SERVER-2227 Addition of index usage statistics

1 files changed, 116 insertions, 0 deletions

diff --git a/src/mongo/db/collection_index_usage_tracker.h b/src/mongo/db/collection_index_usage_tracker.h
new file mode 100644
index 00000000000..def45712aad
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+++ b/src/mongo/db/collection_index_usage_tracker.h
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+/**
+ *    Copyright (C) 2015 MongoDB 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 "mongo/base/disallow_copying.h"
+#include "mongo/base/string_data.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/util/string_map.h"
+#include "mongo/util/time_support.h"
+
+namespace mongo {
+
+class ClockSource;
+
+/**
+ * CollectionIndexUsageTracker tracks index usage statistics for a collection.  An index is
+ * considered "used" when it appears as part of a winning plan for an operation that uses the
+ * query system.
+ *
+ * Indexes must be registered and deregistered on creation/destruction.
+ */
+class CollectionIndexUsageTracker {
+    MONGO_DISALLOW_COPYING(CollectionIndexUsageTracker);
+
+public:
+    struct IndexUsageStats {
+        IndexUsageStats() = default;
+        explicit IndexUsageStats(Date_t now) : trackerStartTime(now) {}
+
+        IndexUsageStats(const IndexUsageStats& other)
+            : accesses(other.accesses.load()), trackerStartTime(other.trackerStartTime) {}
+
+        IndexUsageStats& operator=(const IndexUsageStats& other) {
+            accesses.store(other.accesses.load());
+            trackerStartTime = other.trackerStartTime;
+            return *this;
+        }
+
+        // Number of operations that have used this index.
+        AtomicInt64 accesses;
+
+        // Date/Time that we started tracking index usage.
+        Date_t trackerStartTime;
+    };
+
+    /**
+     * Constructs a CollectionIndexUsageTracker.
+     *
+     * Does not take ownership of 'clockSource'. 'clockSource' must refer to a non-null clock
+     * source that is valid for the lifetime of the constructed CollectionIndexUsageTracker.
+     */
+    explicit CollectionIndexUsageTracker(ClockSource* clockSource);
+
+    /**
+     * Record that an operation used index 'indexName'. Safe to be called by multiple threads
+     * concurrently.
+     */
+    void recordIndexAccess(StringData indexName);
+
+    /**
+     * Add map entry for 'indexName' stats collection. Must be called under exclusive collection
+     * lock.
+     */
+    void registerIndex(StringData indexName);
+
+    /**
+     * Erase statistics for index 'indexName'. Must be called under exclusive collection lock.
+     * Can be called even if indexName is not registered. This is possible under certain failure
+     * scenarios.
+     */
+    void unregisterIndex(StringData indexName);
+
+    /**
+     * Get the current state of the usage statistics map. This map will only include indexes that
+     * exist at the time of calling. Must be called while holding the collection lock in any mode.
+     */
+    StringMap<CollectionIndexUsageTracker::IndexUsageStats> getUsageStats() const;
+
+private:
+    // Map from index name to usage statistics.
+    StringMap<CollectionIndexUsageTracker::IndexUsageStats> _indexUsageMap;
+
+    // Clock source. Used when the 'trackerStartTime' time for an IndexUsageStats object needs to
+    // be set.
+    ClockSource* _clockSource;
+};
+
+typedef StringMap<CollectionIndexUsageTracker::IndexUsageStats> CollectionIndexUsageMap;
+
+}  // namespace mongo