Performance Optimization for Indicator Relations

[b-scholz]

Example:

R(x) :- A(_), B(x). 

Transfer tuples from relation B to relation R if relation is not empty. Semantically, this can be interpreted as

R(x) :- size(A)>0, B(x). 

Souffle currently does not provide this optimization.

[mmcgr]

Did this get worked on?
Currently the compiled version turns R(x) :- A(_), B(x). into

if (!rel_1_A->empty()) {
  for (const auto& env1 : *rel_2_B) {

Which seems to be what you describe.
I think the relevant parts of the code are

souffle/src/RamTranslator.cpp

Lines 668 to 673 in 1392c67

	bool isExistCheck = !valueIndex.isSomethingDefinedOn(level);
	for (size_t pos = 0; pos < atom->argSize(); ++pos) {
	if (dynamic_cast<AstAggregator*>(atom->getArgument(pos))) {
	isExistCheck = false;
	}
	}

and

souffle/src/RamExecutor.cpp

Lines 483 to 488 in 1392c67

	if (scan.getRangeQueryColumns() == 0) {
	// if scan is not binding anything => check for emptiness
	if (scan.isPureExistenceCheck() && !rel.empty()) {
	visitSearch(scan);
	return;
	}

[b-scholz]

This has been fixed.