From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Polyphase merge is obsolete
Date: Wed, 12 Oct 2016 13:27:25 -0400
Message-ID: <1162.1476293245@sss.pgh.pa.us> (raw)
In-Reply-To: <420a0ec7-602c-d406-1e75-1ef7ddc58d83@iki.fi>
References: <420a0ec7-602c-d406-1e75-1ef7ddc58d83@iki.fi>
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Heikki Linnakangas <hlinnaka@iki.fi> writes:
> The beauty of the polyphase merge algorithm is that it allows reusing
> input tapes as output tapes efficiently ... So the whole idea of trying to
> efficiently reuse input tapes as output tapes is pointless.
It's been awhile since I looked at that code, but I'm quite certain that
it *never* thought it was dealing with actual tapes. Rather, the point of
sticking with polyphase merge was that it allowed efficient incremental
re-use of temporary disk files, so that the maximum on-disk footprint was
only about equal to the volume of data to be sorted, rather than being a
multiple of that. Have we thrown that property away?
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, hlinnaka@iki.fi
Subject: Re: Polyphase merge is obsolete
In-Reply-To: <1162.1476293245@sss.pgh.pa.us>
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