// is this entire expression cacheable after this phase?
NABoolean Join::isCacheableExpr(CacheWA& cwa)
{
if (cwa.getPhase() >= CmpMain::BIND) {
// must first descend to scans to get cwa.numberOfScans_
if (!RelExpr::isCacheableExpr(cwa)) {
return FALSE;
}
if (isCacheableNode(cwa.getPhase())) {
cwa.setConditionallyCacheable();
}
// if we allow joins of views to be cached, query caching cannot
// distinguish between (see note at bottom of cachewa.h)
// select avg(f.a) from v f, v s group by f.b;
// select avg(s.a) from v f, v s group by f.b;
// select avg(t.a) from v f, t group by f.b;
// assuming v is "create view v from select * from t". We avoid
// false cache hits by detecting the possible occurrence of such
// view joins here and later using cwa.isViewJoin_ to include
// their query texts into their cache keys.
//
// A view is repsented by a renamed table with isView() returnning
// TRUE.
RelExpr *c0 = child(0);
RelExpr *c1 = child(1);
if ((c0->getOperatorType() == REL_RENAME_TABLE &&
((RenameTable *)c0)->isView() == TRUE)
||
(c1->getOperatorType() == REL_RENAME_TABLE &&
((RenameTable *)c1)->isView() == TRUE)) {
cwa.foundViewJoin();
}
// check its join predicate
ItemExpr *pred = joinPredTree_ ? joinPredTree_ :
joinPred_.rebuildExprTree();
if (pred) {
cwa.setHasPredicate();
// is join predicate cacheable?
if (pred->hasNoLiterals(cwa)) {
// predicate with no literals is cacheable
}
else {
cwa.setPredHasNoLit(FALSE);
if (!pred->isCacheableExpr(cwa)) {
// a non-cacheable predicate renders Join non-cacheable.
setNonCacheable();
return FALSE;
}
}
}
return TRUE; // join may be cacheable
}
return FALSE;
}
