jdbc预编译缓存加速sql执行
SQL syntax for prepared statements is based on three SQL statements:
-
PREPAREprepares a statement for execution (see Section 13.5.1, “PREPARE Statement” ). -
EXECUTEexecutes a prepared statement (see Section 13.5.2, “EXECUTE Statement” ). -
DEALLOCATE PREPAREreleases a prepared statement (see Section 13.5.3, “DEALLOCATE PREPARE Statement” ).
mysql> PREPARE stmt1 FROM 'SELECT * FROM words where id = ?'; Query OK, 0 rows affected (0.00 sec) Statement prepared mysql> SET @i=1; Query OK, 0 rows affected (0.00 sec) mysql> EXECUTE stmt1 USING @i; Empty set (0.01 sec) mysql> SET @i=2; Query OK, 0 rows affected (0.00 sec) mysql> EXECUTE stmt1 USING @i; +----+------+ | id | word | +----+------+ | 2 | 123 | +----+------+ 1 row in set (0.00 sec) mysql> deallocate prepare stmt1; Query OK, 0 rows affected (0.00 sec) mysql> EXECUTE stmt1 USING @i; ERROR 1243 (HY000): Unknown prepared statement handler (stmt1) given to EXECUTE
MySQL Connector/J
普通的sql执行
@Test
@SneakyThrows
public void testPreCompile() {
String connectString = "jdbc:mysql://localhost/test?user=root&password=toor&useLocalSessionState=true&useSSL=false";
Class.forName("com.mysql.jdbc.Driver")
.newInstance();
try (Connection conn = DriverManager.getConnection(connectString)) {
Stopwatch stopwatch = Stopwatch.createStarted();
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 1);
psts.execute();
stopwatch.stop();
System.out.println("stopwatch = " + stopwatch.elapsed(TimeUnit.MILLISECONDS));
psts.setInt(1, 10);
psts.execute();
}
}
}
wireshark抓包：
mysql general log:
2020-05-04T13:06:07.883131Z 15 Connect root@localhost on test using TCP/IP 2020-05-04T13:06:07.885668Z 15 Query /* mysql-connector-java-8.0.16 (Revision: 34cbc6bc61f72836e26327537a432d6db7c77de6) */SELECT @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@collation_server AS collation_server, @@collation_connection AS collation_connection, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_write_timeout AS net_write_timeout, @@performance_schema AS performance_schema, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@transaction_isolation AS transaction_isolation, @@wait_timeout AS wait_timeout 2020-05-04T13:06:07.905021Z 15 Query SET character_set_results = NULL 2020-05-04T13:06:07.929557Z 15 Query delete from words where id = 1 2020-05-04T13:06:07.934906Z 15 Query delete from words where id = 10 2020-05-04T13:06:07.940645Z 15 Quit
with useServerPrepStmts=true
useServerPrepStmts
Use server-side prepared statements if the server supports them?
Default: false
Since version: 3.1.0
jdbc的连接参数加上 useServerPrepStmts=true ：
首选需要编译statement，请求如下：
后面执行的时候，只传了对应的statement id 1和占位符对应的值 1，大大减少了网络的传输：
mysql的general log如下，也是先prepare， 然后excute了两次， 最后关闭stmt：
2020-05-04T13:15:55.611149Z 16 Connect root@localhost on test using TCP/IP 2020-05-04T13:15:55.615655Z 16 Query /* mysql-connector-java-8.0.16 (Revision: 34cbc6bc61f72836e26327537a432d6db7c77de6) */SELECT @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@collation_server AS collation_server, @@collation_connection AS collation_connection, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_write_timeout AS net_write_timeout, @@performance_schema AS performance_schema, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@transaction_isolation AS transaction_isolation, @@wait_timeout AS wait_timeout 2020-05-04T13:15:55.640086Z 16 Query SET character_set_results = NULL 2020-05-04T13:15:55.672345Z 16 Prepare delete from words where id = ? 2020-05-04T13:15:55.676355Z 16 Execute delete from words where id = 1 2020-05-04T13:15:55.681600Z 16 Execute delete from words where id = 10 2020-05-04T13:15:55.681949Z 16 Close stmt 2020-05-04T13:15:55.687659Z 16 Quit
cachePrepStmts和useServerPrepStmts同时打开
cachePrepStmts
Should the driver cache the parsing stage of PreparedStatements of client-side prepared statements, the “check” for suitability of server-side prepared and server-side prepared statements themselves?
