Disable sqlite lookaside buffers by default.

sql/connection.cc

 // 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.
 
 #include "sql/connection.h"
 
 #include <string.h>
 
 #include "base/files/file_path.h"
 #include "base/file_util.h"
@@ skipping 613 matching lines @@
     // Histogram failures specific to initial open for debugging
     // purposes.
     UMA_HISTOGRAM_ENUMERATION("Sqlite.OpenFailure", err & 0xff, 50);
 
     OnSqliteError(err, NULL);
     Close();
     db_ = NULL;
     return false;
   }
 
+  if (!enable_lookaside_buffer_) {
+    // Disable lookaside buffer. Must be run immediatly after opening the
+    // database before any SQL statements are run.
+    sqlite3_db_config(db_, SQLITE_DBCONFIG_LOOKASIDE, NULL, 0, 0);

[Scott Hess - ex-Googler, 2013/06/05 17:58:49]

And maybe buff up the first line of the comment to indicate why it's being done.
 On the order of "SQLite uses a lookaside buffer to improve performance of small
mallocs.  Chromium already depends on small mallocs being efficient, so disable
this."  Or something like that.

[rmcilroy, 2013/06/05 22:24:47]

Done.

+  }
+
   // sqlite3_open() does not actually read the database file (unless a
   // hot journal is found).  Successfully executing this pragma on an
   // existing database requires a valid header on page 1.
   // TODO(shess): For now, just probing to see what the lay of the
   // land is.  If it's mostly SQLITE_NOTADB, then the database should
   // be razed.
   err = ExecuteAndReturnErrorCode("PRAGMA auto_vacuum");
   if (err != SQLITE_OK)
     UMA_HISTOGRAM_ENUMERATION("Sqlite.OpenProbeFailure", err & 0xff, 50);
 
@@ skipping 135 matching lines @@
   // as a single string.  This doesn't appear to be an API contract,
   // it could return separate lines, so loop _and_ split.
   while (stmt.Step()) {
     std::string result(stmt.ColumnString(0));
     base::SplitString(result, '\n', messages);
   }
   return stmt.Succeeded();
 }
 
 }  // namespace sql