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(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)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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