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Re: logtape.c stats don't account for unused "prefetched" block numbers - Mailing list pgsql-hackers

From Peter Geoghegan
Subject Re: logtape.c stats don't account for unused "prefetched" block numbers
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Msg-id CAH2-Wzn2PhgQNc9k+N3KHz=mRehmR0OmsGYPEsEQcfqDzdNQUQ@mail.gmail.com
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In response to Re: logtape.c stats don't account for unused "prefetched" block numbers  (Peter Geoghegan <pg@bowt.ie>)
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On Mon, Sep 14, 2020 at 3:39 PM Peter Geoghegan <pg@bowt.ie> wrote:
> I think that they are an exact match in practice (i.e. nBlocksWritten
> == nBlocksAllocated), given when and how we call
> LogicalTapeSetBlocks().

Just to be clear: this is only true for external sorts. The
preallocation stuff can make nBlocksAllocated quite a lot higher.
That's probably why adding a new "Assert(lts->nBlocksWritten ==
lts->nBlocksAllocated)" assertion fails during the regression tests,
though there might be other reasons as well (I'm thinking of the
LogicalTapeRewindForRead() inconsistency Jeff mentioned).

-- 
Peter Geoghegan

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