Default: false
Since version: 3.0.10
这里就是加上缓存，stmt close的时候，并不会把之前预编译的stmt给关闭，这个缓存是connection级别的。
@Test
@SneakyThrows
public void testPreCompile() {
String connectString = "jdbc:mysql://localhost/test?user=root&password=toor&useLocalSessionState=true&useSSL=false&useServerPrepStmts=true&cachePrepStmts=true";
Class.forName("com.mysql.jdbc.Driver")
.newInstance();
try (Connection conn = DriverManager.getConnection(connectString)) {
Stopwatch stopwatch = Stopwatch.createStarted();
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 1);
psts.execute();
stopwatch.stop();
System.out.println("stopwatch = " + stopwatch.elapsed(TimeUnit.MILLISECONDS));
psts.setInt(1, 10);
psts.execute();
}
// 上面的stmt关闭之后，再次执行
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 100);
psts.execute();
}
}
// 上面的connection关闭之后，再次执行
try (Connection conn = DriverManager.getConnection(connectString)) {
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 66);
psts.execute();
}
}
}
wireshark抓包：
mysql的general log：
2020-05-04T15:17:32.921041Z 19 Connect root@localhost on test using TCP/IP 2020-05-04T15:17:32.929561Z 19 Query /* mysql-connector-java-8.0.16 (Revision: 34cbc6bc61f72836e26327537a432d6db7c77de6) */SELECT @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@collation_server AS collation_server, @@collation_connection AS collation_connection, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_write_timeout AS net_write_timeout, @@performance_schema AS performance_schema, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@transaction_isolation AS transaction_isolation, @@wait_timeout AS wait_timeout 2020-05-04T15:17:32.949986Z 19 Query SET character_set_results = NULL 2020-05-04T15:17:32.983173Z 19 Prepare delete from words where id = ? 2020-05-04T15:17:32.990498Z 19 Execute delete from words where id = 1 2020-05-04T15:17:32.997115Z 19 Execute delete from words where id = 10 2020-05-04T15:17:32.997566Z 19 Reset stmt 2020-05-04T15:17:32.997725Z 19 Execute delete from words where id = 100 2020-05-04T15:17:33.003682Z 19 Quit 2020-05-04T15:17:33.009206Z 20 Connect root@localhost on test using TCP/IP 2020-05-04T15:17:33.009643Z 20 Query /* mysql-connector-java-8.0.16 (Revision: 34cbc6bc61f72836e26327537a432d6db7c77de6) */SELECT @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@collation_server AS collation_server, @@collation_connection AS collation_connection, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_write_timeout AS net_write_timeout, @@performance_schema AS performance_schema, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@transaction_isolation AS transaction_isolation, @@wait_timeout AS wait_timeout 2020-05-04T15:17:33.010569Z 20 Query SET character_set_results = NULL 2020-05-04T15:17:33.011244Z 20 Prepare delete from words where id = ? 2020-05-04T15:17:33.011475Z 20 Execute delete from words where id = 66 2020-05-04T15:17:33.114892Z 20 Quit
连接关闭之后，重新执行同样的sql，发现又触发了编译。
缓存大小的限制
下面两个参数，分别限制了能够缓存多少个和最大sql的长度
prepStmtCacheSize
prepStmtCacheSize
If prepared statement caching is enabled, how many prepared statements should be cached?
Default: 25
Since version: 3.0.10
prepStmtCacheSqlLimit
If prepared statement caching is enabled, what’s the largest SQL the driver will cache the parsing for?
Default: 256
Since version: 3.0.10
druid 连接池下使用
测试代码：
@Test
@SneakyThrows
public void testPreCompile() {
String connectString = "jdbc:mysql://localhost/test?user=root&password=toor&useLocalSessionState=true&useSSL=false&useServerPrepStmts=true&cachePrepStmts=true";
final DruidDataSource druidDataSource = new DruidDataSource();
druidDataSource.setUrl(connectString);
druidDataSource.setUsername("root");
druidDataSource.setPassword("toor");
druidDataSource.setFilters("slf4j");
// druidDataSource.setTestOnBorrow(true);
// druidDataSource.setTestOnReturn(true);
// druidDataSource.setTestWhileIdle(true);
druidDataSource.setMaxActive(1);
druidDataSource.setInitialSize(1);
druidDataSource.setTimeBetweenLogStatsMillis(900);
try (Connection conn = druidDataSource.getConnection()) {
Stopwatch stopwatch = Stopwatch.createStarted();
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 1);
psts.execute();
stopwatch.stop();
System.out.println("stopwatch = " + stopwatch.elapsed(TimeUnit.MILLISECONDS));
psts.setInt(1, 10);
psts.execute();
}
// 上面的stmt关闭之后，再次执行
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 100);
psts.execute();
}
}
// 上面的connection关闭之后，再次执行
