Re: function side effects

> > I'm wondering if we could detect a funcion has a side effect,
> > i.e. does a write to database. This is neccessary for pgpool to decide
> > if a qeury should to be sent to all of databases or not. If a query
> > includes functions which do writes to database, it should send the
> > query to all of databases, otherwise the contents of databases go into
> > inconsistent state.
> > 
> > Currently we have three properties of functions: IMMUTABLE, STABLE and
> > VOLATILE. According to docs IMMUTABLE or STABLE functions do not write
> > to database. VOLATILE functions *may* do writes to database. Maybe I
> > could regard VOLATILE functions always do write, but priblem is,
> > VOLATILE qfunctions such as random() and timeofday() apparently do not
> > write and sending those queries that include such functions is
> > overkill.
> > 
> > Can we VOLATILE property divide into two categories, say, VOLATILE
> > without write, and VOLATILE with write?
> 
> pgpool parses the query before deciding how to route it, yes?

Right.

> Why not mark random() and timeofday() as stable in the pgpool catalog,
> yet leave them as volatile on the database servers? It will "just work"
> then.

Please note that random() and timeofday() are just examples. What I'm
thinking about was, a function which directly or indirectly cause
write to database (thus lead writing to log).

Consider a function that calls those has-side-effect functions. We
need a property which is inherited to child function to parent
function.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp