Add a field trial for using lower sqlite cache sizes.

chrome/browser/history/text_database.cc

 // Copyright (c) 2011 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 <limits>
 #include <set>
 #include <string>
 
 #include "chrome/browser/history/text_database.h"
 
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/metrics/histogram.h"
 #include "base/string_number_conversions.h"
 #include "base/stringprintf.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/diagnostics/sqlite_diagnostics.h"
+#include "chrome/browser/history/history_field_trial.h"
 #include "sql/statement.h"
 #include "sql/transaction.h"
 
 // There are two tables in each database, one full-text search (FTS) table which
 // indexes the contents and title of the pages. The other is a regular SQLITE
 // table which contains non-indexed information about the page. All columns of
 // a FTS table are indexed using the text search algorithm, which isn't what we
 // want for things like times. If this were in the FTS table, there would be
 // different words in the index for each time number.
 //
@@ skipping 103 matching lines @@
   // Set the database page size to something a little larger to give us
   // better performance (we're typically seek rather than bandwidth limited).
   // This only has an effect before any tables have been created, otherwise
   // this is a NOP. Must be a power of 2 and a max of 8192.
   db_.set_page_size(4096);
 
   // The default cache size is 2000 which give >8MB of data. Since we will often
   // have 2-3 of these objects, each with their own 8MB, this adds up very fast.
   // We therefore reduce the size so when there are multiple objects, we're not
   // too big.
-  db_.set_cache_size(512);
+  if (HistoryFieldTrial::IsLowMemFieldTrial()) {
+    // FTS does merges of 16 pages at a time, so we need a working set size
+    // somewhat greater than that to prevent too much thrashing.
+    db_.set_cache_size(40);
+  } else {
+    db_.set_cache_size(512);

[jar (doing other things), 2011/10/24 18:40:55]

Rather than having exactly two choices, have you consider a ew choices in a
range, each in a field trial group?  The sizes you chose differ by more than an
order of magnitude, and I'm guessing you're curious about where the optimum
paramaters are.  I'm not suggesting 50... but perhaps 3-5??

[Scott Hess - ex-Googler, 2011/10/24 19:15:27]

Wait - from our chat I thought this was 32, which is why I suggested that it
might want to be raised a little.  I'm less confident going from 512 to 40.

[brettw, 2011/10/25 01:55:02]

How about I'll change this to 128. Depending on what those histograms look like,
we'll try some lower values in the future.

[Scott Hess - ex-Googler, 2011/10/26 21:44:59]

OK, seems reasonable.

One "thing" about having just two values is we won't know the shape of the
curve.  You will get some threshold information (is it too horrible to keep or
not), but you probably won't get any info about how 64 or 256 will work.  Of
course, it's entirely possible that 128, 256 and 512 would all have the same
results, in which case more than two also won't tell you anything!  [That's a
happy result, actually.]

+  }
 
   // Run the database in exclusive mode. Nobody else should be accessing the
   // database while we're running, and this will give somewhat improved perf.
   db_.set_exclusive_locking();
 
   // Attach the database to our index file.
   if (!db_.Open(file_name_))
     return false;
 
   // Meta table tracking version information.
@@ skipping 223 matching lines @@
   } else {
     // Since we got the results in order, we know the last item is the last
     // time we considered.
     *first_time_searched = results->back().time;
   }
 
   statement.Reset();
 }
 
 }  // namespace history