Query caching boosts the performance of PHP MySQL applications. Caching can be done on the database server or at the web clients. The mysqlnd plugin adds query caching to all PHP MySQL extension! It is fast, transparent and supports Memcache, APC, SQLite. Learn how to use its rich sets of performance statistics and how to identify cache candidates.

1. MySQL native driver for PHP: Dig deeper with QC statistics

2. mysqlnd_qc: Dig deeper with statistics Ulf Wendel, Andrey Hristov MySQL Connectors Team Sun Microsystems

5. Storage handler statistic

6. Tuning screws (statistics) all over mysqlnd, mysqlnd_qc core, mysqlnd_qc storage handler <?php /* Any PHP MySQL application */ ?> ext/*mysql* ext/*mysql* mysqlnd mysqlnd Query Cache Plugin (mysqlnd_qc core) Storage handler (mysqlnd_qc)

9. Connection: mysqli_get_connection_stats()

11. Result set related

12. Connection related

13. Client-Server Protocol related

17. Network related

18. Timings

22. Cache related e.g. hit, miss, added, occurences...

23. Timings

26. mysqlnd_qc_get_cache_info()

28. APC: timings, hit ratio, result set size

29. Default: like APC plus result set meta data

30. Runtime configuration

33. Storage handler statistic

35. Check cache hit/miss ratio

36. Check how many queries get cached

39. Accessing core statistics Change runtime configuration to collect statistics! array mysqlnd_qc_get_core_statistics() Returns a list of statistics collected by the core of the query cache plugin, if the PHP configuration setting mysqlnd_qc_collect_statistics is set to 1. The statistics are provided by the core and therefore available with all build-in storage handlers and when using user-defined storage handlers.

42. use of gettimeofday() system call

44. enable/disable: slam_stale_*

46. Aggregated for all PHP MySQL extensions: ext/mysql, ext/mysqli, PDO_MySQL

47. Aggregated for all cache entries

48. Watch out when interpreting the figures – different processes may show different figures!

51. Files

52. Network

53. Memcache, APC, ...

54. Manual aggregation using MySQL Fire and forget - works well for all kinds of QC stats! array mysqlnd_qc_get_core_statistics() Returns a list of statistics collected by the core of the query cache plugin, if the PHP configuration setting mysqlnd_qc_collect_statistics is set to 1. The statistics are provided by the core and therefore available with all build-in storage handlers and when using user-defined storage handlers.

56. … and cached data has been reused

57. … and we had a miss but the statement got cached by someone else while we process it

59. .. and has been added to cache right now

60. ...but cache_no_table = 1 prevented caching

61. ...but unbuffered result set used

64. Take care when calculating derived statistics. Handler with a storage life time beyond process scope may report cache_put = 0 together with cache_hit > 0, if another process has filled the cache. You may want to use “num_entries” from mysqlnd_cache_info(), given the handler supports it (Default, APC).

69. A value >0 indicates storage issues (errors, cache full, … - details are unknown)

71. … and statement executed without errors

72. … and meta data shows at least one column

73. It may or may not be in the cache already

74. It may or may not be added to cache later on

76. … and we have found it in the cache ...

77. … but we have not yet replayed cached data

78. No cache hit yet: client might not fetch data

79. No cache hit yet: cached data may be faulty

81. … it may or may not be in the cache already

82. … but either replaying cached data failed, no result set is available or some other error happened

94. This is the total amount of incoming traffic saved by using the query cache plugin

97. This is the total amount of outgoing traffic saved by using the query cache plugin

102. Storage handler statistic

103. Query back trace php.ini setting: mysqlnd_qc.collect_query_trace = 1 array mysqlnd_qc_get_query_trace_log() Returns a list query back traces for every query that has been inspected by the query cache regardless if the query ended up being cached or not. The trace tells you where a query has been issues (see also debug_backtrace()). Together with the back trace you get run and store times and information on if the query has been cached.

106. limits code back trace depth

108. Data from all PHP MySQL APIs: ext/mysql, ext/mysqli, PDO_MySQL

110. Trace contains all inspected queries

111. Trace contains cached and uncached queries

113. Back trace to the origin of the query

114. Back trace begins with, e.g. mysqli_query()

115. ini setting: mysqlnd_qc.query_trace_bt_depth

117. ini setting: mysqlnd_qc.time_statistics

119. ini setting: mysqlnd_qc.time_statistics

120. (enabled by default)

122. Set to true if the query qualifies for caching

123. according to the query analysis

125. Set to true if any column from the result set

126. has no table name, e.g. SELECT NOW()

128. Set to true if the query has been added to the

130. Set to true in case of a cache hit.

131. Normalized query back trace mysqlnd_qc.collect_normalized_query_trace = 1 array mysqlnd_qc_get_normalized_query_trace_log() Similar to mysqlnd_qc_get_query_trace_log() but with SQL statements normalized and aggregated by the normalized query string. Normalization refers to replacing actual parameters, for example in “WHERE a > 1”, with questionmarks like “ WHERE a > ?”. “WHERE a > ?” will match any value for “?”, for example “1”, “2”, “'abc'” but not other identifiers.

133. enable/disable normalized query trace

135. Data from all PHP MySQL APIs: ext/mysql, ext/mysqli, PDO_MySQL

136. Aggregated by normalized query

138. Trace contains all inspected queries

139. Aggregated by normalized SQL statement

140. Normalized: parameter replaced by placeholder

142. Number of SQL statements summarized

143. in this record set

145. Set to true if the query qualifies for caching

146. according to the query analysis

147. The query might or might not be cached

149. avg_run_time

151. Minimum, average and maximum run time of all queries aggregated in this record set

152. ini setting: mysqlnd_qc.time_statistics

153. (enabled by default)

155. avg_store_time

157. Minimum, average and maximum store time of all queries aggregated in this record set

158. ini setting: mysqlnd_qc.time_statistics

159. (enabled by default)

162. Access statistics

164. Accessing storage handler statistics User storage handler need to provide their own API! array mysqlnd_qc_get_cache_info() Returns information on the active handler and, if available, storage handler statistics. Storage handler statistics are provided under the “data” key of the hash. Different storage handler return different statistics, if any. User defined storage handler cannot return their statistics through this function. They need to provide their own API for accessing storage handler level statistics.

166. Set mysqlnd_qc.time_statistics = 1

168. Default and APC handler provide meta data

169. Search and account table names from meta data

170. Analyze recorded run and store times

172. Set mysqlnd_qc.collect_statistics = 1

173. Set mysqlnd_qc.time_statistics = 1

174. Read user handler specific presentation! :-)

177. enable/disable: all timings

178. background: handler make use of core function

180. APC: machine (multiple processes)

181. Data from all PHP MySQL APIs: ext/mysql, ext/mysqli, PDO_MySQL

183. added to the cache

184. See http://blog.ulf-wendel.de/?p=198 for

185. high-level discussion of the raw network format

188. Set once when adding the query to the cache

190. avg_run_time

192. time measured during a cache hit

194. avg_store_time

196. time measured during a cache hit

199. Set once when adding the query to the cache

201. avg_run_time

202. max_run_time

203. min_store_time

204. avg_store_time

206. NULL if no cache hit

208. Demonstrates usage of statistics

209. Not a production level tool

211. Per-process statistics

212. Cache contents (storage handler statistics)

213. Per-machine statistics using slow auto_append example script

215. auto_append to persist per-process data

216. Demonstrates aggregation of core statistics

218. MySQL storage only

219. The End Feedback: ulf.wendel@sun.com The End Feedback: [email_address] , [email_address]