Re: Extension to rewrite queries before execution

> I am looking for an extension or a technique that will allow me to
> intercept a query by the exact query text, and replace that query with a
> different one.
>
> The context is running a third-party app which issues queries I have no
> control over.  I'd like to intercept a specific query (which has no bind
> parameters) and either replace the query text with a different text which,
> for example, swaps out an "in list" clause to instead be an "exists
> (subquery)".
>
> Or just wrap the query in a "set enable_* =off;" or "set work_mem=*;"
> before and a reset of it after.
>
> Is there anything out there like this?  This would be for 9.4.
>
> I'm willing to put the query text, and its replacement, directly into the
> extension source code and compile it, but of course something more flexible
> would be ideal.

I don't know if you are interested in using other than extensions, but
you could do it by hacking pgpool-II. It has built-in raw parser with
some functions to walk through the tree such as
raw_expression_tree_walker().  Also you could do the rewriting only
for particular applications (of course only if the application set
application name).

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