Thread: backend crashes with mnogosearch

hi postgres-team,

i have set up a the mnogosearch engine on our webserver using postgresql
version 7.0.2. in the last time i experienced server errors when searching
for certain keywords. it turned out that the problem was the database
crashing on certain select statements on the mnogosearch url table.

further investigatoin showed that a simple "SELECT * FROM url" query
resulted in

Backend message type 0x44 arrived while idle
pqReadData() -- backend closed the channel unexpectedly.
        This probably means the backend terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.

then i tried several "SELECT * FROM url LIMIT <some number>" queries.
up to a certain number the queries were successful, but from that
number on i got the error message.

i thought about upgrading to postgresql 7.0.3, but since i expect
version 7.1 to be released soon, i decided to wait until then.

i know this is probably not enough information for you to tell me
what is the problem exactly, but maybe you have a quick work-around.

thanks,

nick wellnhofer

Nick Wellnhofer <nick@paradigmashift.com> writes:
> further investigatoin showed that a simple "SELECT * FROM url" query
> resulted in

> Backend message type 0x44 arrived while idle
> pqReadData() -- backend closed the channel unexpectedly.

Are you sure this is a backend crash?  (Real proof would be a report
of abnormal child termination in the postmaster's log, or appearance
of a core dump file in the database's subdirectory.)  The "arrived while
idle" bit looks suspiciously like the sort of misbehavior that libpq
tends to engage in if it runs out of memory for a query result.

> then i tried several "SELECT * FROM url LIMIT <some number>" queries.
> up to a certain number the queries were successful, but from that
> number on i got the error message.

How big is the "certain number", and how close might that number of
rows come to exhausting your frontend application's available memory?

            regards, tom lane