Expected Log Write Time

My log writer trace file shows certain hours where Oracle is issuing warning on log write times.
Warning: log write time 4990ms, size 105KB
*** 2012-03-14 23:52:25.948
Warning: log write time 4130ms, size 95KB
*** 2012-03-14 23:52:32.629
Warning: log write time 6680ms, size 425KB
*** 2012-03-14 23:52:57.560
Warning: log write time 1100ms, size 1KB
*** 2012-03-14 23:52:59.406
Warning: log write time 1850ms, size 25KB

Anybody know what range in terms of time is considered reasonable?
xoxomosAsked:
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DavidSenior Oracle Database AdministratorCommented:
Unfortunately, your examples are all taken from a 35 second window, so we cannot guess if you have a pattern or just a random act of electrons.  I'd like to see a better log sample, as well as the undo log sizing before I say more.
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xoxomosAuthor Commented:
Warning: log write time 670ms, size 15KB
*** 2012-03-14 23:41:09.686
Warning: log write time 650ms, size 44KB
*** 2012-03-14 23:41:13.499
Warning: log write time 560ms, size 33KB
*** 2012-03-14 23:41:14.611
Warning: log write time 1110ms, size 41KB
*** 2012-03-14 23:41:15.218
Warning: log write time 600ms, size 118KB
*** 2012-03-14 23:41:18.037
Warning: log write time 1830ms, size 181KB
*** 2012-03-14 23:41:26.497
Warning: log write time 650ms, size 2KB
*** 2012-03-14 23:41:55.942
Warning: log write time 660ms, size 5KB
*** 2012-03-14 23:41:56.593
Warning: log write time 650ms, size 76KB
*** 2012-03-14 23:42:28.664
Warning: log write time 1080ms, size 13KB
*** 2012-03-14 23:42:32.287
Warning: log write time 3620ms, size 142KB
*** 2012-03-14 23:42:39.323
Warning: log write time 7030ms, size 201KB
*** 2012-03-14 23:42:41.427
Warning: log write time 2100ms, size 75KB
*** 2012-03-14 23:42:43.625
Warning: log write time 1970ms, size 70KB
*** 2012-03-14 23:42:55.727
Warning: log write time 830ms, size 1KB
*** 2012-03-14 23:43:06.016

Warning: log write time 5130ms, size 81KB
*** 2012-03-14 23:37:21.997
Warning: log write time 13060ms, size 542KB
*** 2012-03-14 23:37:26.248
Warning: log write time 4240ms, size 3468KB
*** 2012-03-14 23:37:28.400
Warning: log write time 2140ms, size 1223KB
*** 2012-03-14 23:37:36.152
Warning: log write time 1630ms, size 1KB
*** 2012-03-14 23:38:28.250
Warning: log write time 52060ms, size 15028KB
*** 2012-03-14 23:38:29.001
Warning: log write time 730ms, size 475KB
*** 2012-03-14 23:38:29.588
Warning: log write time 590ms, size 721KB
*** 2012-03-14 23:38:49.022
Warning: log write time 660ms, size 22KB
*** 2012-03-14 23:38:53.658
Warning: log write time 1870ms, size 52KB
*** 2012-03-14 23:38:58.756
Warning: log write time 5100ms, size 171KB
*** 2012-03-14 23:39:01.082
Warning: log write time 2320ms, size 241KB
*** 2012-03-14 23:39:30.083
Warning: log write time 760ms, size 51KB
*** 2012-03-14 23:39:32.784
Warning: log write time 2700ms, size 69KB
*** 2012-03-14 23:39:39.241
Warning: log write time 6450ms, size 295KB
*** 2012-03-14 23:39:40.071
Warning: log write time 820ms, size 709KB
*** 2012-03-14 23:39:40.756
Warning: log write time 600ms, size 36KB
*** 2012-03-14 23:39:42.781
Warning: log write time 590ms, size 4KB
*** 2012-03-14 23:40:04.558
Warning: log write time 1160ms, size 69KB
*** 2012-03-14 23:40:08.043
Warning: log write time 3490ms, size 143KB
*** 2012-03-14 23:40:10.835
Warning: log write time 2790ms, size 385KB
*** 2012-03-14 23:40:11.575
Warning: log write time 740ms, size 240KB
*** 2012-03-14 23:40:35.722
Warning: log write time 1680ms, size 73KB
*** 2012-03-14 23:40:40.160
Warning: log write time 4440ms, size 71KB

