pgsql: Add a "row processor" API to libpq for better handling of large

Add a "row processor" API to libpq for better handling of large results.

Traditionally libpq has collected an entire query result before passing
it back to the application. That provides a simple and transactional API,
but it's pretty inefficient for large result sets. This patch allows the
application to process each row on-the-fly instead of accumulating the
rows into the PGresult. Error recovery becomes a bit more complex, but
often that tradeoff is well worth making.

Kyotaro Horiguchi, reviewed by Marko Kreen and Tom Lane

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/92785dac2ee7026948962cd61c4cd84a2d052772

Modified Files
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doc/src/sgml/libpq.sgml | 268 +++++++++++++++++++++++++++++
src/interfaces/libpq/exports.txt | 3 +
src/interfaces/libpq/fe-connect.c | 12 +-
src/interfaces/libpq/fe-exec.c | 177 ++++++++++++++++++-
src/interfaces/libpq/fe-lobj.c | 40 +++--
src/interfaces/libpq/fe-misc.c | 26 +++
src/interfaces/libpq/fe-protocol2.c | 325 ++++++++++++++++++++++++++---------
src/interfaces/libpq/fe-protocol3.c | 298 +++++++++++++++++++++++----------
src/interfaces/libpq/libpq-fe.h | 31 +++-
src/interfaces/libpq/libpq-int.h | 14 ++-
10 files changed, 992 insertions(+), 202 deletions(-)