| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Taylor Vesely <tvesely(at)pivotal(dot)io>, Adam Lee <ali(at)pivotal(dot)io>, Melanie Plageman <mplageman(at)pivotal(dot)io>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Memory-Bounded Hash Aggregation |
| Date: | 2019-12-27 23:35:30 |
| Message-ID: | d72e494db7b075ef02c3163e6614e698701d2c3e.camel@j-davis.com |
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| Lists: | pgsql-hackers |
On Sat, 2019-12-14 at 18:32 +0100, Tomas Vondra wrote:
> So I think we're not costing the batching properly / at all.
Hi,
I've attached a new patch that adds some basic costing for disk during
hashagg.
The accuracy is unfortunately not great, especially at smaller work_mem
sizes and smaller entry sizes. The biggest discrepency seems to be the
estimate for the average size of an entry in the hash table is
significantly smaller than the actual average size. I'm not sure how
big of a problem this accuracy is or how it compares to sort, for
instance (it's a bit hard to compare because sort works with
theoretical memory usage while hashagg looks at actual allocated
memory).
Costing was the last major TODO, so I'm considering this feature
complete, though it still needs some work on quality.
Regards,
Jeff Davis
| Attachment | Content-Type | Size |
|---|---|---|
| hashagg-20191227.patch | text/x-patch | 100.3 KB |
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