Horton

Re: improve performance of pg_dump with many sequences

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>, Euler Taveira <euler@eulerto.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2024-07-18T03:45:32Z
Lists: pgsql-hackers

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Here is an attempt at adding a new function that returns the sequence tuple
and using that to avoid querying each sequence relation individually in
dumpSequenceData().

If we instead wanted to change pg_sequence_last_value() to return both
is_called and last_value, I think we could modify the pg_sequences system
view to use a LATERAL subquery, i.e.,

    SELECT
        ...
        CASE
            WHEN L.is_called THEN L.last_value
            ELSE NULL
        END AS last_value
    FROM pg_sequence S
        ...
        JOIN LATERAL pg_sequence_last_value(S.seqrelid) L ON true
    ...

That doesn't seem so bad, and it'd avoid an extra pg_proc entry, but it
would probably break anything that calls pg_sequence_last_value() directly.
Thoughts?

-- 
nathan

Commits

  1. pg_dump: Fix gathering of sequence information.

  2. Improve performance of dumpSequence().

  3. Improve performance of dumpSequenceData().

  4. Introduce pg_sequence_read_tuple().

  5. Parse sequence type and integer metadata in dumpSequence().