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Improved the check that determines if the pattern trick should be used. #118

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Sep 1, 2018
Merged

Improved the check that determines if the pattern trick should be used. #118

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a302e0d
Improved the check that determines if the pattern trick should be used.
floriankramer Aug 30, 2018
b2c41fa
Implemented the changes requested in the review.
floriankramer Aug 31, 2018
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131 changes: 97 additions & 34 deletions src/engine/QueryPlanner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -47,38 +47,11 @@ QueryExecutionTree QueryPlanner::createExecutionTree(ParsedQuery& pq) const {
LOG(DEBUG) << "Got " << patternPlans.size() << " subplans to create."
<< std::endl;

// look for ql:has-predicate to determine if the pattern trick should be used
bool usePatternTrick = false;
// Look for ql:has-predicate to determine if the pattern trick should be used.
// If the pattern trick is used the has predicate triple will be removed from
// the list of where clause triples.
SparqlTriple patternTrickTriple("", "", "");
// Check if the query has the right number of variables for aliases, select
// and group by.
if (pq._groupByVariables.size() == 1 && pq._aliases.size() == 1 &&
pq._selectedVariables.size() == 2) {
const ParsedQuery::Alias& alias = pq._aliases.back();
// Check if the alias is a non distinct count alias
if (alias._isAggregate &&
alias._function.find("DISTINCT") == std::string::npos &&
alias._function.find("distinct") == std::string::npos &&
(ad_utility::startsWith(alias._function, "COUNT") ||
ad_utility::startsWith(alias._function, "count"))) {
// look for a HAS_RELATION_PREDICATE triple
for (size_t i = 0; i < pq._rootGraphPattern._whereClauseTriples.size();
i++) {
const SparqlTriple& t = pq._rootGraphPattern._whereClauseTriples[i];
if (t._p == HAS_PREDICATE_PREDICATE && alias._inVarName == t._o &&
pq._groupByVariables[0] == t._o &&
pq._selectedVariables[0] == t._o &&
pq._selectedVariables[1] == alias._outVarName) {
LOG(DEBUG) << "Using the pattern trick to answer the query." << endl;
usePatternTrick = true;
patternTrickTriple = t;
// remove the triple from the graph
pq._rootGraphPattern._whereClauseTriples.erase(
pq._rootGraphPattern._whereClauseTriples.begin() + i);
}
}
}
}
bool usePatternTrick = checkUsePatternTrick(pq, patternTrickTriple);

bool doGrouping = pq._groupByVariables.size() > 0 || usePatternTrick;
if (!doGrouping) {
Expand Down Expand Up @@ -275,7 +248,7 @@ QueryExecutionTree QueryPlanner::createExecutionTree(ParsedQuery& pq) const {
std::shared_ptr<Operation> orderByOp(
new OrderBy(_qec, final._qet, sortIndices));

if (isSorted) {
if (!isSorted) {
orderByPlan._qet->setVariableColumns(
final._qet->getVariableColumnMap());
orderByPlan._qet->setOperation(QueryExecutionTree::ORDER_BY, orderByOp);
Expand All @@ -294,8 +267,8 @@ QueryExecutionTree QueryPlanner::createExecutionTree(ParsedQuery& pq) const {
countPred);

final = patternTrickPlan;
std::cout << "Plan after pattern trick: " << endl
<< final._qet->asString() << endl;
LOG(DEBUG) << "Plan after pattern trick: " << endl
<< final._qet->asString() << endl;
} else {
// Use the pattern trick without a subtree
SubtreePlan patternTrickPlan(_qec);
Expand Down Expand Up @@ -434,6 +407,96 @@ QueryExecutionTree QueryPlanner::createExecutionTree(ParsedQuery& pq) const {
return *final._qet.get();
}

bool QueryPlanner::checkUsePatternTrick(
ParsedQuery& pq, SparqlTriple& patternTrickTriple) const {
bool usePatternTrick = false;
// Check if the query has the right number of variables for aliases and group
// by.
if (pq._groupByVariables.size() == 1 && pq._aliases.size() == 1) {
const ParsedQuery::Alias& alias = pq._aliases.back();
// Check if the alias is a non distinct count alias
if (alias._isAggregate &&
alias._function.find("DISTINCT") == std::string::npos &&
alias._function.find("distinct") == std::string::npos &&
(ad_utility::startsWith(alias._function, "COUNT") ||
ad_utility::startsWith(alias._function, "count"))) {
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can we do these checks on the lowercase aliass._function so it's actually case insensitive?

