| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Donald Dong <xdong(at)csumb(dot)edu> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, David Fetter <david(at)fetter(dot)org>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: Actual Cost |
| Date: | 2019-02-17 05:31:33 |
| Message-ID: | 9871.1550381493@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Donald Dong <xdong(at)csumb(dot)edu> writes:
> On Feb 16, 2019, at 6:44 PM, Tomas Vondra wrote:
>> I don't quite understand what is meant by "actual cost metric" and/or
>> how is that different from running EXPLAIN ANALYZE.
> Here is an example:
> Hash Join (cost=3.92..18545.70 rows=34 width=32) (actual cost=3.92..18500 time=209.820..1168.831 rows=47 loops=3)
> Now we have the actual time. Time can have a high variance (a change
> in system load, or just noises), but I think the actual cost would be
> less likely to change due to external factors.
I'm with Tomas: you have not explained what you think those
numbers mean.
regards, tom lane
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