proposal 9.4. Explain on signal

Hello

I proposed a some months log plans of cancelled queries
http://www.postgresql.org/message-id/CAFj8pRA-DuzkmDtu52CiUgb0P7TVri_B8LtjMJfWcnr1LPts6w@mail.gmail.com
. After discussion the proposal was changed to get plan of any running
query.

I have a proof concept patch now and I am thinking so it can work well

So I propose following concept:

1. function pg_explain_backend(PID int, loglevel int default 'log',
explain_top_level boolean default true);

Execution of this function ensure sending sigusr1 signal to PID process.

2. Sigusr1 handler will be enhanced for PROCSIG_EXPLAIN_MESSAGES
message and it will write explain result to log.

It share lot of code with auto_explain module. So I am thinking so we
should move auto_explain functionality to core. Then EXPLAIN ON SIGNAL
can be used for monitoring of query evaluating.

Regards

Pavel

comments?