Postgres 6.3 Hash Tables

Howdy!

This may be a bug and may just be a problem on my side...
don't know.

When doing a query using 5 tables that has a query plan using
hashes and hash joins, I sometimes get this message:

"java.sql.SQLException: ERROR:  hash table out of memory.
Use -B parameter to increase buffers."

I'm assuming the "-B" option refers to the postmaster command
and I increased it from the default of 64 to 90.  (Any higher and I
get a postmaster error message.)

But the most confusing part, I can do the 5 table queries at times.
Then, all of a sudden, it stops.  No database changes.  Works one
minutes, fails the next, and I'm not sure how to get it going again.
I tried killing all postmaster, postgres, and psql processes and
starting over, but once it's broken, I'm not sure what to do to
fix it.

Is there some sort of cleanup that I need to do after each query?  Is
there a memory leak in the hash tables?  Better indexing?

Any help is appreciated.

John