Horton

Re: Hash Indexes

Oskari Saarenmaa <os@ohmu.fi>

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From: Oskari Saarenmaa <os@ohmu.fi>
To: Robert Haas <robertmhaas@gmail.com>, Bruce Momjian <bruce@momjian.us>
Cc: Andres Freund <andres@anarazel.de>, Jeff Janes <jeff.janes@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2016-09-21T16:49:15Z
Lists: pgsql-hackers 
21.09.2016, 15:29, Robert Haas kirjoitti:
> For PostgreSQL, I expect the benefits of improving hash indexes to be
> (1) slightly better raw performance for equality comparisons and (2)
> better concurrency.

There's a third benefit: with large columns a hash index is a lot 
smaller on disk than a btree index.  This is the biggest reason I've 
seen people want to use hash indexes instead of btrees.  hashtext() 
btrees are a workaround, but they require all queries to be adjusted 
which is a pain.

/ Oskari

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.