[pgpool-hackers: 3844] Preventing sending sync message to standby

[Tatsuo Ishii]

Currently Pgpool-II forwards sync messages to all backends. This is
usually harmless but if one of standby servers are located at distant
place, the network delay affected the performance of Pgpool-II as it
must wait for responses ("ready for query" message from backend) from
all backends including the distant server. For such that cross
Continental configuration, it would be nice if the distant backend's
weight to be set to 0 and the sync message is not send to such a
standby. Attached patch tries to implement that. It records whether
Pgpool-II has sent any message to each backend in
query_issued_since_last_sync map. When a sync message comes from
frontend, Pgpool-II looks in to the map and sends to the only backend
which has a record in the map. Unfortunately after patching it,
Pgpool-II's performance is degraded ~10% using pgbench -S and I gave
up to apply it. I hope someone tests the patch and finds out what is
wrong with it.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
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