| From: | Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> |
|---|---|
| To: | "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Peter Geoghegan <pg(at)bowt(dot)ie>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: 64-bit queryId? |
| Date: | 2017-10-02 20:42:42 |
| Message-ID: | c8144ca1-ba28-fba7-d05c-fe509c3dcf27@archidevsys.co.nz |
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| Lists: | pgsql-hackers |
On 03/10/17 04:02, Joshua D. Drake wrote:
> On 10/01/2017 04:22 PM, Robert Haas wrote:
>> On Sun, Oct 1, 2017 at 3:48 PM, Greg Stark <stark(at)mit(dot)edu> wrote:
>>> Well these kinds of monitoring systems tend to be used by operations
>>> people who are a lot more practical and a lot less worried about
>>> theoretical concerns like that.
>>
>> +1, well said.
>>
>>> In context the point was merely that the default
>>> pg_stat_statements.max of 5000 isn't sufficient to argue that 32-bit
>>> values are enough. It wouldn't be hard for there to be 64k different
>>> queries over time and across all the databases in a fleet and at that
>>> point it becomes likely there'll be a 32-bit collision.
>>
>> Yeah.
>>
>> I think Alexander Korotkov's points are quite good, too.
>>
>
> +1 to both of these as well.
>
> jD
>
Did a calculation:
# probability of collision
54561 0.499993
54562 0.500005
Essentially, you hit a greater than 50% chance of a collision before you
get to 55 thousand statements.
Cheers,
Gavin
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