On Tue, Nov 11, 2014 at 2:14 AM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> I'm not sure why you say opaque is not associated with the specific
> scan. Are you thinking we could reuse opaque for a future scan? I
> think we could consider that opaque *is* the place to cache things such
> as the hashed value of the qual constants or whatever.
Oh. I guess this goes back to my original suggestion that the API docs
need to explain some sense of when OpcInfo is called. I didn't realize
it was tied to a specific scan. This does raise the question of why
the scan information isn't available in OpcInfo though. That would let
me build the hash value in a natural place instead of having to do it
lazily which I find significantly more awkward.
Is it possible for scan keys to change between calls for nested loop
joins or quirky SQL with volatile functions in the scan or anything? I
guess that would prevent the index scan from being used at all. But I
can be reassured the Opcinfo call will be called again when a cached
plan is reexecuted? Stable functions might have new values in a
subsequent execution even if the plan hasn't changed at all for
example.
> That's to test the Union procedure; if you look at the code, it's just
> used in assert-enabled builds. Now that I think about it, perhaps this
> can turn out to be problematic for your bloom filter opclass. I
> considered the idea of allowing the opclass to disable this testing
> procedure, but it isn't done (yet.)
No, it isn't a problem for my opclass other than performance, it was
quite helpful in turning up bugs early in fact. It was just a bit
confusing because I was trying to test things one by one and it turned
out the assertion checks meant a simple insert turned up bugs in Union
which I hadn't expected. But it seems perfectly sensible in an
assertion check.
--
greg