Re: Hash Indexes - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Hash Indexes
Date
Msg-id 24404.1476812294@sss.pgh.pa.us
Whole thread Raw
In response to Re: Hash Indexes  (Robert Haas <robertmhaas@gmail.com>)
Responses Re: Hash Indexes  (Andres Freund <andres@anarazel.de>)
List pgsql-hackers
Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Oct 18, 2016 at 5:37 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> I have implemented this idea and it works for MVCC scans.  However, I
>> think this might not work for non-MVCC scans.  Consider a case where
>> in Process-1, hash scan has returned one row and before it could check
>> it's validity in heap, vacuum marks that tuple as dead and removed the
>> entry from heap and some new tuple has been placed at that offset in
>> heap.

> Oops, that's bad.

Do we care?  Under what circumstances would a hash index be used for a
non-MVCC scan?
        regards, tom lane



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