pgsql: Rearm statement_timeout after each executed query.

Rearm statement_timeout after each executed query.

Previously statement_timeout, in the extended protocol, affected all
messages till a Sync message.  For clients that pipeline/batch query
execution that's problematic.

Instead disable timeout after each Execute message, and enable, if
necessary, the timer in start_xact_command(). As that's done only for
Execute and not Parse / Bind, pipelining the latter two could still
cause undesirable timeouts. But a survey of protocol implementations
shows that all drivers issue Sync messages when preparing, and adding
timeout rearming to both is fairly expensive for the common parse /
bind / execute sequence.

Author: Tatsuo Ishii, editorialized by Andres Freund
Reviewed-By: Takayuki Tsunakawa, Andres Freund
Discussion: https://postgr.es/m/20170222.115044.1665674502985097185.t-ishii@sraoss.co.jp

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f8e5f156b30efee5d0038b03e38735773abcb7ed

Modified Files
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src/backend/tcop/postgres.c | 77 ++++++++++++++++++++++++++++++++++++++-------
1 file changed, 65 insertions(+), 12 deletions(-)