Re: avoiding tuple copying in btree index builds

Hi,

On 2014-05-05 13:52:39 -0400, Robert Haas wrote:
> Today, I discovered that when building a btree index, the btree code
> uses index_form_tuple() to create an index tuple from the heap tuple,
> calls tuplesort_putindextuple() to copy that tuple into the sort's
> memory context, and then frees the original one it built.  This seemed
> inefficient, so I wrote a patch to eliminate the tuple copying.  It
> works by adding a function tuplesort_putindextuplevalues(), which
> builds the tuple in the sort's memory context and thus avoids the need
> for a separate copy.  I'm not sure if that's the best approach, but
> the optimization seems wortwhile.

Hm. It looks like we could quite easily just get rid of
tuplesort_putindextuple(). The hash usage doesn't look hard to convert.

> I tested it by repeatedly executing "REINDEX INDEX
> pgbench_accounts_pkey" on a PPC64 machine.  pgbench_accounts contains
> 10 million records.  With unpatched master as of
> b2f7bd72c4d3e80065725c72e85778d5f4bdfd4a, I got times of 6.159s,
> 6.177s, and 6.201s.  With the attached patch, I got times of 5.787s,
> 5.972s, and 5.913s, a savings of almost 5%.  Not bad considering the
> amount of work involved.

Yes, that's certainly worthwile. Nice.

Greetings,

Andres Freund

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