block change tracking buffer space

Wait is related to the sizing / usage of the CTWR dba buffer in the Large Pool memory structure more

 

 

 

Solutions

Problem: When a session waits on the “Block Change Tracking Buffer” event, it indicates that there was a wait for space in the CTRW dba buffer. If this happens too often the performance of Backups and/or the entire database can suffer. There are several alternatives to fixing this if it occurs in your system.

 

Solution 1: Review the location of the change-tracking file to ensure that it’s not co-located on disks with other heavily used or “HOT” files. For example, do not locate the change-tracking file on the same disk with your redo or archive files.

 

Solution 2: Consider changing the value of Large_pool_size or the hidden parameter _bct_public_dba_buffer_size to a larger value. NOTE: Always check with Oracle Support before using a hidden parameter value as Oracle may not support these types of changes ( _bct_public_dba_buffer_size = total size of all public change tracking dba buffers).

 

Solution 3: Turn off the BCT feature so that it does not require the CTWR dba buffer.

 

Expanded Definition

When data blocks change, shadow processes track the changed blocks in a private area of memory at the same time they generate redo. When a commit is issued, the BCT information is copied to a shared area in Large Pool called ‘CTWR dba buffer’. At the checkpoint, a new background process, Change Tracking Writer (CTWR), writes the information from the buffer to the change-tracking file. If contention for space in the CTWR dba buffer occurs, a wait event called, ‘Block Change Tracking Buffer Space’ is recorded. By default, the CTWR process is disabled because it can introduce some minimal performance overhead on the database. You can query V$BLOCK_CHANGE_TRACKING table to determine whether change tracking is enabled and CTWR dba buffer is being used:

SELECT status FROM v$block_change_tracking

If the CTWR process is enabled, you can view the size of the CTWR dba buffer by looking at v$sgastat:

SELECT * FROM v$sgastat WHERE name like ‘CTWR%’;

fast incremental backup failed on standby database

一套Linux上的11.1.0.7的physical standby物理备库在使用fast incremental backup进行高于0级的增量备份时会出现ORA-19648错误,其出错记录如下:

RMAN>  backup incremental level 1 database;

Starting backup at 22-MAR-11
using channel ORA_DISK_1
using channel ORA_DISK_2
channel ORA_DISK_1: starting incremental level 1 datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00002 name=/standby/oradata/SBDB2/datafile/o1_mf_sysaux_22m6ov92_.dbf
input datafile file number=00003 name=/standby/oradata/SBDB2/datafile/o1_mf_undotbs1_23m6ovap_.dbf
input datafile file number=00006 name=/standby/oradata/SBDB2/datafile/o1_mf_enc_25m6ovba_.dbf
channel ORA_DISK_1: starting piece 1 at 22-MAR-11
channel ORA_DISK_2: starting incremental level 1 datafile backup set
channel ORA_DISK_2: specifying datafile(s) in backup set
input datafile file number=00001 name=/standby/oradata/SBDB2/datafile/o1_mf_system_21m6ov92_.dbf
input datafile file number=00005 name=/standby/oradata/SBDB2/datafile/o1_mf_example_24m6ovar_.dbf
input datafile file number=00004 name=/standby/oradata/SBDB2/datafile/o1_mf_users_26m6ovba_.dbf
channel ORA_DISK_2: starting piece 1 at 22-MAR-11
RMAN-03009: failure of backup command on ORA_DISK_1 channel at 03/22/2011 20:20:28
ORA-19648: datafile 2: incremental-start SCN equals checkpoint SCN
ORA-19640: datafile checkpoint is SCN 1249353 time 03/09/2011 05:50:27
continuing other job steps, job failed will not be re-run
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on ORA_DISK_2 channel at 03/22/2011 20:22:33
ORA-19648: datafile 1: incremental-start SCN equals checkpoint SCN
ORA-19640: datafile checkpoint is SCN 1249352 time 03/09/2011 05:50:26

经过分析该ORA-19640->ORA-19648是由11.1.0.7上的Bug引起的,MOS已经确认其为Bug 9288598:

