Re: Optimize mergejoinscansel() by avoiding redundant computations

Hi

Build on v2 by adding checks in the recursive calls to find_relation_rte() to ensure that
the relevant Var properties match, as shown below:
/*
* We can only recurse through a simple Var of the subquery's query
* level, and only if its varattno, vartype, vartypmod, varcollid, and
* varreturningtype properties match those of the upper Var.
*/
if (tmpvar && IsA((tmpvar), Var) &&
tmpvar->varlevelsup == 0)
{
if (tmpvar->varattno <= 0 ||
tmpvar->vartype != (*var)->vartype ||
tmpvar->vartypmod != (*var)->vartypmod ||
tmpvar->varcollid != (*var)->varcollid ||
tmpvar->varreturningtype != (*var)->varreturningtype)
goto fail;

/* OK, recurse into the subquery. */
*var = tmpvar;
return find_relation_rte(subroot, var);
}

Also, revise the comments in find_relation_rte() and simplify its implementation, using examine_simple_variable() as a reference.

regards,
--
ZizhuanLiu (X-MAN) 
44973863(at)qq(dot)com