Subject: Re: GiST VACUUM
To: Andrey Borodin <x4mmm@yandex-team.ru>
Cc: Michael Paquier <michael@paquier.xyz>,
 Thomas Munro <thomas.munro@enterprisedb.com>,
 Robert Haas <robertmhaas@gmail.com>,
 pgsql-hackers <pgsql-hackers@postgresql.org>,
 =?UTF-8?B?0JrQvtGB0YLRjyDQmtGD0LfQvdC10YbQvtCy?= <chapaev28@ya.ru>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
Message-ID: <8663c730-0895-cf80-acc2-e7149f6455e6@iki.fi>
Date: Fri, 22 Mar 2019 12:28:53 +0200
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On 22/03/2019 10:00, Andrey Borodin wrote:
>> 22 марта 2019 г., в 1:04, Heikki Linnakangas <hlinnaka@iki.fi>
>> написал(а):
>>
>> PS. for Gist, we could almost use the LSN / NSN mechanism to detect
>> the case that a deleted page is reused: Add a new field to the GiST
>> page header, to store a new "deleteNSN" field. When a page is
>> deleted, the deleted page's deleteNSN is set to the LSN of the
>> deletion record. When the page is reused, the deleteNSN field is
>> kept unchanged. When you follow a downlink during search, if you
>> see that the page's deleteNSN > parent's LSN, you know that it was
>> concurrently deleted and recycled, and should be ignored. That
>> would allow reusing deleted pages immediately. Unfortunately that
>> would require adding a new field to the gist page header/footer,
>> which requires upgrade work :-(. Maybe one day, we'll bite the
>> bullet. Something to keep in mind, if we have to change the page
>> format anyway, for some reason.
>
> Yeah, the same day we will get rid of invalid tuples. I can make a
> patch for v13. Actually, I have a lot of patches that I want in GiST
> in v13. Or v14.

Cool! Here's my wishlist:

* That deleteNSN thing
* Add a metapage to blk #0.
* Add a "level"-field to page header.
* Currently, a search needs to scan all items on a page. If the keys are 
small, that can be pretty slow. Divide each page further into e.g. 4 
sub-pages, with a "bounding box" key for each sub-page, to speed up search.

- Heikki