// look for a HAS_RELATION_PREDICATE triple
for (size_t i = 0; i < pq._rootGraphPattern._whereClauseTriples.size();
i++) {
const SparqlTriple& t = pq._rootGraphPattern._whereClauseTriples[i];
// Check that the triples predicates is the HAS_PREDICATE_PREDICATE.
// Also check that the triples object matches the aliases input variable
// and the group by variable.
if (t._p == HAS_PREDICATE_PREDICATE && alias._inVarName == t._o &&
pq._groupByVariables[0] == t._o) {
// Assume we will use the pattern trick for now but run several more
// checks before actually modifying the query.
usePatternTrick = true;
// check that all selected variables are outputs of
// CountAvailablePredicates
for (const std::string& s : pq._selectedVariables) {
if (s != t._o && s != alias._outVarName) {
usePatternTrick = false;
break;
}
}
// Check for triples containing the has predicates triples object.
for (size_t j = 0;
j < pq._rootGraphPattern._whereClauseTriples.size() &&
usePatternTrick;
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swap the two sides of the && so one immediately sees that this only applies if usePatternTrick == true

j++) {
const SparqlTriple& other =
pq._rootGraphPattern._whereClauseTriples[j];
if (j != i &&
(other._s == t._o || other._p == t._o || other._o == t._o)) {
usePatternTrick = false;
}
}
// Check for filters on the has predicate triples subject or object
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write "ql:has-predicate triple's" without the "-" the English sounds a bit weird

for (const SparqlFilter& filter : pq._rootGraphPattern._filters) {
if (filter._lhs == t._o || filter._lhs == t._s ||
filter._rhs == t._o || filter._rhs == t._s) {
usePatternTrick = false;
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Ok, but in this case we still have a a ql:has-predicate in the query, am I assuming correctly that without the userPatternTrick flag bein set this will be computed in the classic SPARQL way and will still work or does the query fail?

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If the usePatternTrick flag is not set the query should still work the normal way.

break;
}
}
// Check for optional parts containing the has predicate triples
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add a "-" here too

// object
std::vector<const ParsedQuery::GraphPattern*> graphsToProcess;
graphsToProcess.insert(graphsToProcess.end(),
pq._rootGraphPattern._children.begin(),
pq._rootGraphPattern._children.end());
while (!graphsToProcess.empty()) {
const ParsedQuery::GraphPattern* pattern = graphsToProcess.back();
graphsToProcess.pop_back();
graphsToProcess.insert(graphsToProcess.end(),
pattern->_children.begin(),
pattern->_children.end());
for (const SparqlTriple& other : pattern->_whereClauseTriples) {
if (other._s == t._o || other._p == t._o || other._o == t._o) {
usePatternTrick = false;
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Same question as above

break;
}
}
if (!usePatternTrick) {
break;
}
}
if (usePatternTrick) {
LOG(DEBUG) << "Using the pattern trick to answer the query."
<< endl;
patternTrickTriple = t;
// remove the triple from the graph
pq._rootGraphPattern._whereClauseTriples.erase(
pq._rootGraphPattern._whereClauseTriples.begin() + i);
}
}
}
}
}
return usePatternTrick;
}

// _____________________________________________________________________________
vector<QueryPlanner::SubtreePlan> QueryPlanner::getOrderByRow(
const ParsedQuery& pq, const vector<vector<SubtreePlan>>& dpTab) const {
Expand Down
2 changes: 2 additions & 0 deletions src/engine/QueryPlanner.h
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Original file line number Diff line number Diff line change
Expand Up @@ -201,4 +201,6 @@ class QueryPlanner {
SubtreePlan getTextLeafPlan(const TripleGraph::Node& node) const;

SubtreePlan optionalJoin(const SubtreePlan& a, const SubtreePlan& b) const;
bool checkUsePatternTrick(ParsedQuery& pq,
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Please add a method comment here. Also Google's C++ style guide, which we try to follow, forbids non-const reference parameters and they aren't really used in the rest of the code base. So these need to be pointers instead.

SparqlTriple& patternTrickTriple) const;
};