Re: intermittent long "log file sync" waits

Would suggest to check network latency on the private network

On Tue, 28 Jan 2020 at 9:40 PM, Chris Stephens <cstephens16_at_gmail.com> wrote:

> 3-node Oracle 19.3 RAC
> Centos 7
>
> We have a SQLAlchemy/Python based application workload that is running the
> exact same steps with widely varying response times which appear to be
> related to varying "log file sync" wait times.
>
> Here is a profile of a "fast" run:
>
> CALL-NAME DURATION % CALLS MEAN
> MIN MAX
> ------------------------------ --------- ------ ------ --------
> -------- ---------
> SQL*Net message from client 53.197782 91.8% 10,092 0.005271
> 0.000177 28.568493
> EXEC 3.759177 6.5% 9,816 0.000383
> 0.000000 0.239592
> row cache lock 0.233153 0.4% 541 0.000431
> 0.000113 0.000941
> PARSE 0.140399 0.2% 4,867 0.000029
> 0.000000 0.006620
> DLM cross inst call completion 0.137330 0.2% 956 0.000144
> 0.000004 0.000505
> library cache lock 0.100171 0.2% 215 0.000466
> 0.000151 0.002133
> library cache pin 0.079729 0.1% 216 0.000369
> 0.000056 0.000710
> FETCH 0.058253 0.1% 1,062 0.000055
> 0.000000 0.004148
> log file sync 0.048217 0.1% 149 0.000324
> 0.000259 0.000505
> CLOSE 0.045416 0.1% 4,929 0.000009
> 0.000000 0.000073
> 20 others 0.135624 0.2% 11,854 0.000011
> 0.000000 0.001700
> ------------------------------ --------- ------ ------ --------
> -------- ---------
> TOTAL (30) 57.935251 100.0% 44,697 0.001296
> 0.000000 28.568493
>
> Here is a profile of a "slow" run:
>
> CALL-NAME DURATION % CALLS MEAN
> MIN MAX
> ------------------------------ ---------- ------ ------ --------
> -------- ----------
> SQL*Net message from client 131.186118 61.0% 10,092 0.012999
> 0.000212 106.789360
> log file sync 79.291166 36.8% 150 0.528608
> 0.000264 2.986575
> EXEC 3.728402 1.7% 9,816 0.000380
> 0.000000 0.221403
> row cache lock 0.248868 0.1% 542 0.000459
> 0.000111 0.001036
> PARSE 0.164267 0.1% 4,867 0.000034
> 0.000000 0.004652
> DLM cross inst call completion 0.146981 0.1% 957 0.000154
> 0.000005 0.001188
> library cache lock 0.104354 0.0% 218 0.000479
> 0.000160 0.000728
> library cache pin 0.082504 0.0% 202 0.000408
> 0.000157 0.000672
> FETCH 0.056687 0.0% 1,062 0.000053
> 0.000000 0.003969
> CLOSE 0.043590 0.0% 4,929 0.000009
> 0.000000 0.000180
> 20 others 0.142044 0.1% 11,866 0.000012
> 0.000000 0.001792
> ------------------------------ ---------- ------ ------ --------
> -------- ----------
> TOTAL (30) 215.194981 100.0% 44,701 0.004814
> 0.000000 106.789360
>
> looking at even histogram for that event:
>
> SQL> _at_evh "log file sync"
> EVH_EVENT EVH_WAIT_TIME_MILLI WAIT_COUNT EVH_EST_TIME
> LAST_UPDATE_TIME
> ________________ ______________________ _____________ _______________
> ______________________________________
> log file sync < 1 200051 100.026
> 27-JAN-20 11.39.57.344734 PM -06:00
> log file sync < 2 165 0.248
> 28-JAN-20 12.18.10.429089 AM -06:00
> log file sync < 4 150 0.45
> 27-JAN-20 11.18.31.158102 PM -06:00
> log file sync < 8 199 1.194
> 27-JAN-20 11.19.14.209947 PM -06:00
> log file sync < 16 253 3.036
> 28-JAN-20 08.03.17.851328 AM -06:00
> log file sync < 32 472 11.328
> 27-JAN-20 11.20.22.746033 PM -06:00
> log file sync < 64 728 34.944
> 28-JAN-20 01.13.37.364541 AM -06:00
> log file sync < 128 691 66.336
> 27-JAN-20 11.31.37.400504 PM -06:00
> log file sync < 256 414 79.488
> 28-JAN-20 12.18.10.423987 AM -06:00
> log file sync < 512 405 155.52
> 28-JAN-20 03.27.50.540383 AM -06:00
> log file sync < 1024 459 352.512
> 27-JAN-20 11.35.14.378363 PM -06:00
> log file sync < 2048 482 740.352
> 28-JAN-20 01.18.20.556248 AM -06:00
> log file sync < 4096 576 1769.472
> 27-JAN-20 11.21.05.084998 PM -06:00
> log file sync < 8192 89 546.816
> 27-JAN-20 11.57.36.436460 AM -06:00
> log file sync < 16384 60 737.28
> 25-JAN-20 07.48.31.460408 AM -06:00
> log file sync < 32768 39 958.464
> 27-JAN-20 11.59.09.869286 AM -06:00
> log file sync < 65536 27 1327.104
> 25-JAN-20 09.49.13.856563 AM -06:00
>
> The weird thing is that I don't see corresponding log I/O waits (awaits)
> in iostat output.
>
> I have a ticket open w/ oracle but does anyone have any suggestions to
> discover root cause and/or solution?
>

--
http://www.freelists.org/webpage/oracle-l