The IsCTIDVar() tests in nodeTidscan.c and nodeTidrangescan.c
look buggy at first sight: they aren't checking that the varno
matches the table to be scanned. Actually they're safe because
any Var in a scan-level qual must be for the correct table ...
but if we're depending on that, it's pretty pointless to verify
varlevelsup. (Besides which, varlevelsup is *always* zero at
execution, since we've flattened the rangetable long since.)
Remove the useless varlevelsup check, and instead add some
commentary explaining why we don't need to check varno.
Noted while fooling with a planner change that causes the order
of "t1.ctid = t2.ctid" to change in some tidscan.sql tests;
I was briefly fooled into thinking there was a live bug here.
This adds a new executor node named TID Range Scan. The query planner
will generate paths for TID Range scans when quals are discovered on base
relations which search for ranges on the table's ctid column. These
ranges may be open at either end. For example, WHERE ctid >= '(10,0)';
will return all tuples on page 10 and over.
To support this, two new optional callback functions have been added to
table AM. scan_set_tidrange is used to set the scan range to just the
given range of TIDs. scan_getnextslot_tidrange fetches the next tuple
in the given range.
For AMs were scanning ranges of TIDs would not make sense, these functions
can be set to NULL in the TableAmRoutine. The query planner won't
generate TID Range Scan Paths in that case.
Author: Edmund Horner, David Rowley
Reviewed-by: David Rowley, Tomas Vondra, Tom Lane, Andres Freund, Zhihong Yu
Discussion: https://postgr.es/m/CAMyN-kB-nFTkF=VA_JPwFNo08S0d-Yk0F741S2B7LDmYAi8eyA@mail.gmail.com
