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$_SNAPSHOT_DETAILS表中数据的情况，测试服务器版本为10.2.0.4.0，AWR的快照是1小时采集一次数据，快照保留14天，也就是二周。具体情况如下所示：
PL/SQL procedure successfully completed.
<a href="http://images2015.cnblogs.com/blog/73542/201607/73542-20160722103801794-1713507451.png"></a>
如上实验所示，DROP_SNAPSHOT_RANGE不能清理WRM$_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';
-------------------------------------------------------------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
<a href="http://images2015.cnblogs.com/blog/73542/201607/73542-20160722103802732-649354079.png"></a>
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。
<a href="http://images2015.cnblogs.com/blog/73542/201607/73542-20160722103803576-547869485.png"></a>
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
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.
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:
This issue is caused by an unpublished bug:
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$_SNAPSHOT_DETAILS.
If snap id's from the range that you chose to drop are still present, then you are hitting this bug.
The following solutions are available:
If the patch is not available on your platform on a supported version, please contact Oracle Support.
This issue will be fixed from release Oracle 12.1
As a workaround, it is possible to manually purge the range of snap id's from the table WRM$_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。
