Re: intermittent long "log file sync" waits
Date: Tue, 28 Jan 2020 12:59:21 -0600
Message-ID: <CAEFL0szP5+-ZUog8Q=P0TiusLw6MpDDM46hZM=7ps0v0o3p_OQ_at_mail.gmail.com>
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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