1 // Copyright 2013 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_ 6 #define CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_ 7 8 #include <map> 9 #include <string> 10 11 #include "base/basictypes.h" 12 #include "base/gtest_prod_util.h" 13 14 namespace sql { 15 class Connection; 16 } // namespace sql 17 18 namespace extensions { 19 20 // A class for maintaining a persistent mapping between strings and integers. 21 // This is used to help compress the contents of the activity log database on 22 // disk by replacing repeated strings by smaller integers. 23 // 24 // The mapping from integers to strings is maintained in a database table, but 25 // the mapping is also cached in memory. 26 // 27 // The database table used to store the strings is configurable, but its layout 28 // is fixed: it always consists of just two columns, "id" and "value". 29 // 30 // All calls to DatabaseStringTable must occur on the database thread. 31 class DatabaseStringTable { 32 public: 33 explicit DatabaseStringTable(const std::string& table); 34 35 ~DatabaseStringTable(); 36 37 // Initialize the database table. This will create the table if it does not 38 // exist. Returns true on success; false on error. 39 bool Initialize(sql::Connection* connection); 40 41 // Interns a string in the database table and sets *id to the corresponding 42 // integer. If the string already exists, the existing number is returned; 43 // otherwise, new database row is inserted with the new string. Returns true 44 // on success and false on database error. 45 bool StringToInt(sql::Connection* connection, 46 const std::string& value, 47 int64* id); 48 49 // Looks up an integer value and converts it to a string (which is stored in 50 // *value). Returns true on success. A false return does not necessarily 51 // indicate a database error; it might simply be that the value cannot be 52 // found. 53 bool IntToString(sql::Connection* connection, int64 id, std::string* value); 54 55 // Clears the in-memory cache; this should be called if the underlying 56 // database table has been manipulated and the cache may be stale. 57 void ClearCache(); 58 59 private: 60 // Reduces the size of the cache if too many entries are held in it. 61 void PruneCache(); 62 63 // In-memory caches of recently accessed values. 64 std::map<int64, std::string> id_to_value_; 65 std::map<std::string, int64> value_to_id_; 66 67 // The name of the database table where the mapping is stored. 68 std::string table_; 69 70 FRIEND_TEST_ALL_PREFIXES(DatabaseStringTableTest, Prune); 71 72 DISALLOW_COPY_AND_ASSIGN(DatabaseStringTable); 73 }; 74 75 } // namespace extensions 76 77 #endif // CHROME_BROWSER_EXTENSIONS_ACTIVITY_LOG_DATABASE_STRING_TABLE_H_ 78