pgsql: Improve performance of SendRowDescriptionMessage.

Andres Freund <andres@anarazel.de>

From: Andres Freund <andres@anarazel.de>

To: pgsql-committers@postgresql.org

Date: 2017-10-12T00:28:21Z

Lists: pgsql-hackers

Improve performance of SendRowDescriptionMessage.

There's three categories of changes leading to better performance:
- Splitting the per-attribute part of SendRowDescriptionMessage into a
  v2 and a v3 version allows avoiding branches for every attribute.
- Preallocating the size of the buffer to be big enough for all
  attributes and then using pq_write* avoids unnecessary buffer
  size checks & resizing.
- Reusing a persistently allocated StringInfo for all
  SendRowDescriptionMessage() invocations avoids repeated allocations
  & reallocations.

Author: Andres Freund
Discussion: https://postgr.es/m/20170914063418.sckdzgjfrsbekae4@alap3.anarazel.de

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/4c119fbcd49ba882791c7b99a1e934b985468e9f

Modified Files
--------------
src/backend/access/common/printtup.c | 146 ++++++++++++++++++++++++++---------
src/backend/tcop/postgres.c          |  35 +++++++--
src/include/access/printtup.h        |   4 +-
3 files changed, 138 insertions(+), 47 deletions(-)

Commits

Force "restrict" not to be used when compiling with xlc.
- d133982d598c 11.0 landed
Rely on sizeof(typename) rather than sizeof(variable) in pqformat.h.
- 5229db6c6f92 11.0 landed
Use C99 restrict via pg_restrict, rather than restrict directly.
- 91d5f1a4a3e8 11.0 cited
Improve performance of SendRowDescriptionMessage.
- 4c119fbcd49b 11.0 cited
Partially flatten struct tupleDesc so that it can be used in DSM.
- c6293249dc17 11.0 cited
Remove useless duplicate inclusions of system header files.
- 9e3755ecb2d0 10.0 cited