[Pgpool-hackers] Invalidating relcache

[Tatsuo Ishii]

Hi,

Pgpool-II maintaines internal relation cache to caching the query
result against backend. The cache scope is per session i.e. existing
in pgpool child process. The cache is mainly used for inquring system
catalog to know if the table is a tempory one, or rewirting timestamp
for example. Problem is, if the structure of a table which is in the
cache is changed by ALTER TABLE ADD COLUMN or some such, the contents
of the relcache are not valid anymore.

The only solution at present is, restarting pgpool or using
child_life_time, not super conveninet.

My idea is adding an expiration timer in the cache entry so that the
cache entry is invalidated after N seconds. The N can be changed by
editing pgpool.conf.

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