History init: add metrics and skip migration.

components/history/core/browser/url_database.cc

 // Copyright 2014 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 "components/history/core/browser/url_database.h"
 
 #include <limits>
 #include <string>
 #include <vector>
 
@@ skipping 568 matching lines @@
   if (GetDB().DoesTableExist(name))
     return true;
 
   // Note: revise implementation for InsertOrUpdateURLRowByID() if you add any
   // new constraints to the schema.
   std::string sql;
   sql.append("CREATE TABLE ");
   sql.append(name);
   sql.append(
       "("
-      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
-      // Using AUTOINCREMENT is for sync propose. Sync uses this |id| as an
-      // unique key to identify the URLs. If here did not use AUTOINCREMENT, and
-      // Sync was not working somehow, a ROWID could be deleted and re-used
+      // The id uses AUTOINCREMENT is for sync propose. Sync uses this |id| as
+      // an unique key to identify the URLs. If here did not use AUTOINCREMENT,
+      // and Sync was not working somehow, a ROWID could be deleted and re-used
       // during this period. Once Sync come back, Sync would use ROWIDs and
       // timestamps to see if there are any updates need to be synced. And sync
-      //  will only see the new URL, but missed the deleted URL.
+      // will only see the new URL, but missed the deleted URL.
+      //
+      // IMPORTANT NOTE: Currently new tables are created with AUTOINCREMENT
+      // but the migration code is disabled. This means that you will not
+      // be able to count on AUTOINCREMENT behavior without adding
+      // additional migration steps.
+      //
+      // Along with this, an unused favicon_id column will exist for tables
+      // without AUTOINCREMENT. This should be removed everywhere.
+      //
+      // TODO(https://crbug.com/736136) figure out how to update users to use
+      // AUTOINCREMENT and remove the favicon_id column consistently.
+      "id INTEGER PRIMARY KEY AUTOINCREMENT,"
       "url LONGVARCHAR,"
       "title LONGVARCHAR,"
       "visit_count INTEGER DEFAULT 0 NOT NULL,"
       "typed_count INTEGER DEFAULT 0 NOT NULL,"
       "last_visit_time INTEGER NOT NULL,"
       "hidden INTEGER DEFAULT 0 NOT NULL)");
+  // IMPORTANT: If you change the colums, also update in_memory_database.cc
+  // where the values are copied (InitFromDisk).
 
   return GetDB().Execute(sql.c_str());
 }
 
 bool URLDatabase::CreateMainURLIndex() {
   return GetDB().Execute(
       "CREATE INDEX IF NOT EXISTS urls_url_index ON urls (url)");
 }
 
 bool URLDatabase::RecreateURLTableWithAllContents() {
@@ skipping 34 matching lines @@
     return false;
 
   const base::Time& real_threshold =
       threshold.is_null() ? AutocompleteAgeThreshold() : threshold;
   return (row.typed_count() >= kLowQualityMatchTypedLimit) ||
          (row.visit_count() >= kLowQualityMatchVisitLimit) ||
          (row.last_visit() >= real_threshold);
 }
 
 }  // namespace history