Re: Re: Missing rows with index scan when collation is not "C" (PostgreSQL 9.5)

On Thu, Mar 24, 2016 at 7:14 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> However, the fact that the patch is not "Ready for Committer" at this
> point means that it is not going to be available in time for next
> week's maintenance releases, or very possibly, for 9.6.  Time grows
> very short.

The only people that are likely comfortable giving final sign-off on
it that are active this CF are Tom and Kevin. That is an awkward
situation.

I could produce a 9.5 variant that had even more limited scope than
what's in the CF. That would be strictly limited to checking page
order, and the high key invariant. It wouldn't check relationships
spanning multiple pages, either on the same level, or though
parent/child relationships. Then, I think significantly less expertise
is required for review, because locking protocols and so on don't
enter into it.

I think that the risk of getting something wrong with amcheck as
things stand is acceptable for 9.6, and maybe even 9.5. About the
worst case scenario is a false positive report of corruption. But with
the tool scoped at only looking at really obvious invariants at the
level of a single page, which is what I'd propose for 9.5, it seems
like the risk of bugs would be very well managed. That would still
catch issues caused by this glibc bug very reliable.

Keep in mind that in general, amcheck does nothing special with buffer
locks + pins -- it just acquires a pin +shared buffer lock on one
buffer/page at a time, copies it into local memory, and releases and
drops the pin. So, all processing by amcheck happens outside any
critical path.

I could work hard to get that stripped down amcheck into 9.5. I'm
already behind on my CF reviews, and time is short, so it would be
good if we moved quickly on this, either way....

--
Peter Geoghegan