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Re: Reporting WAL file containing checkpoint's REDO record in pg_controldata's result

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Jaime Casanova <jaime(at)2ndquadrant(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Reporting WAL file containing checkpoint's REDO record in pg_controldata's result
Date: 2012-03-23 09:51:10
Message-ID: CAHGQGwFas83BLg+PApHBiSn5GF=y1-BxkR_TXbbYfSM3num4CQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Mar 23, 2012 at 2:06 PM, Jaime Casanova <jaime(at)2ndquadrant(dot)com> wrote:
> On Thu, Mar 22, 2012 at 11:06 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>
>> We can use
>> pg_xlogfile_name function to calculate that, but it cannot be executed in
>> the standby. Another problem is that pg_xlogfile_name always uses
>> current timeline for the calculation, so if the reported timeline is not
>> the same as current one, pg_xlogfile_name cannot return the correct WAL
>> file name. Making pg_controldata report that WAL file name gets rid of
>> such a complexity.
>>
>
> i would think that pg_xlogfile_name() is not allowed in the standby
> because ThisTimelineId is not very well defined in recovery but if you
> extend pg_xlogfile_name() to also receive a timelineid as you
> suggested in [1] then that version of the function could be allowed in
> the standby.
> or there is something else i'm missing?
>
> is that enough for you to solve your problem?

Yes, we can more easily calculate the cutoff point by using that extended
pg_xlogfile_name(). But if pg_controldata reports the WAL file name, we
can calculate the cutoff point without starting the server. So I think that
it's worth changing pg_controldata that way even if we extend
pg_xlogfile_name().

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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Subject: Re: Reporting WAL file containing checkpoint's REDO record in pg_controldata's result
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