Horton

Re: Optimize partial TOAST decompression

Binguo Bao <djydewang@gmail.com>

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From: Binguo Bao <djydewang@gmail.com>
To: Paul Ramsey <pramsey@cleverelephant.ca>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>, Pgsql Hackers <pgsql-hackers@postgresql.org>
Date: 2019-07-03T16:06:13Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Properly determine length for on-disk TOAST values

  2. Blind attempt to fix pglz_maximum_compressed_size

  3. Optimize partial TOAST decompression

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Paul Ramsey <pramsey@cleverelephant.ca> 于2019年7月2日周二 下午10:46写道：

> This looks good to me. A little commentary around why
> pglz_maximum_compressed_size() returns a universally correct answer
> (there's no way the compressed size can ever be larger than this
> because...) would be nice for peasants like myself.
>
> If you're looking to continue down this code line in your next patch,
> the next TODO item is a little more involved: a user-land (ala
> PG_DETOAST_DATUM) iterator API for access of TOAST datums would allow
> the optimization of searching of large objects like JSONB types, and
> so on, where the thing you are looking for is not at a known location
> in the object. So, things like looking for a particular substring in a
> string, or looking for a particular key in a JSONB. "Iterate until you
> find the thing." would allow optimization of some code lines that
> currently require full decompression of the objects.
>
> P.
>

Thanks for your comment. I've updated the patch.
As for the iterator API, I've implemented a de-TOAST iterator actually[0].
And I’m looking for more of its application scenarios and perfecting it.
Any comments would be much appreciated.

Best Regards, Binguo Bao.

[0]
https://www.postgresql.org/message-id/flat/CAL-OGks_onzpc9M9bXPCztMofWULcFkyeCeKiAgXzwRL8kXiag@mail.gmail.com