Re: Add a bound check to TidRangeEval

On Wed, 11 Jun 2025 at 14:26, Junwang Zhao <zhjwpku(at)gmail(dot)com> wrote:
> This is not a common case, it's just a corner case while
> playing around the TidRangeScan.
>
> I'm not saying this is an optimization, it just makes me a little
> confused when I see the lowerBound > upperBound and
> it still returns true.
>
> The comments say "Returns true if it's possible for the
> range to contain tuples." This seems not fully accurate?

The word "possible" there is meant to convey that false negatives are
*not* ok, but false positives are fine. I'm certainly open to making
the comment better if that's not clear.

How about adding "We don't bother validating that trss_mintid is less
than or equal to trss_maxtid, as the scan_set_tidrange() table AM
function will detect that."

The scan_set_tidrange function does document that it's the
implementation's responsibility to check this, as the comment in the
declaration of struct TableAmRoutine reads:

* Implementations of scan_set_tidrange must themselves handle
* ItemPointers of any value. i.e, they must handle each of the following:
*
* 1) mintid or maxtid is beyond the end of the table; and
* 2) mintid is above maxtid; and
* 3) item offset for mintid or maxtid is beyond the maximum offset
* allowed by the AM.

So I'm not keen to add code to TidRangeEval to check for this as it
would result in additional overhead for valid usages of TID Range
scans.

David