线。

另外还有就是有可能一个Bug引起的，这个只出现在特定版本中，官方文档WRM$_SNAPSHOT_DETAILS Table is Not Purged (文档 ID 1489801.1) 和文档 Document 9797851.8 Bug 9797851 - WRM$_SNAPHOST_DETAILS is never purged 都有描述这个Bug

APPLIES TO:

Oracle Database - Enterprise Edition - Version 11.2.0.3 to 12.1.0.1 [Release 11.2 to 12.1]
Information in this document applies to any platform.

SYMPTOMS

The following symptoms are observed:

AWR purge code is not automatically purging WRM$_SNAPSHOT_DETAILS, as expected
Even after dropping a range of snap id's using dbms_workload_repository.drop_snapshot_range(), the table is not purged.
Table WRM$_SNAPSHOT_DETAILS grows indefinitely.
There are many orphaned entries in the table WRM$_SNAPSHOT_DETAILS.

The number of orphaned rows for the table WRM$_SNAPSHOT_DETAILS can be found by running the following sql:

SQL> SELECT MIN(snap_id),

  max(snap_id) ,

  cast(min(begin_time) as date) "Min Begin Time",

  CAST(MAX(begin_time) AS  DATE) "Max Begin Time",

  COUNT(*)

FROM sys.wrm$_snapshot_details a

WHERE NOT EXISTS

  (SELECT *

  FROM sys.wrm$_snapshot b

  WHERE b.snap_id       = a.snap_id

  AND a.dbid            = b.dbid

  and a.instance_number = b.instance_number

  )

MIN(SNAP_ID) MAX(SNAP_ID) Min Begin Time       Max Begin Time         COUNT(*)

------------ ------------ -------------------- -------------------- ----------

           1         6993 29-nov-2011 21:00:01 24-sep-2012 22:00:17     577574

CAUSE

This issue is caused by an unpublished bug:

Document 9797851.8 Bug 9797851 - WRM$_SNAPHOST_DETAILS is never purged

The verification criteria for the bug are:

Drop a range of snap id's using dbms_workload_repository.drop_snapshot_range()
Check the corresponding snap id's in WRM$_SNAPSHOT_DETAILS.
If snap id's from the range that you chose to drop are still present, then you are hitting this bug.

SOLUTION

The following solutions are available:

The Patch 9797851 for unpublished Bug 9797851 is available for some platforms and can be downloaded from My Oracle Support
If the patch is not available on your platform on a supported version, please contact Oracle Support.
This issue will be fixed from release Oracle 12.1

As a workaround, it is possible to manually purge the range of snap id's from the table WRM$_SNAPSHOT_DETAILS using appropriate delete statments under the guidance of Oracle Support.

Note:

在下面版本中，这些bug才fix掉了，请留意自己的版本信息。