Affects:
Product (Component)	 Oracle Server (Rdbms)
Range of versions believed to be affected	 Versions BELOW 12.1
Versions confirmed as being affected	
11.1.0.7
Platforms affected	 Generic (all / most platforms affected)
Fixed:

This issue is fixed in	
12.1 (Future Release)
11.2.0.2 (Server Patch Set)

An RMAN Backup incremental level 1 can fail with ORA-19648 / ORA-19640 if the standby database is open read only rather than just skipping the datafile.
PROBLEM:
--------
Following error occurring during incremental backup:

Starting backup at 02-DEC-2009 20:37:44
allocated channel: ORA_SBT_TAPE_1
channel ORA_SBT_TAPE_1: SID=154 device type=SBT_TAPE
channel ORA_SBT_TAPE_1: Veritas NetBackup for Oracle - Release 6.5 
(2008052301)
channel ORA_SBT_TAPE_1: starting incremental level 1 datafile backup set
channel ORA_SBT_TAPE_1: specifying datafile(s) in backup set
input datafile file number=00002 
name=/data/ora_data01/KAHCB4P/KAHCB4P_sysaux_01.dbf
input datafile file number=00001 
name=/data/ora_data01/KAHCB4P/KAHCB4P_system_01.dbf
input datafile file number=00003 
name=/data/ora_data01/KAHCB4P/KAHCB4P_undo_01.dbf
input datafile file number=00004 
name=/data/ora_data01/KAHCB4P/KAHCB4P_users_01.dbf
input datafile file number=00005 
name=/data/ora_data01/KAHCB4P/KAHCB4P_tools_01.dbf
input datafile file number=00006 
name=/data/ora_data01/KAHCB4P/KAHCB4P_backup_test_01.dbf
channel ORA_SBT_TAPE_1: starting piece 1 at 02-DEC-2009 20:38:01
RMAN-3009: failure of backup command on ORA_SBT_TAPE_1 channel at 12/02/2009 
20:38:02
ORA-19648: datafile 2: incremental-start SCN equals checkpoint SCN
ORA-19640: datafile checkpoint is SCN 3911695 time 11/27/2009 12:36:48
continuing other job steps, job failed will not be re-run
channel ORA_SBT_TAPE_1: starting incremental level 1 datafile backup set
channel ORA_SBT_TAPE_1: specifying datafile(s) in backup set
including current control file in backup set
including current SPFILE in backup set

DIAGNOSTIC ANALYSIS:
--------------------
Same problem as Bug 6903819
Requested backport, but this hasn't fixed the problem.
Confirmed that the patch was installed correctly and relinked successfully.

RELEASE NOTES:
]]Backup incremental leve 1 fails with ORA-19648 and ORA-19640 when standby
]]database opened for read only.
*** 02/14/10 02:43 pm *** (ADD: Impact/Symptom->FEATURE UNUSABLE )

REDISCOVERY INFORMATION:
Backup incremental level 1 fails with ORA-19648 and the standby database is
open read-only.
WORKAROUND:
None

可以从上述Note中看到该Bug需要到11.2.0.2中才得到fix,那么在11.1.0.7上我们有什么办法能解决或者绕过该问题吗?
经过测试,我得到2种workaround的方法:
该ORA-19648错误首先可以通过在物理备库(physical standby)上停止介质恢复(MRP)进程的方式来workaround:

SQL>  alter database recover managed standby database cancel;
Database altered.

RMAN> backup incremental level 1 database;

