From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Sam Mason <sam(at)samason(dot)me(dot)uk> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Polyphase Merge |
Date: | 2008-01-21 21:13:32 |
Message-ID: | 18768.1200950012@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Sam Mason <sam(at)samason(dot)me(dot)uk> writes:
> It's really up to you to find answers to these questions, especially
> the first one. Once you've designed an efficient algorithm then the
> second point (which I'm interpreting as how you'd go about changing
> tuplestore(?) so that things can be read in reverse order) should
> just drop out as an implementation detail :) I'm guessing you'll
> end up not reading the store in reverse order but arranging things
> differently---it'll be interesting to see.
I agree --- having to read the run back from external storage, only to
write it out again with no further useful work done on it, sounds like
a guaranteed loser. To make this work you'll need some kind of ju-jitsu
rearrangement that logically puts the run where it needs to go without
physically moving any data.
regards, tom lane
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