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: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-10-11T22:04:02Z
Lists: pgsql-hackers 
On 2017-10-11 08:54:10 -0700, Andres Freund wrote:
> On 2017-10-11 10:53:56 +0200, Alvaro Herrera wrote:
> > Maybe it'd be a good idea to push 0001 with some user of restrict ahead
> > of the rest, just to see how older msvc reacts.
> 
> Can do. Not quite sure which older user yet, but I'm sure I can find
> something.

I looked around and didn't immedialy see a point where it'd be useful. I
don't really want to put it in some place where it's not useful. I think
we can just as well wait for the first patch using it to exercise
restrict support.

There's references to restrict support back to VS 2008:
https://msdn.microsoft.com/en-us/library/5ft82fed(v=vs.90).aspx


So I'll change the pg_config.h.win32 hunk to:
/* Define to the equivalent of the C99 'restrict' keyword, or to
   nothing if this is not supported.  Do not define if restrict is
   supported directly.  */
/* Visual Studio 2008 and upwards */
#if (_MSC_VER >= 1500)
/* works for C and C++ in msvc */
#define restrict __restrict
#else
#define restrict
#endif

there's several patterns like that (except for the version mapping) in
the file already.

- 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.