Re: Proposed Patch to Improve Performance of Multi-Batch Hash Join for Skewed Data Sets

On Wed, Nov 05, 2008 at 04:06:11PM -0800, Bryce Cutt wrote:
> The error is causes by me Asserting against the wrong variable.  I
> never noticed this as I apparently did not have assertions turned on
> on my development machine.  That is fixed now and with the new patch
> version I have attached all assertions are passing with your query and
> my test queries.  I added another assertion to that section of the
> code so that it is a bit more vigorous in confirming the hash table
> partition is correct.  It does not change the operation of the code.
>
> There are two partition counts.  One holds the maximum number of
> buckets in the hash table and the other counts the number of actual
> buckets created for hash values.  I was incorrectly testing against
> the second one because that was valid before I started using a hash
> table to store the buckets.
>
> The enable_hashjoin_usestatmcvs flag was valuable for my own research
> and tests and likely useful for your review but Tom is correct that it
> can be removed in the final version.
>
> - Bryce Cutt

Thanks for the new patch; I'll take a look as soon as I can (prolly
tomorrow).

- Josh