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Add limiting number of generated plans for a query

Browse Source 
Reviewers: florijan, mislav.bradac

Reviewed By: mislav.bradac

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D548
This commit is contained in:
Teon Banek 2017-07-13 12:57:55 +02:00
parent d66d9e3b40
commit 99e27cb7e9
1 changed files with 44 additions and 0 deletions
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44
src/query/plan/variable_start_planner.cpp
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@ -1,5 +1,16 @@
#include "query/plan/planner.hpp"
#include <limits>
#include <gflags/gflags.h>
#include <glog/logging.h>
#include "utils/flag_validation.hpp"
DEFINE_VALIDATED_uint64(
query_max_plans, 1000U, "Maximum number of generated plans for a query",
FLAG_IN_RANGE(1, std::numeric_limits<std::uint64_t>::max()));
namespace query::plan {
namespace {
@ -153,6 +164,37 @@ std::vector<std::vector<T>> CartesianProduct(
return products;
}
template <typename T>
std::uint64_t CartesianProductSize(const std::vector<std::vector<T>> &sets) {
std::uint64_t n = 1U;
for (const auto &set : sets) {
if (set.empty()) {
return 0U;
}
std::uint64_t new_n = n * set.size();
if (new_n < n || new_n < set.size()) {
DLOG(WARNING) << "Unsigned wrap-around when calculating expected size of "
"Cartesian product.";
return std::numeric_limits<std::uint64_t>::max();
}
n = new_n;
}
return n;
}
// Shortens variants if their Cartesian product exceeds the query_max_plans
// flag.
template <typename T>
void LimitPlans(std::vector<std::vector<T>> &variants) {
size_t to_shorten = 0U;
while (CartesianProductSize(variants) > FLAGS_query_max_plans) {
if (variants[to_shorten].size() > 1U) {
variants[to_shorten].pop_back();
}
to_shorten = (to_shorten + 1U) % variants.size();
}
}
// Similar to VaryMatchingStart, but varies the starting nodes for all given
// matchings. After all matchings produce multiple alternative starts, the
// Cartesian product of all of them is returned.
@ -162,6 +204,7 @@ std::vector<std::vector<Matching>> VaryMultiMatchingStarts(
for (const auto &matching : matchings) {
variants.emplace_back(VaryMatchingStart(matching, symbol_table));
}
LimitPlans(variants);
return CartesianProduct<Matching>(variants.cbegin(), variants.cend());
}
@ -232,6 +275,7 @@ std::vector<std::vector<QueryPart>> VaryQueryMatching(
alternative_query_parts.emplace_back(
VaryQuertPartMatching(query_part, symbol_table));
}
LimitPlans(alternative_query_parts);
return CartesianProduct<QueryPart>(alternative_query_parts.cbegin(),
alternative_query_parts.cend());
}