SERVER-17659 Add PlanCacheIndexabilityState

Encapsulates functionality to be used by PlanCache, for deciding how
to cache queries with predicates over elements in partial index key
patterns.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/mongo/db/query/plan_cache_indexability.h b/src/mongo/db/query/plan_cache_indexability.h
new file mode 100644
index 00000000000..aef3a863e98
--- /dev/null
+++ b/src/mongo/db/query/plan_cache_indexability.h
@@ -0,0 +1,87 @@
+/**
+ *    Copyright (C) 2015 10gen Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <vector>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/stdx/functional.h"
+#include "mongo/util/string_map.h"
+
+namespace mongo {
+
+    class BSONObj;
+    class MatchExpression;
+    struct IndexEntry;
+
+    using IndexabilityDiscriminator = stdx::function<bool(const MatchExpression* me)>;
+    using IndexabilityDiscriminators = std::vector<IndexabilityDiscriminator>;
+
+    /**
+     * PlanCacheIndexabilityState holds a set of "indexability discriminators" for certain paths.
+     * An indexability discriminator is a binary predicate function, used to classify match
+     * expressions based on the data values in the expression.
+     */
+    class PlanCacheIndexabilityState {
+        MONGO_DISALLOW_COPYING(PlanCacheIndexabilityState);
+    public:
+        PlanCacheIndexabilityState() = default;
+
+        /**
+         * Gets the set of discriminators associated with 'path'.  Returns an empty set if no
+         * discriminators are registered for 'path'.
+         *
+         * The object returned by reference is valid until the next call to updateDiscriminators()
+         * or until destruction of 'this', whichever is first.
+         */
+        const IndexabilityDiscriminators& getDiscriminators(StringData path) const;
+
+        /**
+         * Clears discriminators for all paths, and regenerate them from 'indexEntries'.
+         */
+        void updateDiscriminators(const std::vector<IndexEntry>& indexEntries);
+
+    private:
+        /**
+         * Adds partial index discriminators for the partial index with the given filter expression
+         * to '_pathDiscriminatorsMap'.
+         *
+         * A partial index discriminator distinguishes expressions that match a given partial index
+         * predicate from expressions that don't match the partial index predicate.  For example,
+         * this allows the predicate {a: {$gt: 5}} to be considered a different shape than the
+         * predicate {a: {$gt: -5}}, if there is a partial index defined with document filter {a:
+         * {$gt: 0}}.  The former is compatible with this index, but the latter is not compatible.
+         */
+        void processPartialIndex(const MatchExpression* filterExpr);
+
+        using PathDiscriminatorsMap = StringMap<IndexabilityDiscriminators>;
+        PathDiscriminatorsMap _pathDiscriminatorsMap;
+    };
+
+}  // namespace mongo