From: | Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: standby apply lag on inactive servers |
Date: | 2020-01-31 14:29:00 |
Message-ID: | dc8616a6-f2eb-f1d5-f373-ae042cd61b19@oss.nttdata.com |
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Lists: | pgsql-hackers |
On 2020/01/31 22:40, Alvaro Herrera wrote:
> On 2020-Jan-31, Fujii Masao wrote:
>
>> You're thinking to apply this change to the back branches? Sorry
>> if my understanding is not right. But I don't think that back-patch
>> is ok because it changes the documented existing behavior
>> of pg_last_xact_replay_timestamp(). So it looks like the behavior
>> change not a bug fix.
>
> Yeah, I am thinking in backpatching it. The documented behavior is
> already not what the code does.
Maybe you thought this because getRecordTimestamp() extracts the
timestamp from even WAL record of a restore point? That is, you're
concerned about that pg_last_xact_replay_timestamp() returns the
timestamp of not only commit/abort record but also restore point one.
Right?
As far as I read the code, this problem doesn't occur because
SetLatestXTime() is called only for commit/abort records, in
recoveryStopsAfter(). No?
> Do you have a situation where this
> change would break something? If so, can you please explain what it is?
For example, use the return value of pg_last_xact_replay_timestamp()
(and also the timestamp in the log message output at the end of
recovery) as a HINT when setting recovery_target_time later.
Use it to compare with the timestamp retrieved from the master server,
in order to monitor the replication delay.
Regards,
--
Fujii Masao
NTT DATA CORPORATION
Advanced Platform Technology Group
Research and Development Headquarters
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