Re: Hash join in SELECT target list expression keeps consuming memory

On 17 March 2018 at 00:47, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> writes:
>> If the SELECT target list expression is a join subquery, and if the
>> subquery does a hash join, then the query keeps on consuming more and
>> more memory. Below is such a query :
>
> Thanks for the report!
>
> I dug into this with valgrind, and found that the problem is that
> ExecHashTableCreate allocates some memory that isn't freed by
> ExecHashTableDestroy, specifically the per-hash-key function
> information. This is just dumb. We can keep that stuff in the
> hashtable's hashCxt instead, where it will get freed at the right time.
> The attached patch seems to fix it just by reordering the code.

I saw that you have now committed the fix and also backported it to
all supported branches.

Thanks !

-Amit Khandekar
EnterpriseDB Corporation
The Postgres Database Company