*** 2012-03-14 23:34:15.241
Warning: log write time 900ms, size 33KB
*** 2012-03-14 23:35:06.058
Warning: log write time 1010ms, size 2KB
*** 2012-03-14 23:35:14.370
Warning: log write time 630ms, size 0KB
*** 2012-03-14 23:35:18.937
Warning: log write time 4570ms, size 68KB
*** 2012-03-14 23:35:26.926
Warning: log write time 7990ms, size 293KB
*** 2012-03-14 23:35:35.988
Warning: log write time 9060ms, size 393KB
*** 2012-03-14 23:35:36.640
Warning: log write time 650ms, size 589KB
*** 2012-03-14 23:35:51.910
Warning: log write time 1390ms, size 17KB
*** 2012-03-14 23:35:56.742
Warning: log write time 4830ms, size 64KB
*** 2012-03-14 23:36:00.912
Warning: log write time 4160ms, size 258KB
*** 2012-03-14 23:36:03.163
Warning: log write time 1540ms, size 111KB
*** 2012-03-14 23:36:08.024
Warning: log write time 4760ms, size 136KB
*** 2012-03-14 23:36:09.299
Warning: log write time 1270ms, size 302KB
*** 2012-03-14 23:36:26.394
Warning: log write time 510ms, size 18KB
*** 2012-03-14 23:36:28.216
Warning: log write time 1820ms, size 32KB
*** 2012-03-14 23:36:29.275
Warning: log write time 1060ms, size 92KB
*** 2012-03-14 23:36:31.469
Warning: log write time 1990ms, size 24KB
*** 2012-03-14 23:36:33.396
Warning: log write time 1930ms, size 116KB
*** 2012-03-14 23:36:34.182
Warning: log write time 770ms, size 145KB
*** 2012-03-14 23:36:37.866
Warning: log write time 1540ms, size 23KB
*** 2012-03-14 23:36:38.536
Warning: log write time 670ms, size 108KB
*** 2012-03-14 23:36:44.150
Warning: log write time 530ms, size 93KB
*** 2012-03-14 23:37:08.931
Warning: log write time 5130ms, size 81KB
*** 2012-03-14 23:37:21.997

Warning: log write time 700ms, size 21KB
*** 2012-03-14 23:31:38.068
Warning: log write time 510ms, size 18KB
*** 2012-03-14 23:31:39.504
Warning: log write time 1430ms, size 24KB
*** 2012-03-14 23:31:40.854
Warning: log write time 1350ms, size 107KB
*** 2012-03-14 23:31:43.131
Warning: log write time 2270ms, size 49KB
*** 2012-03-14 23:31:45.921
Warning: log write time 2790ms, size 141KB
*** 2012-03-14 23:31:47.584
Warning: log write time 1660ms, size 144KB
*** 2012-03-14 23:32:06.162
Warning: log write time 810ms, size 1KB
*** 2012-03-14 23:32:14.728
Warning: log write time 540ms, size 58KB
*** 2012-03-14 23:32:22.774
Warning: log write time 730ms, size 13KB
*** 2012-03-14 23:32:24.126
Warning: log write time 1350ms, size 77KB
*** 2012-03-14 23:32:24.687
Warning: log write time 560ms, size 78KB
*** 2012-03-14 23:32:25.895
Warning: log write time 770ms, size 30KB
*** 2012-03-14 23:32:27.772
Warning: log write time 510ms, size 3KB
*** 2012-03-14 23:32:37.631
Warning: log write time 1380ms, size 36KB
*** 2012-03-14 23:32:38.281
Warning: log write time 650ms, size 61KB
*** 2012-03-14 23:32:46.552
Warning: log write time 830ms, size 11KB
*** 2012-03-14 23:32:47.061
Warning: log write time 500ms, size 53KB
*** 2012-03-14 23:32:50.646
Warning: log write time 1110ms, size 5KB
*** 2012-03-14 23:34:09.350
Warning: log write time 860ms, size 5KB
*** 2012-03-14 23:34:11.571
Warning: log write time 2200ms, size 66KB
*** 2012-03-14 23:34:12.429
Warning: log write time 860ms, size 138KB
*** 2012-03-14 23:34:13.568
Warning: log write time 1140ms, size 103KB
*** 2012-03-14 23:34:15.241
Warning: log write time 900ms, size 33KB

