Horton

Re: SendRowDescriptionMessage() is slow for queries with a lot of columns

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: pgsql-hackers@postgresql.org
Date: 2017-10-03T07:55:22Z
Lists: pgsql-hackers

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Hi,

Attached is a revised version of this patchset. I'd like to get some
input on two points:

1) Does anybody have a better idea than the static buffer in
   SendRowDescriptionMessage()? That's not particularly pretty, but
   there's not really a convenient stringbuffer to use when called from
   exec_describe_portal_message(). We could instead create a local
   buffer for exec_describe_portal_message().

   An alternative idea would be to have one reeusable buffer created for
   each transaction command, but I'm not sure that's really better.

2) There's a lot of remaining pq_sendint() callers in other parts of the
   tree. If others are ok with that, I'd do a separate pass over them.
   I'd say that even after doing that, we should keep pq_sendint(),
   because a lot of extension code is using that.

3) The use of restrict, with a configure based fallback, is something
   we've not done before, but it's C99 and delivers significantly more
   efficient code. Any arguments against?

Regards,

Andres

Commits

  1. Replace remaining uses of pq_sendint with pq_sendint{8,16,32}.

  2. Improve performance of SendRowDescriptionMessage.

  3. Use one stringbuffer for all rows printed in printtup.c.

  4. Add configure infrastructure to detect support for C99's restrict.

  5. Add more efficient functions to pqformat API.

  6. Allow to avoid NUL-byte management for stringinfos and use in format.c.

  7. Replace most usages of ntoh[ls] and hton[sl] with pg_bswap.h.

  8. Extend & revamp pg_bswap.h infrastructure.