Re: intermittent long "log file sync" waits
Date: Tue, 28 Jan 2020 13:20:14 -0600
Message-ID: <CAEFL0szn17WU9kSj7ipRhieXd4w_3hzhU5gSmxDxhx1=WnqDkw_at_mail.gmail.com>
doesn't look like any ash data for lgwr:
SQL> _at_ashtop session_id,blocking_session,event2 1=1 "TIMESTAMP'2020-01-27 15:50:48'" "TIMESTAMP'2020-01-27 15:52:40'"
TOTALSECONDS AAS %This SESSION_ID BLOCKING_SESSION
EVENT2 FIRST_SEEN LAST_SEEN
DIST_SQLEXEC_SEEN
_______________ ______ __________ _____________ ___________________
_____________________ ______________________ ______________________
____________________
81 0.7 82% | 1713 1710 log
file sync 2020-01-27 15:50:54 2020-01-27 15:52:14
1
5 0 5% | 1221 ON CPU
2020-01-27 15:50:59 2020-01-27 15:52:14
1
3 0 3% | 246 ON CPU
2020-01-27 15:51:00 2020-01-27 15:52:00
1
3 0 3% | 1713 ON CPU
2020-01-27 15:50:51 2020-01-27 15:52:27
2
1 0 1% | 123 ON CPU
2020-01-27 15:51:35 2020-01-27 15:51:35
1
1 0 1% | 127 ON CPU
2020-01-27 15:51:50 2020-01-27 15:51:50
1
1 0 1% | 252 2321 latch
free 2020-01-27 15:52:28 2020-01-27 15:52:28
1
1 0 1% | 978 ges
remote message 2020-01-27 15:50:48 2020-01-27 15:50:48
1
1 0 1% | 983 latch
free 2020-01-27 15:52:28 2020-01-27 15:52:28
1
1 0 1% | 1713 library
cache lock 2020-01-27 15:50:48 2020-01-27 15:50:48
1
1 0 1% | 1831 ON CPU
2020-01-27 15:50:49 2020-01-27 15:50:49
1
11 rows selected.
SQL> _at_ashtop session_id,blocking_session,event2 session_id=1710 "TIMESTAMP'2020-01-27 15:50:48'" "TIMESTAMP'2020-01-27 15:52:40'" no rows selected
On Tue, Jan 28, 2020 at 1:09 PM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:
> You’re using v0.2, but v0.6 should be the latest version. 0.2 wouldn’t
> show idle blockers.
>
> I looked at the ashtop output once again. Strange that lgwr processes nor
> any other bg processes show up significantly there. The question is, what
> was lgwr doing while the fg processes were waiting on him.
>
>
>
>
> *Von: *Chris Stephens <cstephens16_at_gmail.com>
> *Datum *Dienstag, 28. Jan. 2020, 7:59 PM
> *An: *Noveljic Nenad <nenad.noveljic_at_vontobel.com>
> *Cc: *oracle-l <Oracle-L_at_freelists.org>
> *Betreff: *Re: intermittent long "log file sync" waits
>
> probably just 19c RAC
>
> SQL> _at_ash_wait_chains event2 session_id=1713 "TIMESTAMP'2020-01-27
> 15:50:48'" "TIMESTAMP'2020-01-27 15:52:40'"
>
> -- Display ASH Wait Chain Signatures script v0.2 BETA by Tanel Poder (
> http://blog.tanelpoder.com )
>
> , TO_CHAR(CASE WHEN session_state = 'WAITING' THEN p1 ELSE null
> END, '0XXXXXXXXXXXXXXX') p1hex
> *
> ERROR at line 14:
> ORA-12850: Could not allocate slaves on all specified instances: 3 needed,
> 1 allocated
>
> SQL>
> Session: c2
>
> On Tue, Jan 28, 2020 at 11:30 AM Noveljic Nenad <
> nenad.noveljic_at_vontobel.com> wrote:
>
>> The script should work with 19. It must be something else. Could you try
>> with ash_wait_chains2 - 2 is the rac version? For start, I would group only
>> on event2 (the first parameter).
