RE: intermittent long "log file sync" waits
Date: Tue, 28 Jan 2020 17:29:59 +0000
Message-ID: <39760_1580232621_5E306FAD_39760_6519_1_238f704e660247f78d5e2f6a5c98b27f_at_vontobel.com>
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<mailto:cstephens16_at_gmail.com>>
Datum Dienstag, 28. Jan. 2020, 5:43 PM
unfortunately, ash_wait_chains.sql doesn't work on 19.3 but here is ashtop showing foreground process blocked on lgwr (1710):
8 rows selected.
SQL> _at_bg lgwr
NAME DESCRIPTION SID OPID SPID PADDR SADDR
On Tue, Jan 28, 2020 at 10:25 AM Noveljic Nenad <nenad.noveljic_at_vontobel.com<mailto: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<mailto:oracle-l-bounce_at_freelists.org> <oracle-l-bounce_at_freelists.org<mailto:oracle-l-bounce_at_freelists.org>> On Behalf Of Chris Stephens
Sent: Dienstag, 28. Januar 2020 17:09
An: Noveljic Nenad <nenad.noveljic_at_vontobel.com<mailto:nenad.noveljic_at_vontobel.com>>
Cc: oracle-l <Oracle-L_at_freelists.org<mailto:Oracle-L_at_freelists.org>>
Betreff: Re: intermittent long "log file sync" waits
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
_______ ______________ _______ _______ ________ ___________________ ___________________
LGWR Redo etc. 1710 34 26552 00000001E8718860 00000001D8BFF4A0
To: oracle-l <Oracle-L_at_freelists.org<mailto:Oracle-L_at_freelists.org>>
3-node Oracle 19.3 RAC
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:
Here is a profile of a "slow" run:
looking at even histogram for that event:
SQL> _at_evh "log file sync"
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?
Important Notice
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Centos 7
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
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
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
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Received on Tue Jan 28 2020 - 18:29:59 CET