Horton

Re: Hash Indexes

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Jesper Pedersen <jesper.pedersen@redhat.com>, Jeff Janes <jeff.janes@gmail.com>, Mithun Cy <mithun.cy@enterprisedb.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-10-18T17:38:14Z
Lists: 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

Commits

  1. Remove _hash_wrtbuf() in favor of calling MarkBufferDirty().

  2. Fix race introduced by 6d46f4783efe457f74816a75173eb23ed8930020.

  3. Improve hash index bucket split behavior.

  4. Reduce pinning and buffer content locking for btree scans.