Re: Intermittent regression test failure from index-only scans patch

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Oct 8, 2011, at 11:04 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I'm inclined to fix this by changing the test to examine idx_tup_read
>> not idx_tup_fetch. Alternatively, we could have the test force
>> enable_indexonlyscan off. Thoughts?

> No preference.

I ended up doing it the second way (ie enable_indexonlyscan = off)
because it turns out that pg_stat_user_tables doesn't have the
idx_tup_read column --- we track that count per index, not per table.
I could have complicated the test's stats queries some more, but it
seemed quite not relevant to the goals of the test.

> Should we have another counter for heap fetches avoided? Seems like that could be useful to know.

Hm. I'm hesitant to add another per-table (or per index?) statistics
counter because of the resultant bloat in the stats file. But it
wouldn't be a bad idea for somebody to take two steps back and rethink
what we're counting in this area. The current counter definitions are
mostly backwards-compatible with pre-8.1 behavior, and it seems like the
goalposts have moved enough that maybe it's time to break compatibility.

regards, tom lane