From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Jeff Davis <pgsql@j-davis.com>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: logtape.c stats don't account for unused "prefetched" block numbers
Date: Tue, 1 Sep 2020 19:36:02 -0400
Message-ID: <20200901233602.GA31048@alvherre.pgsql> (raw)
In-Reply-To: <CAH2-Wzn5PCBLUrrds=hD439LtWP+PD7ekRTd=8LdtqJ+KO5D1Q@mail.gmail.com>
On 2020-Jul-30, Peter Geoghegan wrote:
> Commit 896ddf9b added prefetching to logtape.c to avoid excessive
> fragmentation in the context of hash aggs that spill and have many
> batches/tapes. Apparently the preallocation doesn't actually perform
> any filesystem operations, so the new mechanism should be zero
> overhead when "preallocated" blocks aren't actually used after all
> (right?). However, I notice that this breaks the statistics shown by
> things like trace_sort, and even EXPLAIN ANALYZE.
> LogicalTapeSetBlocks() didn't get the memo about preallocation.
This open item hasn't received any replies. I think Peter knows how to
fix it already, but no patch has been posted ... It'd be good to get a
move on it.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: alvherre@2ndquadrant.com, pg@bowt.ie, pgsql@j-davis.com
Subject: Re: logtape.c stats don't account for unused "prefetched" block numbers
In-Reply-To: <20200901233602.GA31048@alvherre.pgsql>
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