PostgreSQL debug log doesn't record whole procedure(from receiving request to sending response)

Hi,
We recently encounter one issue about PostgreSQL ODBC client doesn’t receive response from PostgreSQL server in time (client set 5 seconds timeout) occasionally (1 or 2 times per 24 hours). Both PostgreSQL and its client are deployed in VM against. It took us days to debug where cause the timeout. We enable PostgreSQL server debug log via below configuration.

log_min_messages = debug5
log_min_error_statement = debug5
log_line_prefix = '[%p-%c-%l] %m <%h %i> '
log_error_verbosity = verbose
log_statement = 'all'
logging_collector = on
log_destination = 'stderr'
log_directory = '/tmp'
log_filename = 'postgresql-%Y-%m-%d_%H%M%S.log'
log_duration = on
log_autovacuum_min_duration = 2

Client log indicate it received response 10 seconds after sending the request:

Nov 13 22:25:58 CFPU-0 rnwman[2701607]: RU:OMU-0|PNAME:QNRNWMAN|LPID:2701607|PID:0x50A 0x11 0x0|TIME:2021-11-14 00:25:58:050678|TEXT:WQTST before call db:1|DATA:
Nov 13 22:25:58 CFPU-0 raktor[2701622]: RU:OMU-0|PNAME:QNRAKTOR|LPID:2701622|PID:0x4EE 0x31 0x0|TIME:2021-11-14 00:26:03:054718|TEXT:RAV:set_wcel_state_r-db response timeout|DATA:
Nov 13 22:26:08 CFPU-0 rnwman[2701607]: RU:OMU-0|PNAME:QNRNWMAN|LPID:2701607|PID:0x50A 0x11 0x0|TIME:2021-11-14 00:26:08:012336|TEXT:RAV Exit: set_wcel_state__r:= |DATA:
Nov 13 22:26:08 CFPU-0 rnwman[2701607]: RU:OMU-0|PNAME:QNRNWMAN|LPID:2701607|PID:0x50A 0x11 0x0|TIME:2021-11-14 00:26:08:012501|TEXT:WQTST after call db:1|DATA:

While PostgreSQL log recorded for the procedure indicate it executed quickly.

