AIX: very (I repeat) slow DBWR

Hai Folks,

I have a huge performance problem with the DBWR-proces(ses) on an AIX 4.2.1. While the redo-logs (4x50Mb) get filled in a couple of minutes
(during which there is high IO on the disk containing them), the
checkpointing (which starts when a redo-log is half-full) takes more than an hour, resulting, of course, in locking up when all of the redo-logs are full.

The data-files of the tablespace being loaded via import, are on one SSA-disk. This disk also contains the log of the Journaled File System. The DBWR(s) show(s) activity of around 70-80. But iostat (5 sec sample) shows:

Disks:        % tm_act     Kbps      tps    Kb_read   Kb_wrtn
hdisk3_b         4.0      16.8       4.2          0        84
hdisk3_d         0.0       0.0       0.0          0         0
hdisk3_e         0.0       0.0       0.0          0         0
hdisk3_g         0.0       0.0       0.0          0         0
hdisk4_b         9.4      31.9       8.0          0       160
hdisk4_d         0.0       0.0       0.0          0         0
hdisk4_e         0.0       0.0       0.0          0         0
hdisk4_g         0.0       0.0       0.0          0         0

hdisk3_b and hdisk4_b each contain a copy of the JFS-log, so less than 80 Kb were written to the data-files in 5 seconds.

I started with 4 DBWR-processes with use_async_io = false, then switched to async_io which resulted in the DBWR doing all the work (sic) and the 4 child-processes idling. Same lack of performance.

A very funny symptom: I just shut down abort the database, but the dbwr kept running for a while, never saw that before. See for yourself: SVRMGR> shutdown
^CORA-01013: user requested cancel of current operation Database dismounted.
^CORA-01013: user requested cancel of current operation SVRMGR> shutdown abort
ORACLE instance shut down.
SVRMGR> host ps -fu orapre | grep MIS
  orapre 22952 25970 5 09:39:38 pts/0 0:00 grep MIS   orapre 26228 25970 0 09:25:29 - 0:00 oracleMIS
(DESCRIPTION=(LOCAL=YES

)(ADDRESS=(PROTOCOL=beq)))
  orapre 34194 1 69 23:17:19 - 287:26 ora_dbwr_MIS SVRMGR> exit
Server Manager complete.

Any brightness is, as always, welcome.
--
Kind Regards,

Gerard Received on Wed May 05 1999 - 03:06:49 CDT