pgsql: pgbench: When using pipelining only do PQconsumeInput() when nec

pgbench: When using pipelining only do PQconsumeInput() when necessary.

Up to now we did a PQconsumeInput() for each pipelined query, asking the OS
for more input - which it often won't have, as all results might already have
been sent. That turns out to have a noticeable performance impact.

Alvaro Herrera reviewed the idea to add the PQisBusy() check, but not this
concrete patch.

Author: Andres Freund <andres(at)anarazel(dot)de>
Discussion: https://postgr.es/m/20210720180039.23rivhdft3l4mayn@alap3.anarazel.de
Backpatch: 14, where libpq/pgbench pipelining was introduced.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/87bff68840d542011ed8f60427502fb90fdf2873

Modified Files
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src/bin/pgbench/pgbench.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)