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Thread: HASH

HASH

From

Artem Tomyuk

Date:

05 November 2015, 12:11:36

Hi all.

Is the speed of hash operations stands on the performance of CPU?

Below you can see part from output of explain analyze command

Intel(R) Xeon(R) CPU E7520 @ 1.87GHz

" -> Hash (cost=337389.43..337389.43 rows=3224443 width=34) (actual time=15046.382..15046.382 rows=3225191 loops=1)"

" Buckets: 524288 Batches: 1 Memory Usage: 207874kB"

Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz

" -> Hash (cost=340758.94..340758.94 rows=3191894 width=34) (actual time=2692.878..2692.878 rows=3192103 loops=1)"

" Buckets: 524288 Batches: 1 Memory Usage: 205742kB"

Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz" -> Hash (cost=337389.43..337389.43 rows=3224443 width=34) (actual time=8559.849..8559.849 rows=3225293 loops=1)"
" Buckets: 524288 Batches: 1 Memory Usage: 207881kB"

Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz

" -> Hash (cost=356613.23..356613.23 rows=3224623 width=40) (actual time=3635.931..3635.931 rows=3224623 loops=1)"

" Buckets: 524288 Batches: 1 Memory Usage: 207838kB"

Thanks.

Re: HASH

From

Jeff Janes

Date:

05 November 2015, 14:24:34

On Thu, Nov 5, 2015 at 1:11 AM, Artem Tomyuk <admin@leboutique.com> wrote:
> Hi all.
>
> Is the speed of hash operations stands on the performance of CPU?

Yes, but the variation is probably not as much as the raw timing in
your example indicates.

> Below you can see part from output of explain analyze command
>
> Intel(R) Xeon(R) CPU           E7520  @ 1.87GHz
>
> "              ->  Hash  (cost=337389.43..337389.43 rows=3224443 width=34)
> (actual time=15046.382..15046.382 rows=3225191 loops=1)"
> "                    Buckets: 524288  Batches: 1  Memory Usage: 207874kB"

A lot of that time was probably spent reading the data off of disk so
that it could hash it.

You should turn track_io_timing on, run "explain (analyze, buffers)
..." and then show the entire explain output, or at least also show
the entries downstream of the Hash node.

Cheers,

Jeff