How to know a table has been modified?

I'm working on implementing query cache in pgpool-II. I want to know
if a table has been modified because pgpool-II has to invalidate cache
if corresponding table is modified. For DDL/DML it would be doable
since pgpool-II knows all SQLs sent from clients. Problem is, implicit
table modifications done by CASCADE, TRIGGERS and so on.

create table t1(i int, j int);
create table t2(i int references t1.i);
drop table t1 cascade;

In this example, if t1 is dropped, t2 is dropped as well. So query
cache corresponding to t1 and t2 should be invalidated. The only way I
could thinking of is, looking into pg_depend. I would like to know if
there's any better/convenient way to know it.

For TRIGGER, I cannot thinking of any way. Any idea will be welcome.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

Tatsuo Ishii <ishii(at)postgresql(dot)org> writes:
> I'm working on implementing query cache in pgpool-II. I want to know
> if a table has been modified because pgpool-II has to invalidate cache
> if corresponding table is modified. For DDL/DML it would be doable
> since pgpool-II knows all SQLs sent from clients. Problem is, implicit
> table modifications done by CASCADE, TRIGGERS and so on.

Some of that (triggers) is provided in the command triggers patch. The
CASCADE not so much but your command trigger will get called on the
top-level object.

Regards,
--
Dimitri Fontaine
http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support