> > This also brings up a line of thought I had a while ago on a related
> > topic. Something like a "HashDistinct" might be useful, if it had no
> > startup cost.
> We already have that: the planner will use a HashAgg node in this
> fashion in some contexts (I think just as one of the ways to
Bruno Wolff III <[EMAIL PROTECTED]> writes:
> Tom Lane <[EMAIL PROTECTED]> wrote:
>> Bruno Wolff III <[EMAIL PROTECTED]> writes:
>>> If K is way low this could be very slow.
>>
>> How so? You're not concerned about the time to do the division itself
>> are you?
> No, rather having lots of entrie
On Fri, Mar 04, 2005 at 10:42:08 -0500,
Tom Lane <[EMAIL PROTECTED]> wrote:
> Bruno Wolff III <[EMAIL PROTECTED]> writes:
> > Tom Lane <[EMAIL PROTECTED]> wrote:
> >> * Estimate the number of batches N using the planner's estimate.
> >> We will always choose N a power of 2. A tuple's batch num
Bruno Wolff III <[EMAIL PROTECTED]> writes:
> Tom Lane <[EMAIL PROTECTED]> wrote:
>> * Estimate the number of batches N using the planner's estimate.
>> We will always choose N a power of 2. A tuple's batch number is
>> ((H div K) mod N).
> If K is way low this could be very slow.
How so? You
On Thu, Mar 03, 2005 at 17:05:40 -0500,
Tom Lane <[EMAIL PROTECTED]> wrote:
>
> * Estimate the number of batches N using the planner's estimate.
> We will always choose N a power of 2. A tuple's batch number is
> ((H div K) mod N).
If K is way low this could be very slow. Is there a way to do
Aaron Birkland <[EMAIL PROTECTED]> writes:
> This also brings up a line of thought I had a while ago on a related
> topic. Something like a "HashDistinct" might be useful, if it had no
> startup cost. It would basically be a plan node in the executor that
> would dynamically build a hashtable so
> We saw a case recently where a hash join was using much more memory than
> it was supposed to, causing failure when the server ran out of memory.
Yes. I had the same problem a few month ago,
http://archives.postgresql.org/pgsql-general/2004-09/msg00410.php
It turned out that the cost estimates