*** 2012-03-14 23:29:25.601
Warning: log write time 530ms, size 2KB
*** 2012-03-14 23:29:36.006
Warning: log write time 1120ms, size 2KB
*** 2012-03-14 23:29:37.045
Warning: log write time 1040ms, size 14KB
*** 2012-03-14 23:29:38.553
Warning: log write time 1510ms, size 29KB
*** 2012-03-14 23:29:39.251
Warning: log write time 700ms, size 20KB
*** 2012-03-14 23:29:41.123
Warning: log write time 600ms, size 5KB
*** 2012-03-14 23:29:42.248
Warning: log write time 1120ms, size 25KB
*** 2012-03-14 23:29:44.436
Warning: log write time 1580ms, size 37KB
*** 2012-03-14 23:29:45.717
Warning: log write time 1280ms, size 44KB
*** 2012-03-14 23:29:47.820
Warning: log write time 1830ms, size 26KB
*** 2012-03-14 23:29:50.189
Warning: log write time 790ms, size 169KB
*** 2012-03-14 23:30:10.981
Warning: log write time 570ms, size 9KB
*** 2012-03-14 23:30:13.061
Warning: log write time 2080ms, size 35KB
*** 2012-03-14 23:30:13.590
Warning: log write time 530ms, size 129KB
*** 2012-03-14 23:30:14.407
Warning: log write time 810ms, size 43KB
*** 2012-03-14 23:30:19.015
Warning: log write time 630ms, size 24KB
*** 2012-03-14 23:30:25.872 56967 kcrr.c
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xoxomosAuthor Commented:
ACTUAL UNDO SIZE [MByte] UNDO RETENTION [Sec]      NEEDED UNDO SIZE [MByte]
------------------------ ------------------------- ------------------------
                    2048 900                                     54.2109375
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Chakravarthi AyyalaDatabase AdministratorCommented:
Certainly more than a sec (1000ms) is not acceptable from my experience.
What is the storage for your online redo logs?
Hope you are not using RAID 5.
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Geert GOracle dbaCommented:
check in the virusscanner for the exclusions of the datafiles, redologs and controlfiles
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xoxomosAuthor Commented:
No, we are not on RAID5.  I am suspecting some sort of i/o contention.
0
Chakravarthi AyyalaDatabase AdministratorCommented:
Do you see any CPU spent for i/o?
0
xoxomosAuthor Commented:
Very little.  Most times there's a big surplus of CPU :-)
0
Chakravarthi AyyalaDatabase AdministratorCommented:
Are you using AMM?
What is the size of your log_buffer?
0
xoxomosAuthor Commented:
No AMM.  
log_buffer                           integer
16006144
SQL>
Interesting you'd mention that.  As I understand now this log_buffer is pretty much assigned by Oracle so that's the default.  I tried to make it smaller but no.  The other option I had considered since I could not make log_buffer smaller was make redo logs larger.  Currently they are 100mb.
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Chakravarthi AyyalaDatabase AdministratorCommented:
Irrespective of redo log size, i had seen Oracle rotating the redo logs at smaller sizes.
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Chakravarthi AyyalaDatabase AdministratorCommented:
Checking further to see if i post anything that will help you.
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Chakravarthi AyyalaDatabase AdministratorCommented:
also did you do a truss on the lgwr process and see the timings for thread_post and thread_Wait?
0
xoxomosAuthor Commented:
No.
"Word of caution, don't truss LGWR or any background process unless it is absolutely necessary. You can accidentally cause performance issues, worse yet, ..." :-)
0
Chakravarthi AyyalaDatabase AdministratorCommented:
Thanks.
I think we use truss only if there is a performance issue. :)
0
xoxomosAuthor Commented:
Right now we're not having performance issue and it's finals week :-)
The learning system was down most of yesterday because someone felt the need to move from 3Par to NetApp, they could not wait a week and needless to say the move did not go perfectly so i'm avoiding anything that might have an impact that will have the students even madder. :-)
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Chakravarthi AyyalaDatabase AdministratorCommented:
Oh! ok.
Ya. Obviously you know best about your environment.
Will see what best inputs can be provided here.
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xoxomosAuthor Commented:
Quarter ends Wed.
0
xoxomosAuthor Commented:
Thanks,
It appears something unusual was happening during that time.  The data center was moving, cables were being dehooked , rehooked and re-rehooked etc but now things seem to have returned to normal.
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