Re: BUG #15144: *** glibc detected *** postgres: postgres smsconsole[local] SELECT: double free or corruption (!pre

On 2018-04-16 14:03:40 -0300, Alvaro Herrera wrote:
> Peter Geoghegan wrote:
> 
> > This now seems unnecessary, since it's already evident from your "bt
> > full" output that the query involved in the crash was "select count(*)
> > from pg_buffercache where isdirty".
> 
> Hmm, so is the Zabbix monitoring running that query frequently?
> Because, as I recall, pg_buffercache is pretty heavy on the system,
> since it needs to acquire all the bufmgr locks simultaneously?
> 
> In other words, this seems a terrible query to be running in zabbix.

Can be extremely useful however, to predict how much longer your
workload's hot data set fits into cache. That's worth the cost in a
number of cases...  Either way, a crash is clearly something separate.


> I have vague memories of somebody submitting a version of this code
> that returned approximate answers, good enough for monitoring ...

That might have been me, but I don't recall the details anymore...

Greetings,

Andres Freund