[2701833-618d1b70.293a09-173237] 2021-11-13 22:25:58.050 GMT <169.254.0.21 idle> DEBUG: 00000: StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173238] 2021-11-13 22:25:58.050 GMT <169.254.0.21 idle> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173239] 2021-11-13 22:25:58.050 GMT <169.254.0.21 idle> STATEMENT: DEALLOCATE "_PLAN0x7f2ec021ab60"
[2701833-618d1b70.293a09-173240] 2021-11-13 22:25:58.050 GMT <169.254.0.21 idle> LOG: 00000: statement: DEALLOCATE "_PLAN0x7f2ec021ab60"
[2701833-618d1b70.293a09-173241] 2021-11-13 22:25:58.050 GMT <169.254.0.21 idle> LOCATION: exec_simple_query, postgres.c:1042
[2701833-618d1b70.293a09-173242] 2021-11-13 22:25:58.050 GMT <169.254.0.21 DEALLOCATE> DEBUG: 00000: CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173243] 2021-11-13 22:25:58.050 GMT <169.254.0.21 DEALLOCATE> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173244] 2021-11-13 22:25:58.050 GMT <169.254.0.21 DEALLOCATE> STATEMENT: DEALLOCATE "_PLAN0x7f2ec021ab60"
[2701833-618d1b70.293a09-173245] 2021-11-13 22:25:58.050 GMT <169.254.0.21 DEALLOCATE> LOG: 00000: duration: 0.098 ms
[2701833-618d1b70.293a09-173246] 2021-11-13 22:25:58.050 GMT <169.254.0.21 DEALLOCATE> LOCATION: exec_simple_query, postgres.c:1287
[2701833-618d1b70.293a09-173247] 2021-11-13 22:25:58.050 GMT <169.254.0.21 PARSE> DEBUG: 00000: parse _PLAN0x7f2ec021ab60: UPDATE act_wcel SET wcel_state=$1 WHERE wbts_id=74 and lcr_id=7402
[2701833-618d1b70.293a09-173248] 2021-11-13 22:25:58.050 GMT <169.254.0.21 PARSE> LOCATION: exec_parse_message, postgres.c:1342
[2701833-618d1b70.293a09-173249] 2021-11-13 22:25:58.050 GMT <169.254.0.21 PARSE> STATEMENT: UPDATE act_wcel SET wcel_state=$1 WHERE wbts_id=74 and lcr_id=7402
[2701833-618d1b70.293a09-173250] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> DEBUG: 00000: StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173251] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173252] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> STATEMENT: UPDATE act_wcel SET wcel_state=$1 WHERE wbts_id=74 and lcr_id=7402
[2701833-618d1b70.293a09-173253] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> LOG: 00000: duration: 0.089 ms
[2701833-618d1b70.293a09-173254] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> LOCATION: exec_parse_message, postgres.c:1550
[2701833-618d1b70.293a09-173255] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> DEBUG: 00000: CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173256] 2021-11-13 22:25:58.051 GMT <169.254.0.21 PARSE> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173257] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> DEBUG: 00000: StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173258] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173259] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> DEBUG: 00000: CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173260] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173261] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> DEBUG: 00000: bind <unnamed> to _PLAN0x7f2ec021ab60
[2701833-618d1b70.293a09-173262] 2021-11-13 22:25:58.051 GMT <169.254.0.21 idle> LOCATION: exec_bind_message, postgres.c:1600
[2701833-618d1b70.293a09-173263] 2021-11-13 22:25:58.051 GMT <169.254.0.21 BIND> DEBUG: 00000: StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
[2701833-618d1b70.293a09-173264] 2021-11-13 22:25:58.051 GMT <169.254.0.21 BIND> LOCATION: ShowTransactionStateRec, xact.c:5333
[2701833-618d1b70.293a09-173265] 2021-11-13 22:25:58.051 GMT <169.254.0.21 BIND> STATEMENT: UPDATE act_wcel SET wcel_state=$1 WHERE wbts_id=74 and lcr_id=7402
[2701833-618d1b70.293a09-173266] 2021-11-13 22:25:58.051 GMT <169.254.0.21 BIND> LOG: 00000: duration: 0.107 ms
[2701833-618d1b70.293a09-173267] 2021-11-13 22:25:58.051 GMT <169.254.0.21 BIND> LOCATION: exec_bind_message, postgres.c:1917
[2701833-618d1b70.293a09-173268] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> LOG: 00000: execute _PLAN0x7f2ec021ab60: UPDATE act_wcel SET wcel_state=$1 WHERE wbts_id=74 and lcr_id=7402
[2701833-618d1b70.293a09-173269] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> DETAIL: parameters: $1 = '0'
[2701833-618d1b70.293a09-173270] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> LOCATION: exec_execute_message, postgres.c:2055
[2701833-618d1b70.293a09-173271] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> LOG: 00000: duration: 0.080 ms
[2701833-618d1b70.293a09-173272] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> LOCATION: exec_execute_message, postgres.c:2138
[2701833-618d1b70.293a09-173273] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> DEBUG: 00000: CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 23280/1/1
[2701833-618d1b70.293a09-173274] 2021-11-13 22:25:58.051 GMT <169.254.0.21 UPDATE> LOCATION: ShowTransactionStateRec, xact.c:5333

Finally, the tcpdump indicate the delay happened at PostgreSQL server.

[cid:image002(dot)jpg(at)01D7DA05(dot)A24D3720]

This mail is not to investigate why PostgreSQL server delay sending the response message. We suspect the backend I/O performance issue.
This mail is to ask why PostgreSQL debug log doesn’t really include the response message delay which may cause misleading why troubleshooting. It looks to me the debug log doesn’t record the whole procedure. If there are some developer options include the missing part but we didn’t enable?

Best Regards
It always takes longer than you expect,
even when you take into account
----------------------------------------------------------------------------------------------
Yan-Jack Chen (陈雁)
Tel: +8613957141340
Addr: No.567 XinCheng Rd, Binjiang District, Hangzhou, China, 310053