Re: explain HashAggregate to report bucket and memory stats

On Fri, Mar 06, 2020 at 09:58:59AM -0800, Andres Freund wrote:
> ...
>
>> + }
>> + else if (!inst->nbuckets)
>> + ; /* Do nothing */
>> + else
>> + {
>> + if (inst->nbuckets_original != inst->nbuckets)
>> + {
>> + ExplainIndentText(es);
>> + appendStringInfo(es->str,
>> + "Buckets: %ld (originally %ld)",
>> + inst->nbuckets,
>> + inst->nbuckets_original);
>> + }
>> + else
>> + {
>> + ExplainIndentText(es);
>> + appendStringInfo(es->str,
>> + "Buckets: %ld",
>> + inst->nbuckets);
>> + }
>> +
>> + if (es->analyze)
>> + appendStringInfo(es->str,
>> + " Memory Usage: hashtable: %ldkB, tuples: %ldkB",
>> + spacePeakKb_hash, spacePeakKb_tuples);
>> + appendStringInfoChar(es->str, '\n');
>
>I'm not sure I like the alternative output formats here. All the other
>fields are separated with a comma, but the original size is in
>parens. I'd probably just format it as "Buckets: %lld " and then add
>", Original Buckets: %lld" when differing.
>

FWIW this copies hashjoin precedent, which does this:

appendStringInfo(es->str,
"Buckets: %d (originally %d) Batches: %d (originally %d) Memory Usage: %ldkB\n",
hinstrument.nbuckets,
...

I agree it's not ideal, but maybe let's not invent new ways to format
the same type of info.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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