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: Robert Haas <robertmhaas@gmail.com>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-10-11T03:19:42Z
Lists: pgsql-hackers

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Hi,

On 2017-10-03 13:58:37 -0400, Robert Haas wrote:
> On Tue, Oct 3, 2017 at 12:23 PM, Andres Freund <andres@anarazel.de> wrote:
> > Makes sense?
> 
> Yes.

Here's an updated version of this patchset. Changes:

- renamed pq_send$type_pre to pq_write*type
- renamed pq_beginmessage_pre/pq_beginmessage_keep to the _reuse suffix
- removed unaligned memory access issues by again using memcpy - gcc and
  clang both successfully optimize it away
- moved permanent buffer for SendRowDescriptionMessage to postgres.c,
  and have other callers use already pre-existing buffers.
- replace all pq_sendint with pq_sendint$width in core
- converted applicable pq_begin/endmessage in printtup.c users to use
  DR_printtup->buf.
- added comments explaining restrict usage
- expanded commit messages considerably
- Small stuff.

The naming I'd discussed a bit back and forth with Robert over IM,
thanks!

- 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.