On 06/19/2015 01:05 PM, Paula Price wrote:
On Fri, Jun 19, 2015 at 12:01 PM, Adrian Klaver
<adrian.klaver@xxxxxxxxxxx <mailto:adrian.klaver@xxxxxxxxxxx>> wrote:
On 06/18/2015 05:45 PM, Paula Price wrote:
I have Postgresql 9.2.10 streaming replication set up with log
shipping in
case the replication falls behind. I discovered that the
log-shipping had
been disabled at some point in time. I enabled the log shipping
again.
If at some point in time the streaming replication fell behind
and the
standby server was not able to retrieve the necessary WAL
file(s) from the
primary, would the standby server continue to function
normally? Do I need
to rebuild the standby server? I have restarted the standby
server and it
is up and running with no issues.
Well that seems at odds with it being unable to retrieve the WAL
files. This leads to these questions:
1) What makes you think it did not retrieve the WAL files via streaming?
It _may_ _not _have fallen behind via replication. We do have standby
servers that fall behind, but since we have log-shipping it is not a
concern. On this server, i have no idea how long we were running
without log-shipping. I have no idea how many log files I would have to
go through to find out when log-shipping stopped.
My basic question is:
If a standby server falls behind with streaming replication AND the
standby server cannot obtain the WAL file needed from the primary, will
you get an error from the standby server? Or does it just hiccup and
try to carry on?
No it will fall over:
http://www.postgresql.org/docs/9.2/interactive/runtime-config-replication.html#RUNTIME-CONFIG-REPLICATION-SENDER
wal_keep_segments (integer)
Specifies the minimum number of past log file segments kept in the
pg_xlog directory, in case a standby server needs to fetch them for
streaming replication. Each segment is normally 16 megabytes. If a
standby server connected to the sending server falls behind by more than
wal_keep_segments segments, the sending server might remove a WAL
segment still needed by the standby, in which case the replication
connection will be terminated. Downstream connections will also
eventually fail as a result. (However, the standby server can recover by
fetching the segment from archive, if WAL archiving is in use.)
This sets only the minimum number of segments retained in pg_xlog;
the system might need to retain more segments for WAL archival or to
recover from a checkpoint. If wal_keep_segments is zero (the default),
the system doesn't keep any extra segments for standby purposes, so the
number of old WAL segments available to standby servers is a function of
the location of the previous checkpoint and status of WAL archiving.
This parameter can only be set in the postgresql.conf file or on the
server command line.
When you started up if the necessary WAL files where not on the server
you would have seen Postgres throwing errors in the log.
I would check out the below to verify:
http://www.postgresql.org/docs/9.2/interactive/warm-standby.html#STREAMING-REPLICATION
25.2.5.2. Monitoring
2) What does the postgres log show at the time you restarted the
standby?
2015-06-18 01:12:41.871 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOG: 00000: database system was shut down in recovery at
2015-06-18 01:12:14 UTC
2015-06-18 01:12:41.871 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOCATION: StartupXLOG, xlog.c:6298
2015-06-18 01:12:41.904 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOG: 00000: entering standby mode
2015-06-18 01:12:41.904 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOCATION: StartupXLOG, xlog.c:6384
2015-06-18 01:12:41.987 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOG: 00000: redo starts at 867/FDF32E18
2015-06-18 01:12:41.987 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOCATION: StartupXLOG, xlog.c:6855
2015-06-18 01:12:42.486
UTC::[unknown]@[unknown]:[28213]:2015-06-18 01:12:42 UTC: LOG:
00000: connection received: host=[local]
2015-06-18 01:12:42.486
UTC::[unknown]@[unknown]:[28213]:2015-06-18 01:12:42 UTC:
LOCATION: BackendInitialize, postmaster.c:3501
2015-06-18 01:12:42.486
UTC:[local]:postgres@postgres:[28213]:2015-06-18 01:12:42 UTC:
FATAL: 57P03: the database system is starting up
2015-06-18 01:12:42.486
UTC:[local]:postgres@postgres:[28213]:2015-06-18 01:12:42 UTC:
LOCATION: ProcessStartupPacket, postmaster.c:1792
2015-06-18 01:12:43.488
UTC::[unknown]@[unknown]:[28270]:2015-06-18 01:12:43 UTC: LOG:
00000: connection received: host=[local]
2015-06-18 01:12:43.488
UTC::[unknown]@[unknown]:[28270]:2015-06-18 01:12:43 UTC:
LOCATION: BackendInitialize, postmaster.c:3501
2015-06-18 01:12:43.488
UTC:[local]:postgres@postgres:[28270]:2015-06-18 01:12:43 UTC:
FATAL: 57P03: the database system is starting up
2015-06-18 01:12:43.488
UTC:[local]:postgres@postgres:[28270]:2015-06-18 01:12:43 UTC:
LOCATION: ProcessStartupPacket, postmaster.c:1792
2015-06-18 01:12:44.489
UTC::[unknown]@[unknown]:[28327]:2015-06-18 01:12:44 UTC: LOG:
00000: connection received: host=[local]
2015-06-18 01:12:44.489
UTC::[unknown]@[unknown]:[28327]:2015-06-18 01:12:44 UTC:
LOCATION: BackendInitialize, postmaster.c:3501
2015-06-18 01:12:44.489
UTC:[local]:postgres@postgres:[28327]:2015-06-18 01:12:44 UTC:
FATAL: 57P03: the database system is starting up
2015-06-18 01:12:44.489
UTC:[local]:postgres@postgres:[28327]:2015-06-18 01:12:44 UTC:
LOCATION: ProcessStartupPacket, postmaster.c:1792
2015-06-18 01:12:44.490 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOG: 00000: consistent recovery state reached at 868/112AF7F8
2015-06-18 01:12:44.490 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOCATION: CheckRecoveryConsistency, xlog.c:7405
2015-06-18 01:12:44.490 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOG: 00000: invalid record length at 868/112AFB00
2015-06-18 01:12:44.490 UTC::@:[28168]:2015-06-18 01:12:41 UTC:
LOCATION: ReadRecord, xlog.c:4078
2015-06-18 01:12:44.490 UTC::@:[28166]:2015-06-18 01:12:41 UTC:
LOG: 00000: database system is ready to accept read only
connections
2015-06-18 01:12:44.490 UTC::@:[28166]:2015-06-18 01:12:41 UTC:
LOCATION: sigusr1_handler, postmaster.c:4314
I need to know if the
data integrity has been compromised.
I have run this query to determine the lag time for the
standby(in case
this tells me anything):
"SELECT now(), now() - pg_last_xact_replay_timestamp() AS time_lag;
RESULT:
"2015-06-19 00:40:48.83701+00";"00:00:01.078616"
Thank you,
Paula P
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx <mailto:adrian.klaver@xxxxxxxxxxx>
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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