@Override
protected AbstractPlanNode recursivelyApply(AbstractPlanNode plan) {
assert (plan != null);
// depth first:
// find AggregatePlanNode with exactly one child
// where that child is an AbstractScanPlanNode.
// Replace any qualifying AggregatePlanNode / AbstractScanPlanNode pair
// with an IndexCountPlanNode or TableCountPlanNode
ArrayList<AbstractPlanNode> children = new ArrayList<AbstractPlanNode>();
for (int i = 0; i < plan.getChildCount(); i++) children.add(plan.getChild(i));
for (AbstractPlanNode child : children) {
// TODO this will break when children feed multiple parents
AbstractPlanNode newChild = recursivelyApply(child);
// Do a graft into the (parent) plan only if a replacement for a child was found.
if (newChild == child) {
continue;
}
boolean replaced = plan.replaceChild(child, newChild);
assert (true == replaced);
}
// check for an aggregation of the right form
if ((plan instanceof AggregatePlanNode) == false) return plan;
assert (plan.getChildCount() == 1);
AggregatePlanNode aggplan = (AggregatePlanNode) plan;
// ENG-6131 fixed here.
if (!(aggplan.isTableCountStar()
|| aggplan.isTableNonDistinctCountConstant()
|| aggplan.isTableCountNonDistinctNullableColumn())) {
return plan;
}
AbstractPlanNode child = plan.getChild(0);
// A table count can replace a seq scan only if it has no predicates.
if (child instanceof SeqScanPlanNode) {
if (((SeqScanPlanNode) child).getPredicate() != null) {
return plan;
}
AbstractExpression postPredicate = aggplan.getPostPredicate();
if (postPredicate != null) {
List<AbstractExpression> aggList =
postPredicate.findAllSubexpressionsOfClass(AggregateExpression.class);
boolean allCountStar = true;
for (AbstractExpression expr : aggList) {
if (expr.getExpressionType() != ExpressionType.AGGREGATE_COUNT_STAR) {
allCountStar = false;
break;
}
}
if (allCountStar) {
return plan;
}
}
if (hasInlineLimit(aggplan)) {
// table count EE executor does not handle inline limit stuff
return plan;
}
return new TableCountPlanNode((AbstractScanPlanNode) child, aggplan);
}
// Otherwise, optimized counts only replace particular cases of index scan.
if ((child instanceof IndexScanPlanNode) == false) return plan;
IndexScanPlanNode isp = (IndexScanPlanNode) child;
// Guard against (possible future?) cases of indexable subquery.
if (((IndexScanPlanNode) child).isSubQuery()) {
return plan;
}
// An index count or table count can replace an index scan only if it has no (post-)predicates
// except those (post-)predicates are artifact predicates we added for reverse scan purpose only
if (isp.getPredicate() != null && !isp.isPredicatesOptimizableForAggregate()) {
return plan;
}
// With no start or end keys, there's not much a counting index can do.
if (isp.getEndExpression() == null && isp.getSearchKeyExpressions().size() == 0) {
// An indexed query without a where clause can fall back to a plain old table count.
// This can only happen when a confused query like
// "select count(*) from table order by index_key;"
// meets a naive planner that doesn't just cull the no-op ORDER BY. Who, us?
if (hasInlineLimit(aggplan)) {
return plan;
}
return new TableCountPlanNode(isp, aggplan);
}
// check for the index's support for counting
Index idx = isp.getCatalogIndex();
if (!idx.getCountable()) {
return plan;
}
// The core idea is that counting index needs to know the start key and end key to
// jump to to get counts instead of actually doing any scanning.
// Options to be determined are:
// - whether each of the start/end keys is missing, partial (a prefix of a compund key), or
// complete,
// - whether the count should include or exclude entries exactly matching each of the start/end
// keys.
// Not all combinations of these options are supported;
// unsupportable cases cause the factory method to return null.
IndexCountPlanNode countingPlan = IndexCountPlanNode.createOrNull(isp, aggplan);
if (countingPlan == null) {
return plan;
}
return countingPlan;
}