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Re: Keeping separate WAL segments for each database

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
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: 2010-07-01 02:21:52
Message-ID: 22475.1277950912@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
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?

			regards, tom lane

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