Disable sqlite lookaside buffers by default.

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 <map>
 #include <set>
 #include <string>
@@ skipping 122 matching lines @@
   // transaition (requires another access to the DB) and because we don't
   // actually need it.
   //
   // Exclusive mode means that the database is not unlocked at the end of each
   // transaction, which means there may be less time spent initializing the
   // next transaction because it doesn't have to re-aquire locks.
   //
   // This must be called before Open() to have an effect.
   void set_exclusive_locking() { exclusive_locking_ = true; }
 
+
+  // Call to have the database use the default lookaside buffer for small object
+  // allocations. The lookaside buffer is intended to provide a speed boost when
+  // running with slow malloc implementations. However, under typical use-cases
+  // in Chrome, it seem to have no negligible impact while costing 50KB per
+  // connection, therefore we disable it by default.
+  //
+  // This must be called before Open() to have an effect.
+  void set_enable_lookaside_buffer() { enable_lookaside_buffer_ = true; }
+

[Scott Hess - ex-Googler, 2013/06/04 16:35:21]

IMHO, this is either the right thing to do, or not the right thing to do, though
it's possible that the choice differs per-platform.  So exposing this seems like
it's asking for trouble.

[rmcilroy, 2013/06/04 17:05:38]

Done.

   // 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.
   //
   // TODO(shess): ErrorDelegate allowed for returning a different
   // error.  Determine if this is necessary for the callback.  In my
   // experience, this is not well-tested and probably not safe, and
   // current clients always return the same error passed.
@@ skipping 336 matching lines @@
 
   // 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 enable_lookaside_buffer_;
 
   // All cached statements. Keeping a reference to these statements means that
   // they'll remain active.
   typedef std::map<StatementID, scoped_refptr<StatementRef> >
       CachedStatementMap;
   CachedStatementMap statement_cache_;
 
   // A list of all StatementRefs we've given out. Each ref must register with
   // us when it's created or destroyed. This allows us to potentially close
   // any open statements when we encounter an error.
@@ skipping 26 matching lines @@
 
   // Tag for auxiliary histograms.
   std::string histogram_tag_;
 
   DISALLOW_COPY_AND_ASSIGN(Connection);
 };
 
 }  // namespace sql
 
 #endif  // SQL_CONNECTION_H_