From: | Jan Wieck <JanWieck(at)Yahoo(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Simon Riggs <simon(at)2ndQuadrant(dot)com>, PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Exposing the Xact commit order to the user |
Date: | 2010-06-01 15:06:05 |
Message-ID: | 4C0521DD.40806@Yahoo.com |
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Thread: | |
Lists: | pgsql-hackers |
On 5/28/2010 7:19 PM, Bruce Momjian wrote:
> Jan Wieck wrote:
>> >> Reading the entire WAL just to find all COMMIT records, then go back to
>> >> the origin database to get the actual replication log you're looking for
>> >> is simpler and more efficient? I don't think so.
>> >
>> > Agreed, but I think I've not explained myself well enough.
>> >
>> > I proposed two completely separate ideas; the first one was this:
>> >
>> > If you must get commit order, get it from WAL on *origin*, using exact
>> > same code that current WALSender provides, plus some logic to read
>> > through the WAL records and extract commit/aborts. That seems much
>> > simpler than the proposal you outlined and as SR shows, its low latency
>> > as well since commits write to WAL. No need to generate event ticks
>> > either, just use XLogRecPtrs as WALSender already does.
>> >
>> > I see no problem with integrating that into core, technically or
>> > philosophically.
>> >
>>
>> Which means that if I want to allow a consumer of that commit order data
>> to go offline for three days or so to replicate the 5 requested, low
>> volume tables, the origin needs to hang on to the entire WAL log from
>> all 100 other high volume tables?
>
> I suggest writing an external tool that strips out what you need that
> can be run at any time, rather than creating a new data format and
> overhead for this usecase.
>
Stripping it out from what?
Jan
--
Anyone who trades liberty for security deserves neither
liberty nor security. -- Benjamin Franklin
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