>>
>> If it doesn’t work, please post the error message.
>>
>>
>>
>> *Von: *Chris Stephens <cstephens16_at_gmail.com>
>> *Datum *Dienstag, 28. Jan. 2020, 5:43 PM
>> *An: *Noveljic Nenad <nenad.noveljic_at_vontobel.com>
>> *Cc: *oracle-l <Oracle-L_at_freelists.org>
>> *Betreff: *Re: intermittent long "log file sync" waits
>>
>> unfortunately, ash_wait_chains.sql doesn't work on 19.3 but here is
>> ashtop showing foreground process blocked on lgwr (1710):
>>
>> SQL> _at_ashtop inst_id,username,blocking_session,blocking_inst_id,event2
>> 1=1 "TIMESTAMP'2020-01-27 15:50:48'" "TIMESTAMP'2020-01-27 15:52:40'"
>> TOTALSECONDS AAS %This INST_ID USERNAME
>> BLOCKING_SESSION BLOCKING_INST_ID EVENT2
>> FIRST_SEEN LAST_SEEN DIST_SQLEXEC_SEEN
>> _______________ ______ __________ __________ ________________
>> ___________________ ___________________ _____________________
>> ______________________ ______________________ ____________________
>> 81 0.7 82% | 2 GEN3_MGOWER_3
>> 1710 2 log file sync 2020-01-27 15:50:54
>> 2020-01-27 15:52:14 1
>> 9 0.1 9% | 1 SYS
>> ON CPU 2020-01-27 15:50:49
>> 2020-01-27 15:52:14 1
>> 3 0 3% | 2 GEN3_MGOWER_3
>> ON CPU 2020-01-27 15:50:51
>> 2020-01-27 15:52:27 2
>> 2 0 2% | 2 SYS
>> ON CPU 2020-01-27 15:51:35
>> 2020-01-27 15:51:40 1
>> 1 0 1% | 2 GEN3_MGOWER_3
>> library cache lock 2020-01-27 15:50:48
>> 2020-01-27 15:50:48 1
>> 1 0 1% | 2 SYS
>> 2321 2 latch free 2020-01-27 15:52:28
>> 2020-01-27 15:52:28 1
>> 1 0 1% | 2 SYS
>> ges remote message 2020-01-27 15:50:48
>> 2020-01-27 15:50:48 1
>> 1 0 1% | 2 SYS
>> latch free 2020-01-27 15:52:28
>> 2020-01-27 15:52:28 1
>>
>>
>> 8 rows selected.
>>
>> SQL> _at_bg lgwr
>> NAME DESCRIPTION SID OPID SPID PADDR
>> SADDR
>> _______ ______________ _______ _______ ________ ___________________
>> ___________________
>> LGWR Redo etc. 1710 34 26552 00000001E8718860
>> 00000001D8BFF4A0
>>
>> On Tue, Jan 28, 2020 at 10:25 AM Noveljic Nenad <
>> nenad.noveljic_at_vontobel.com> wrote:
>>
>>> Hi Chris,
>>>
>>>
>>>
>>> log file sync measures much more than IO.
>>>
>>>
>>>
>>> First of all, I’d run Tanel’s ash_wait_chains (
>>> https://github.com/tanelpoder/tpt-oracle/blob/master/ash/ash_wait_chains.sql
>>> ), because if often points straightly to the root cause .
>>>
>>>
>>>
>>> Here’s is a usage example, when intermittent log file sync waits where
>>> caused by slow control file writes:
>>> https://nenadnoveljic.com/blog/bad-commit-performance-control-file-writes/
>>> .
>>>
>>>
>>>
>>> Best regards,
>>>
>>>
>>> Nenad
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
>>> Behalf Of *Chris Stephens
>>> *Sent:* Dienstag, 28. Januar 2020 17:09
>>> *To:* oracle-l <Oracle-L_at_freelists.org>
>>> *Subject:* intermittent long "log file sync" waits
>>>
>>>
>>>
>>> 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?
>>>
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