Message-ID: <886b209f-8736-9cf2-ab9c-89870dea7bd8@enterprisedb.com>
Date: Thu, 2 Nov 2023 22:25:16 +0100
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Subject: Re: Detoasting optionally to make Explain-Analyze less misleading
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To: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: stepan rutz <stepan.rutz@gmx.de>, Tom Lane <tgl@sss.pgh.pa.us>,
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
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On 11/2/23 21:02, Matthias van de Meent wrote:
> On Thu, 2 Nov 2023 at 20:32, Tomas Vondra <tomas.vondra@enterprisedb.com> wrote:
>> On 11/2/23 20:09, stepan rutz wrote:
>>> db1=# explain (analyze, serialize) select * from test;
>>>                                             QUERY PLAN
>>> ---------------------------------------------------------------------------------------------------
>>>  Seq Scan on test  (cost=0.00..22.00 rows=1200 width=40) (actual
>>> time=0.023..0.027 rows=1 loops=1)
>>>  Planning Time: 0.077 ms
>>>  Execution Time: 303.281 ms
>>>  Serialized Bytes: 78888953 Bytes. Mode Text. Bandwidth 248.068 MB/sec
>> [...]
>> BTW if you really want to print amount of memory, maybe print it in
>> kilobytes, like every other place in explain.c?
> 
> Isn't node width in bytes, or is it an opaque value not to be
> interpreted by users? I've never really investigated that part of
> Postgres' explain output...
> 

Right, "width=" is always in bytes. But fields like amount of sorted
data is in kB, and this seems closer to that.

>> Also, explain generally
>> prints stuff in "key: value" style (in text format).
> 
> That'd be key: metrickey=metricvalue for expanded values like those in
> plan nodes and the buffer usage, no?
> 

Possibly. But the proposed output does neither. Also, it starts with
"Serialized Bytes" but then prints info about bandwidth.


>>>  Serialized Bytes: 78888953 Bytes. Mode Text. Bandwidth 248.068 MB/sec
> 
> I was thinking more along the lines of something like this:
> 
> [...]
> Execution Time: xxx ms
> Serialization: time=yyy.yyy (in ms) size=yyy (in KiB, or B) mode=text
> (or binary)
> > This is significantly different from your output, as it doesn't hide
> the measured time behind a lossy calculation of bandwidth, but gives
> the measured data to the user; allowing them to derive their own
> precise bandwidth if they're so inclined.
> 

Might work. I'm still not convinced we need to include the mode, or that
the size is that interesting/useful, though.


regards

-- 
Tomas Vondra
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