Re: Access statistics

Tom Lane wrote:
> Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> > Here it comes.
>
> Hm. I really don't like the way you've uglified the heap_fetch
> interface; can't that be done better? It's just plain bizarre that
> heap_fetch is now responsible for counting stats for index scans.
> And surely this bit of code is wrong:
>
> *userbuf = buffer;
> +
> + if (iscan != NULL)
> + pgstat_count_heap_fetch(&iscan->xs_pgstat_info);
> + else
> + pgstat_count_heap_fetch(&relation->pgstat_info);
> }
>
> You can't count heapscan info via the relcache entry --- what if there's
> more than one heapscan in progress on the same rel? What if the
> relcache entry gets rebuilt by SI invalidation? I don't think the stats
> stuff should touch the relcache at all.

The counting end's up in one and the same global slot of the
tabstat messages. These slots are collected per frontend
command and are identified by the tables oid. Does it matter
how often the pointer to that slot is updated to the same
value?

>
> There's been talk in the past of trying to unify the heapscan and
> indexscan APIs, so that we wouldn't need ugliness like the two sets of
> coding in AttrDefaultFetch and similar places. Maybe it's time to bite
> that bullet, if it'd provide a cleaner place to put the stats calls.

Exactly that's the problem. Only heap_fetch() knows if the
tid passed in is visible or not, so right now the counting
could be done there or in all the places where heap_fetch()
is called.

>
> Also, I do not like the pgStatPmPipe mechanism for detecting postmaster
> shutdown. That eats two file descriptors in every backend, which is a
> pretty substantial waste of resources. Why not just have the postmaster
> send a signal to the stats collector when it's time to shut down?

Don't kill -9 the postmaster :-)

Well, we could do the signal *plus* having the child checking
from time to time with a zero kill if the postmaster died to
suizide in case.

>
> BTW, PG_FUNCTION_INFO_V1() is not needed for built-in functions.

Survived somehow from the time where they resided in a
loadable module.

Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck(at)Yahoo(dot)com #

_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com