Horton

Re: Yet another fast GiST build

Heikki Linnakangas <hlinnaka@iki.fi>

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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Peter Geoghegan <pg@bowt.ie>, Tom Lane <tgl@sss.pgh.pa.us>, Justin Pryzby <pryzby@telsasoft.com>, Darafei Komяpa Praliaskouski <me@komzpa.net>, Pavel Borisov <pashkin.elfe@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Michael Paquier <michael@paquier.xyz>, Alexander Korotkov <a.korotkov@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, Ibrar Ahmed <ibrar.ahmad@gmail.com>
Date: 2021-04-07T10:23:42Z
Lists: pgsql-hackers 
On 07/04/2021 09:00, Heikki Linnakangas wrote:
> On 08/03/2021 19:06, Andrey Borodin wrote:
>> There were numerous GiST-build-related patches in this thread. Yet uncommitted is a patch with sortsupport routines for btree_gist contrib module.
>> Here's its version which needs review.

Committed with small fixes. I changed the all functions to use 
*GetDatum() and DatumGet*() macros, instead of just comparing Datums 
with < and >. Datum is unsigned, while int2, int4, int8 and money are 
signed, so that changes the sort order around 0 for those types to be 
the same as the picksplit and picksplit functions use. Not a correctness 
issue, the sorting only affects the quality of the index, but let's be tidy.

This issue remains:

> Reviewing this now again. One thing caught my eye:
> 
>> +static int
>> +gbt_bit_sort_build_cmp(Datum a, Datum b, SortSupport ssup)
>> +{
>> +	return DatumGetInt32(DirectFunctionCall2(byteacmp,
>> +											 PointerGetDatum(a),
>> +											 PointerGetDatum(b)));
>> +}
> 
> That doesn't quite match the sort order used by the comparison
> functions, gbt_bitlt and such. The comparison functions compare the bits
> first, and use the length as a tie-breaker. Using byteacmp() will
> compare the "bit length" first. However, gbt_bitcmp() also uses
> byteacmp(), so I'm a bit confused. So, huh?

Since we used byteacmp() previously for picksplit, too, this is 
consistent with the order you got previously. It still seems wrong to me 
and should be investigated, but it doesn't need to block this patch.

- Heikki

Commits

  1. Add sortsupport for gist_btree opclasses, for faster index builds.

  2. pageinspect: Fix relcache leak in gist_page_items().

  3. Fix test failure with wal_level=minimal.

  4. Enhance nbtree index tuple deletion.

  5. Fix portability issues in the new gist pageinspect test.

  6. Add functions to 'pageinspect' to inspect GiST indexes.

  7. Fix missing validation for the new GiST sortsupport functions.

  8. Fix compilation warning in xlog.c

  9. Set right-links during sorted GiST index build.

  10. Fix checksum calculation in the new sorting GiST build.

  11. Add support for building GiST index by sorting.