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Centralize fixups for mismatched nullingrels in nestloop params.

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It turns out that the fixes we applied in commits bfd332b3f
and 63e4f13d2 were not nearly enough to solve the problem.
We'd focused narrowly on subquery RTEs with lateral references,
but lateral references can occur in several other RTE kinds
such as function RTEs.  Putting the same hack into half a dozen
code paths seems quite unattractive.  Hence, revert the code changes
(but not the test cases) from those commits and instead solve it
centrally in identify_current_nestloop_params(), as Richard proposed
originally.  This is a bit annoying because it could mask erroneous
nullingrels in nestloop params that are generated from non-LATERAL
parameterized paths; but on balance I don't see a better way.
Maybe at some future time we'll be motivated to find a more rigorous
approach to nestloop params, but that's not happening for beta2.

Richard Guo and Tom Lane

Discussion: https://postgr.es/m/CAMbWs48Jcw-NvnxT23WiHP324wG44DvzcH1j4hc0Zn+3sR9cfg@mail.gmail.com
This commit is contained in:
Tom Lane
2023-06-20 10:22:52 -04:00
parent 5961141646
commit 0655c03ef9
5 changed files with 69 additions and 72 deletions
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37
src/backend/optimizer/path/joinpath.c
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@@ -430,24 +430,6 @@ have_unsafe_outer_join_ref(PlannerInfo *root,
* These are returned in parallel lists in *param_exprs and *operators.
* We also set *binary_mode to indicate whether strict binary matching is
* required.
*
* A complication is that innerrel's lateral_vars may contain nullingrel
* markers that need adjustment. This occurs if we have applied outer join
* identity 3,
* (A leftjoin B on (Pab)) leftjoin C on (Pb*c)
* = A leftjoin (B leftjoin C on (Pbc)) on (Pab)
* and C contains lateral references to B. It's still safe to apply the
* identity, but the parser will have created those references in the form
* "b*" (i.e., with varnullingrels listing the A/B join), while what we will
* have available from the nestloop's outer side is just "b". We deal with
* that here by stripping the nullingrels down to what is available from the
* outer side according to outerrel->relids.
* That fixes matters for the case of forward application of identity 3.
* If the identity was applied in the reverse direction, we will have
* innerrel's lateral_vars containing too few nullingrel bits rather than
* too many. Currently, that causes no problems because setrefs.c applies
* only a subset check to nullingrels in NestLoopParams, but we'd have to
* work harder if we ever want to tighten that check.
*/
static bool
paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
@@ -551,25 +533,6 @@ paraminfo_get_equal_hashops(PlannerInfo *root, ParamPathInfo *param_info,
return false;
}
/* OK, but adjust its nullingrels before adding it to result */
expr = copyObject(expr);
if (IsA(expr, Var))
{
Var *var = (Var *) expr;
var->varnullingrels = bms_intersect(var->varnullingrels,
outerrel->relids);
}
else if (IsA(expr, PlaceHolderVar))
{
PlaceHolderVar *phv = (PlaceHolderVar *) expr;
phv->phnullingrels = bms_intersect(phv->phnullingrels,
outerrel->relids);
}
else
Assert(false);
*operators = lappend_oid(*operators, typentry->eq_opr);
*param_exprs = lappend(*param_exprs, expr);