Re: [PATCH] pg_stat_toast

Am 12.12.21 um 22:52 schrieb Andres Freund:
> Hi,
> 
> On 2021-12-12 17:20:58 +0100, Gunnar "Nick" Bluth wrote:
>> Please have a look at the attached patch, which implements some statistics
>> for TOAST.
>>
>> The idea (and patch) have been lurking here for quite a while now, so I
>> decided to dust it off, rebase it to HEAD and send it out for review today.
>>
>> A big shoutout to Georgios Kokolatos, who gave me a crash course in PG
>> hacking, some very useful hints and valueable feedback early this year.
>>
>> I'd like to get some feedback about the general idea, approach, naming etc.
>> before refining this further.
> 
> I'm worried about the additional overhead this might impose. For some workload
> it'll substantially increase the amount of stats traffic. Have you tried to
> qualify the overheads? Both in stats size and in stats management overhead?

I'd lie if I claimed so...

Regarding stats size; it adds one PgStat_BackendToastEntry 
(PgStat_BackendAttrIdentifier + PgStat_ToastCounts, should be 56-64 
bytes or something in that ballpark) per TOASTable attribute, I can't 
see that make any system break sweat ;-)

A quick run comparing 1.000.000 INSERTs (2 TOASTable columns each) with 
and without "pgstat_track_toast" resulted in 12792.882 ms vs. 12810.557 
ms. So at least the call overhead seems to be neglectible.

Obviously, this was really a quick run and doesn't reflect real life.
I'll have the machine run some reasonable tests asap, also looking at 
stat size, of course!

Best regards,
-- 
Gunnar "Nick" Bluth

Eimermacherweg 106
D-48159 Münster

Mobil +49 172 8853339
Email: gunnar.bluth@pro-open.de
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