Thread: Disk usage for intermediate results in join

On 03/11/2014 01:24 PM, Parul Lakkad wrote:
> Hi,
>
> I am trying to figure out when disk is used to store intermediate results
> while performing joins in postgres.
>
> According my findings using 'explain analyse ' only merge sort uses disk.
> Can anyone please throw some more light on this?

Hash joins will also spill to disk if the hash-side of the join is large 
enough. The planner usually tries to avoid it, but sometimes it happens.

- Heikki

On Tue, Mar 11, 2014 at 1:24 PM, Parul Lakkad <parul.lakkad@gmail.com> wrote:
> I am trying to figure out when disk is used to store intermediate results
> while performing joins in postgres.

Joins can also cause a Nested Loop+Materialize plan, which spills to
disk if the materialize result set is too large for work_mem.

Regards,
Marti