[sql] Use memory-mapped I/O for sql::Connection.

sql/connection.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SQL_CONNECTION_H_
 #define SQL_CONNECTION_H_
 
 #include <stdint.h>
 #include <map>
 #include <set>
@@ skipping 128 matching lines @@
   //
   // This must be called before Open() to have an effect.
   void set_exclusive_locking() { exclusive_locking_ = true; }
 
   // Call to cause Open() to restrict access permissions of the
   // database file to only the owner.
   // TODO(shess): Currently only supported on OS_POSIX, is a noop on
   // other platforms.
   void set_restrict_to_user() { restrict_to_user_ = true; }
 
+  // Call to opt out of memory-mapped file I/O.
+  void set_mmap_disabled() { mmap_disabled_ = true; }
+
   // Set an error-handling callback.  On errors, the error number (and
   // statement, if available) will be passed to the callback.
   //
   // If no callback is set, the default action is to crash in debug
   // mode or return failure in release mode.
   typedef base::Callback<void(int, Statement*)> ErrorCallback;
   void set_error_callback(const ErrorCallback& callback) {
     error_callback_ = callback;
   }
   bool has_error_callback() const {
@@ skipping 472 matching lines @@
   // true, autocommit time if the database is not in a transaction, or update
   // time if the database is in a transaction.  Also records change count to
   // EVENT_CHANGES_AUTOCOMMIT or EVENT_CHANGES_COMMIT.
   void RecordTimeAndChanges(const base::TimeDelta& delta, bool read_only);
 
   // Helper to return the current time from the time source.
   base::TimeTicks Now() {
     return clock_->Now();
   }
 
+  // Release page-cache memory if memory-mapped I/O is enabled and the database
+  // was changed.  Passing true for |implicit_change_performed| allows
+  // overriding the change detection for cases like DDL (CREATE, DROP, etc),
+  // which do not participate in the total-rows-changed tracking.
+  void ReleaseCacheMemoryIfNeeded(bool implicit_change_performed);
+
   // The actual sqlite database. Will be NULL before Init has been called or if
   // Init resulted in an error.
   sqlite3* db_;
 
   // Parameters we'll configure in sqlite before doing anything else. Zero means
   // use the default value.
   int page_size_;
   int cache_size_;
   bool exclusive_locking_;
   bool restrict_to_user_;
@@ skipping 21 matching lines @@
   // True if database is open with OpenInMemory(), False if database is open
   // with Open().
   bool in_memory_;
 
   // |true| if the connection was closed using RazeAndClose().  Used
   // to enable diagnostics to distinguish calls to never-opened
   // databases (incorrect use of the API) from calls to once-valid
   // databases.
   bool poisoned_;
 
+  // |true| if SQLite memory-mapped I/O is not desired for this connection.
+  bool mmap_disabled_;
+
+  // |true| if SQLite memory-mapped I/O was enabled for this connection.
+  // Used by ReleaseCacheMemoryIfNeeded().
+  bool mmap_enabled_;
+
+  // Used by ReleaseCacheMemoryIfNeeded() to track if new changes have happened
+  // since memory was last released.
+  int total_changes_at_last_release_;
+
   ErrorCallback error_callback_;
 
   // Tag for auxiliary histograms.
   std::string histogram_tag_;
 
   // Linear histogram for RecordEvent().
   base::HistogramBase* stats_histogram_;
 
   // Histogram for tracking time taken in commit.
   base::HistogramBase* commit_time_histogram_;
@@ skipping 11 matching lines @@
   // Source for timing information, provided to allow tests to inject time
   // changes.
   scoped_ptr<TimeSource> clock_;
 
   DISALLOW_COPY_AND_ASSIGN(Connection);
 };
 
 }  // namespace sql
 
 #endif  // SQL_CONNECTION_H_