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

On Thu, Sep 11, 2014 at 9:59 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> With the exception of ExecChooseHashTableSize() and a lot of stylistic
>> issues along the lines of what I've already complained about, this
>> patch seems pretty good to me.  It does three things:
>> ...
>> (3) It allows the number of batches to increase on the fly while the
>> hash join is in process.  This case arises when we initially estimate
>> that we only need a small hash table, and then it turns out that there
>> are more tuples than we expect.  Without this code, the hash table's
>> load factor gets too high and things start to suck.
>
> 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.

-- 
Robert Haas
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