pgbench post-connection command

New -x option for pgbench executes the given command once after
connection of each session.

e.g.
pgbench -x "SET synchronous_commit = off"
pgbench -x "SET foo_extension.enabled = on"

Allows easier testing of user parameters. Command listed in final report

$ pgbench -c 2 -t 4 -x "set synchronous_commit = off"
starting vacuum...end.
transaction type: TPC-B (sort of)
post connect command: [set synchronous_commit = off]
scaling factor: 1
query mode: simple
number of clients: 2
number of threads: 1
number of transactions per client: 4
number of transactions actually processed: 8/8
tps = 122.897304 (including connections establishing)
tps = 179.953212 (excluding connections establishing)

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services