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Stop bfs early when possible

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Summary: When doing bfs with given endpoint, we can stop the traversal on first successful pull.

Reviewers: teon.banek, msantl, mculinovic, buda

Reviewed By: msantl

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1469
This commit is contained in:
Marin Tomic 2018-07-06 15:26:59 +02:00 committed by Teon Banek
parent 1c2f599a93
commit e2f9eb6fa5
1 changed files with 81 additions and 62 deletions
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23
src/query/plan/operator.cpp
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@ -1079,8 +1079,10 @@ class ExpandBfsCursor : public query::plan::Cursor {
// if current is still empty, it means both are empty, so pull from
// input
if (to_visit_current_.empty()) {
if (skip_rest_ || to_visit_current_.empty()) {
if (!input_cursor_->Pull(frame, context)) return false;
to_visit_current_.clear();
to_visit_next_.clear();
processed_.clear();
auto vertex_value = frame[self_.input_symbol_];
@ -1098,6 +1100,7 @@ class ExpandBfsCursor : public query::plan::Cursor {
? EvaluateInt(evaluator, self_.upper_bound_,
"Max depth in breadth-first expansion")
: std::numeric_limits<int>::max();
skip_rest_ = false;
if (upper_bound_ < 1)
throw QueryRuntimeException(
"Max depth in breadth-first expansion must be greater then "
@ -1137,6 +1140,9 @@ class ExpandBfsCursor : public query::plan::Cursor {
TypedValue &node = frame[self_.node_symbol_];
// due to optional matching the existing node could be null
if (node.IsNull() || (node != expansion.second).Value<bool>()) continue;
// there is no point in traversing the rest of the graph because bfs
// can find only one path to a certain node
skip_rest_ = true;
} else
frame[self_.node_symbol_] = expansion.second;
@ -1163,6 +1169,9 @@ class ExpandBfsCursor : public query::plan::Cursor {
int lower_bound_{-1};
int upper_bound_{-1};
// when set to true, expansion is restarted from a new source
bool skip_rest_{false};
// maps vertices to the edge they got expanded from. it is an optional
// edge because the root does not get expanded from anything.
// contains visited vertices as well as those scheduled to be visited.
@ -1203,6 +1212,7 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
while (true) {
TypedValue last_vertex;
if (!skip_rest_) {
if (current_depth_ >= lower_bound_) {
for (; pull_pos_ != subcursor_ids_.end(); ++pull_pos_) {
auto vertex = db_.db().bfs_subcursor_clients().Pull(
@ -1222,6 +1232,9 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
TypedValue &node = frame[self_.node_symbol_];
// Due to optional matching the existing node could be null
if (node.IsNull() || (node != last_vertex).ValueBool()) continue;
// There is no point in traversing the rest of the graph because BFS
// can find only one path to a certain node.
skip_rest_ = true;
} else {
frame[self_.node_symbol_] = last_vertex;
}
@ -1243,7 +1256,8 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
while (true) {
DCHECK(static_cast<bool>(current_edge_addr) ^
static_cast<bool>(current_vertex_addr))
<< "Exactly one of `current_edge_addr` or `current_vertex_addr` "
<< "Exactly one of `current_edge_addr` or "
"`current_vertex_addr` "
"should be set during path reconstruction";
auto ret = current_edge_addr
? db_.db().bfs_subcursor_clients().ReconstructPath(
@ -1275,6 +1289,7 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
continue;
}
}
}
VLOG(10) << "Trying to get a new source...";
// We're done with this source, try getting a new one
@ -1294,6 +1309,7 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
? EvaluateInt(evaluator, self_.upper_bound_,
"Max depth in breadth-first expansion")
: std::numeric_limits<int>::max();
skip_rest_ = false;
if (upper_bound_ < 1) {
throw QueryRuntimeException(
@ -1323,6 +1339,9 @@ class DistributedExpandBfsCursor : public query::plan::Cursor {
int lower_bound_{-1};
int upper_bound_{-1};
// When set to true, expansion is restarted from a new source.
bool skip_rest_{false};
// Current depth. Reset for each new expansion, the initial value is
// irrelevant.
int current_depth_{-1};