今天在測試、驗證DROP_SNAPSHOT_RANGE不能徹底快照的過程中遇到了DROP_SNAPSHOT_RANGE無法清理WRM$_SNAPSHOT_DETAILS表中數據的情況，測試服務器版本為10.2.0.5.0，AWR的快照是1小時采集一次數據，快照保留14天，也就是二周。具體情況如下所示：
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Release 10.2.0.5.0 - 64bit Production
PL/SQL Release 10.2.0.5.0 - Production
CORE 10.2.0.5.0 Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - 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
如上實驗所示，DROP_SNAPSHOT_RANGE不能清理WRM$_SNAPSHOT_DETAILS中的數據，當然對於的空間就不會釋放，另外，有些版本中Oracle僅僅修改了對應SNAPSHOT的狀態，而並沒有刪除快照。PS:有些人可能被上面又是DBA_HIST_SNAPSHOT，又是WRM$_SNAPSHOT_DETAILS弄得有點暈，其實DBA_HIST_SNAPSHOT是視圖,它的數據來源於表WRM$_SNAPSHOT_DETAILS，使用下面SQL就能查看具體定義
SELECT OWNER, VIEW_NAME, TEXT FROM DBA_VIEWS WHERE VIEW_NAME='DBA_HIST_SNAPSHOT';
"select snap_id, dbid, instance_number, startup_time,
begin_interval_time, end_interval_time,
flush_elapsed, snap_level, error_count
from WRM$_SNAPSHOT
where status = 0"
其實這個是一個Bug引起的，官方文檔WRM$_SNAPSHOT_DETAILS Table is Not Purged (文檔 ID 1489801.1) 和文檔 Document 9797851.8 Bug 9797851 - WRM$_SNAPHOST_DETAILS is never purged 都有描述這個Bug
The following symptoms are observed:
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$_snapshot b
WHERE b.snap_id = a.snap_id
AND a.dbid = b.dbid
and a.instance_number = b.instance_number
)
MIN(SNAP_ID) MAX(SNAP_ID) Min Begin Time Max Begin Time COUNT(*)
------------ ------------ -------------------- -------------------- ----------
1 6993 29-nov-2011 21:00:01 24-sep-2012 22:00:17 577574
This issue is caused by an unpublished bug:
Document 9797851.8 Bug 9797851 - WRM$_SNAPHOST_DETAILS is never purgedThe verification criteria for the bug are:
The following solutions are available:
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，這些bug才fix掉了，請留意自己的版本信息。
