Horton

Re: GiST VACUUM

x4mmm@yandex-team.ru

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From: Andrey Borodin <x4mmm@yandex-team.ru>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>, Robert Haas <robertmhaas@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Костя Кузнецов <chapaev28@ya.ru>
Date: 2018-08-06T18:12:00Z
Lists: pgsql-hackers

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Hi!

PFA v16.

> 5 авг. 2018 г., в 21:45, Andrey Borodin <x4mmm@yandex-team.ru> написал(а):
>> 5 авг. 2018 г., в 16:18, Heikki Linnakangas <hlinnaka@iki.fi> написал(а):
>> 
>> Hmm. A ListCell is 16 bytes, plus the AllocChunk header, 16 bytes. 32
>> bytes per internal page in total, while a bitmap consumes one bit per page, leaf or internal. If I'm doing
>> my math right, assuming the ratio of leaf pages vs internal pages is
>> 1:200, a List actually consumes more memory than a bitmap; 256 bits per
>> internal page, vs. 200 bits. An array, with 4 bytes per block number,
>> would be the winner here.
> We do not know size of this array beforehand. I can implement normal ArrayList though (with repallocing array) or linked list of chunks. Or anything from data structures zoo.
> Or just stick with bitmap (my preferred way).
Done.
>> 
>>> But I have to note that default growth strategy of Bitmap is not good: we will be repallocing byte by byte.
>> 
>> True, that repallocing seems bad. You could force it to be pre-allocated
>> by setting the last bit. Or add a function to explicitly enlarge the bitmap.
> OK, I'll think of proper resize function (ensure capacity, to be precise).
Done. Added function bms_make_empty(int size)

Best regards, Andrey Borodin.

Commits

  1. Use full 64-bit XID for checking if a deleted GiST page is old enough.

  2. Refactor checks for deleted GiST pages.

  3. Delete empty pages during GiST VACUUM.

  4. Scan GiST indexes in physical order during VACUUM.

  5. Prevent GIN deleted pages from being reclaimed too early