Starting backup at 22-MAR-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=141 device type=DISK
allocated channel: ORA_DISK_2
channel ORA_DISK_2: SID=140 device type=DISK
channel ORA_DISK_1: starting incremental level 1 datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00002 name=/standby/oradata/SBDB2/datafile/o1_mf_sysaux_22m6ov92_.dbf
input datafile file number=00004 name=/standby/oradata/SBDB2/datafile/o1_mf_users_26m6ovba_.dbf
input datafile file number=00006 name=/standby/oradata/SBDB2/datafile/o1_mf_enc_25m6ovba_.dbf
channel ORA_DISK_1: starting piece 1 at 22-MAR-11
channel ORA_DISK_2: starting incremental level 1 datafile backup set
channel ORA_DISK_2: specifying datafile(s) in backup set
input datafile file number=00001 name=/standby/oradata/SBDB2/datafile/o1_mf_system_21m6ov92_.dbf
input datafile file number=00003 name=/standby/oradata/SBDB2/datafile/o1_mf_undotbs1_23m6ovap_.dbf
input datafile file number=00005 name=/standby/oradata/SBDB2/datafile/o1_mf_example_24m6ovar_.dbf
channel ORA_DISK_2: starting piece 1 at 22-MAR-11
channel ORA_DISK_1: finished piece 1 at 22-MAR-11
piece handle=/standby/backup/2km7suui_1_1.bak tag=TAG20110322T212538 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:33
channel ORA_DISK_2: finished piece 1 at 22-MAR-11
piece handle=/standby/backup/2lm7suv1_1_1.bak tag=TAG20110322T212538 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:27
Finished backup at 22-MAR-11

Starting Control File and SPFILE Autobackup at 22-MAR-11
piece handle=/standby/backup/c-157018592-20110322-01.bak comment=NONE
Finished Control File and SPFILE Autobackup at 22-MAR-11

该ORA-19648错误也可以通过禁用fast incremental backup的块跟踪(block change tracking)特性来绕过问题,当然在可能的情况下我们更推荐使用上面那种方法,因为毕竟还可以利用到fast incremental backup特性:

SQL> alter database recover managed standby database using current logfile disconnect;
Database altered.

SQL> select process,status from v$managed_standby;

PROCESS   STATUS
--------- ------------
ARCH	  CONNECTED
ARCH	  CONNECTED
ARCH	  CONNECTED
ARCH	  CONNECTED
MRP0	  APPLYING_LOG

SQL> select status from v$block_change_tracking;

STATUS
----------
ENABLED


SQL> alter database disable block change tracking;
Database altered.


RMAN>  backup incremental level 2 database;

Starting backup at 22-MAR-11
using channel ORA_DISK_1
using channel ORA_DISK_2
channel ORA_DISK_1: starting incremental level 2 datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
input datafile file number=00002 name=/standby/oradata/SBDB2/datafile/o1_mf_sysaux_22m6ov92_.dbf
input datafile file number=00004 name=/standby/oradata/SBDB2/datafile/o1_mf_users_26m6ovba_.dbf
input datafile file number=00006 name=/standby/oradata/SBDB2/datafile/o1_mf_enc_25m6ovba_.dbf
channel ORA_DISK_1: starting piece 1 at 22-MAR-11
channel ORA_DISK_2: starting incremental level 2 datafile backup set
channel ORA_DISK_2: specifying datafile(s) in backup set
input datafile file number=00001 name=/standby/oradata/SBDB2/datafile/o1_mf_system_21m6ov92_.dbf
input datafile file number=00003 name=/standby/oradata/SBDB2/datafile/o1_mf_undotbs1_23m6ovap_.dbf
input datafile file number=00005 name=/standby/oradata/SBDB2/datafile/o1_mf_example_24m6ovar_.dbf
channel ORA_DISK_2: starting piece 1 at 22-MAR-11
channel ORA_DISK_1: finished piece 1 at 22-MAR-11
piece handle=/standby/backup/2nm7sv8d_1_1.bak tag=TAG20110322T213052 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:15
channel ORA_DISK_2: finished piece 1 at 22-MAR-11
piece handle=/standby/backup/2om7sv8s_1_1.bak tag=TAG20110322T213052 comment=NONE
channel ORA_DISK_2: backup set complete, elapsed time: 00:00:15
Finished backup at 22-MAR-11

Starting Control File and SPFILE Autobackup at 22-MAR-11
piece handle=/standby/backup/c-157018592-20110322-02.bak comment=NONE
Finished Control File and SPFILE Autobackup at 22-MAR-11

沪ICP备14014813号

沪公网安备 31010802001379号