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Re: Keeping separate WAL segments for each database

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Devrim GÜNDÜZ <devrim(at)gunduz(dot)org>, PostgreSQL Hackers ML <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Keeping separate WAL segments for each database
Date: 2010-07-03 11:02:40
Message-ID: AANLkTimSA_S8M4YWapNUJmuQMVjZq-YfGSQhKjRFot5s@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
2010/6/30 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> You need to make sure not only that you replay commit records in
>> order, but also that, for example, you don't replay an
>> XLOG_HEAP2_CLEAN record too early.
>
> Hm, good point.  That probably means that you *do* need fencepost
> records, and furthermore that you might need an interlock to ensure that
> you get the fencepost in early enough on the other stream.  Ugh ---
> there goes your concurrency.
>
> What about having a single WAL stream for all commit records (thereby
> avoiding any possible xact-serialization funnies) and other WAL records
> divided up among multiple streams in some fashion or other?  A commit
> record would bear minimum-LSN pointers for all the streams that its
> transaction had written to.  Things like HEAP_CLEAN records would bear
> minimum-LSN pointers for the commit stream.  Workable?

I don't see why not.  Of course, the performance of any of these ideas
is another question altogether...

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

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