SERVER-28300 Implement the logical session cache

1 files changed, 159 insertions, 0 deletions

diff --git a/src/mongo/db/logical_session_cache.h b/src/mongo/db/logical_session_cache.h
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+++ b/src/mongo/db/logical_session_cache.h
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+/**
+ *    Copyright (C) 2017 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/status_with.h"
+#include "mongo/db/logical_session_id.h"
+#include "mongo/db/logical_session_record.h"
+#include "mongo/db/service_liason.h"
+#include "mongo/db/sessions_collection.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/stdx/thread.h"
+#include "mongo/util/lru_cache.h"
+
+namespace mongo {
+
+/**
+ * A thread-safe cache structure for logical session records.
+ *
+ * The cache takes ownership of the passed-in ServiceLiason and
+ * SessionsCollection helper types.
+ */
+class LogicalSessionCache {
+public:
+    using SessionList = std::list<LogicalSessionId>;
+
+    static constexpr int kLogicalSessionCacheDefaultCapacity = 10000;
+    static constexpr Minutes kLogicalSessionDefaultTimeout = Minutes(30);
+    static constexpr Minutes kLogicalSessionDefaultRefresh = Minutes(5);
+
+    /**
+     * An Options type to support the LogicalSessionCache.
+     */
+    struct Options {
+        Options(){};
+
+        /**
+         * The number of session records to keep in the cache.
+         */
+        int capacity = kLogicalSessionCacheDefaultCapacity;
+
+        /**
+         * A timeout value to use for sessions in the cache, in minutes.
+         *
+         * By default, this is set to 30 minutes.
+         */
+        Minutes sessionTimeout = kLogicalSessionDefaultTimeout;
+
+        /**
+         * The interval over which the cache will refresh session records.
+         *
+         * By default, this is set to every 5 minutes. If the caller is
+         * setting the sessionTimeout by hand, it is suggested that they
+         * consider also setting the refresh interval accordingly.
+         */
+        Minutes refreshInterval = kLogicalSessionDefaultRefresh;
+    };
+
+    /**
+     * Construct a new session cache.
+     */
+    explicit LogicalSessionCache(std::unique_ptr<ServiceLiason> service,
+                                 std::unique_ptr<SessionsCollection> collection,
+                                 Options options = Options{});
+
+    LogicalSessionCache(const LogicalSessionCache&) = delete;
+    LogicalSessionCache operator=(const LogicalSessionCache&) = delete;
+
+    ~LogicalSessionCache();
+
+    /**
+     * Returns the owner for the given session, or return an error if there
+     * is no authoritative record for this session.
+     *
+     * If the cache does not already contain a record for this session, this
+     * method may issue networking operations to obtain the record. Afterwards,
+     * the cache will keep the record for future use.
+     *
+     * This call will promote any record it touches to be the most-recently-used
+     * record in the cache.
+     */
+    StatusWith<LogicalSessionRecord::Owner> getOwner(LogicalSessionId lsid);
+
+    /**
+     * Returns the owner for the given session if we already have its record in the
+     * cache. Do not fetch the record from the network if we do not already have it.
+     *
+     * This call will promote any record it touches to be the most-recently-used
+     * record in the cache.
+     */
+    StatusWith<LogicalSessionRecord::Owner> getOwnerFromCache(LogicalSessionId lsid);
+
+    /**
+     * Inserts a new authoritative session record into the cache. This method will
+     * insert the authoritative record into the sessions collection. This method
+     * should only be used when starting new sessions and should not be used to
+     * insert records for existing sessions.
+     */
+    Status startSession(LogicalSessionRecord authoritativeRecord);
+
+    /**
+     * Removes all local records in this cache. Does not remove the corresponding
+     * authoritative session records from the sessions collection.
+     */
+    void clear();
+
+private:
+    /**
+     * Internal methods to handle scheduling and perform refreshes for active
+     * session records contained within the cache.
+     */
+    void _refresh();
+
+    /**
+     * Returns true if a record has passed its given expiration.
+     */
+    bool _isDead(const LogicalSessionRecord& record, Date_t now) const;
+
+    /**
+     * Takes the lock and inserts the given record into the cache.
+     */
+    boost::optional<LogicalSessionRecord> _addToCache(LogicalSessionRecord record);
+
+    const Minutes _refreshInterval;
+    const Minutes _sessionTimeout;
+
+    std::unique_ptr<ServiceLiason> _service;
+    std::unique_ptr<SessionsCollection> _sessionsColl;
+
+    stdx::mutex _cacheMutex;
+    LRUCache<LogicalSessionId, LogicalSessionRecord, LogicalSessionId::Hash> _cache;
+};
+
+}  // namespace mongo