[pgpool-hackers: 3344] Reducing query issued by relcache

[Tatsuo Ishii]

Currently relcache module issues 7+ queries to obtain various info
from PostgreSQL system catalogs. Some of them are necessary for
Pgpool-II to work with multiple version of PostgreSQL.

Idea is, if we already know the version of PostgreSQL, we can
eliminate some of queries. For example, we need to know if
pg_namespace exists and for this purpose we send a query against
pg_class. But if we know that pg_namespace was introduced in
PostgreSQL 7.3, we do not need to inquire pg_class.

So I have created a patch to implement the idea.

In my testing with "select * from t1" issues 7 queries. After the
patch, it reduces to 3.

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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