Re: bad estimation together with large work_mem generates terrible slow hash joins

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Sep 11, 2014 at 9:59 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Robert Haas <robertmhaas@gmail.com> writes:
>>> (3) It allows the number of batches to increase on the fly while the
>>> hash join is in process.

>> Pardon me for not having read the patch yet, but what part of (3)
>> wasn't there already?

> EINSUFFICIENTCAFFEINE.

> It allows the number of BUCKETS to increase, not the number of
> batches.  As you say, the number of batches could already increase.

Ah.  Well, that would mean that we need a heuristic for deciding when to
increase the number of buckets versus the number of batches ... seems
like a difficult decision.
        regards, tom lane