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Re: incorrect handling of the timeout in pg_receivexlog

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: incorrect handling of the timeout in pg_receivexlog
Date: 2012-03-29 04:43:49
Message-ID: CAHGQGwFToYdUP1RP9PpKW7W=y=VhffMWawpMMTX4=aPTJ9NZMg@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, Feb 28, 2012 at 6:08 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Wed, Feb 8, 2012 at 1:33 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
>> Will it break using pg_basebackup 9.2 on a 9.1 server, though? that
>> would also be very useful in the scenario of the central server...
>
> No unless I'm missing something. Because pg_basebackup doesn't use
> any message which is defined in walprotocol.h if "-x stream" option is
> not specified.

No, this is not right at all :( Changing TimestampTz fields in 9.2 would break
that use case.

If we support that use case, pg_basebackup 9.2 must know which an integer
or a double is used for TimestampTz in 9.1 server. Otherwise pg_basebackup
cannot process a WAL data message proporly. But unfortunately there is no
way for pg_basebackup 9.2 to know that... 9.1 has no API to report the actual
datatype of its TimestampTz field.

One idea to support that use case is to add new command-line option into
pg_basebackup, which specifies the datatype of TimestampTz field. You can
use one pg_basebackup 9.2 executable on 9.1 server whether
--disable-integer-datetimes is specified or not. But I'm not really sure if it's
worth doing this, because ISTM that it's rare to build a server and a
client with
the different choice about TimestampTz datatype.

Regards,

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

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