try (Connection conn = druidDataSource.getConnection()) {
try (PreparedStatement psts = conn.prepareStatement("delete from words where id = ?")) {
psts.setInt(1, 66);
psts.execute();
}
}
}
只有一个连接的druid连接池，连接关闭连接时其实是归还到池子中，所以第二次拿连接， 拿到的还是同一个 ；所以没有触发第二次编译。
wireshark抓包：
mysql general log：
2020-05-04T15:21:34.187732Z 21 Connect root@localhost on test using TCP/IP 2020-05-04T15:21:34.202166Z 21 Query /* mysql-connector-java-8.0.16 (Revision: 34cbc6bc61f72836e26327537a432d6db7c77de6) */SELECT @@session.auto_increment_increment AS auto_increment_increment, @@character_set_client AS character_set_client, @@character_set_connection AS character_set_connection, @@character_set_results AS character_set_results, @@character_set_server AS character_set_server, @@collation_server AS collation_server, @@collation_connection AS collation_connection, @@init_connect AS init_connect, @@interactive_timeout AS interactive_timeout, @@license AS license, @@lower_case_table_names AS lower_case_table_names, @@max_allowed_packet AS max_allowed_packet, @@net_write_timeout AS net_write_timeout, @@performance_schema AS performance_schema, @@sql_mode AS sql_mode, @@system_time_zone AS system_time_zone, @@time_zone AS time_zone, @@transaction_isolation AS transaction_isolation, @@wait_timeout AS wait_timeout 2020-05-04T15:21:34.240492Z 21 Query SET character_set_results = NULL 2020-05-04T15:21:34.316483Z 21 Prepare delete from words where id = ? 2020-05-04T15:21:34.333444Z 21 Execute delete from words where id = 1 2020-05-04T15:21:34.344075Z 21 Execute delete from words where id = 10 2020-05-04T15:21:34.351728Z 21 Reset stmt 2020-05-04T15:21:34.352101Z 21 Execute delete from words where id = 100 2020-05-04T15:21:34.356117Z 21 Reset stmt 2020-05-04T15:21:34.356407Z 21 Execute delete from words where id = 66
翻翻源码
jdbc conenctor
prepare的时候，会先从缓存中取：
// com.mysql.cj.jdbc.ConnectionImpl#prepareStatement(java.lang.String, int, int)
@Override
public java.sql.PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
synchronized (getConnectionMutex()) {
checkClosed();
//
// FIXME: Create warnings if can't create results of the given type or concurrency
//
ClientPreparedStatement pStmt = null;
boolean canServerPrepare = true;
String nativeSql = this.processEscapeCodesForPrepStmts.getValue() ? nativeSQL(sql) : sql;
if (this.useServerPrepStmts.getValue() && this.emulateUnsupportedPstmts.getValue()) {
canServerPrepare = canHandleAsServerPreparedStatement(nativeSql);
}
if (this.useServerPrepStmts.getValue() && canServerPrepare) {
if (this.cachePrepStmts.getValue()) {
synchronized (this.serverSideStatementCache) {
// 从cache中取出来
pStmt = this.serverSideStatementCache.remove(new CompoundCacheKey(this.database, sql));
if (pStmt != null) {
// 强转为ServerPreparedStatement，清理参数，直接返回
((com.mysql.cj.jdbc.ServerPreparedStatement) pStmt).setClosed(false);
pStmt.clearParameters();
}
if (pStmt == null) {
// 创建新的ServerPreparedStatement
try {
pStmt = ServerPreparedStatement.getInstance(getMultiHostSafeProxy(), nativeSql, this.database, resultSetType,
resultSetConcurrency);
if (sql.length() < this.prepStmtCacheSqlLimit.getValue()) {
((com.mysql.cj.jdbc.ServerPreparedStatement) pStmt).isCached = true;
}
pStmt.setResultSetType(resultSetType);
pStmt.setResultSetConcurrency(resultSetConcurrency);
} catch (SQLException sqlEx) {
// Punt, if necessary
if (this.emulateUnsupportedPstmts.getValue()) {
pStmt = (ClientPreparedStatement) clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
if (sql.length() < this.prepStmtCacheSqlLimit.getValue()) {
this.serverSideStatementCheckCache.put(sql, Boolean.FALSE);
}
} else {
throw sqlEx;
}
}
}
}
} else {
// only canServerPrepare
try {
pStmt = ServerPreparedStatement.getInstance(getMultiHostSafeProxy(), nativeSql, this.database, resultSetType, resultSetConcurrency);
pStmt.setResultSetType(resultSetType);
pStmt.setResultSetConcurrency(resultSetConcurrency);
} catch (SQLException sqlEx) {
// Punt, if necessary
if (this.emulateUnsupportedPstmts.getValue()) {
pStmt = (ClientPreparedStatement) clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
} else {
throw sqlEx;
}
}
}
} else {
// 正常流程
pStmt = (ClientPreparedStatement) clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
return pStmt;
}
}
ServerPreparedStatement 的继承关系
statement关闭时会重新放入缓存：
// com.mysql.cj.jdbc.ServerPreparedStatement#close
@Override
public void close() throws SQLException {
JdbcConnection locallyScopedConn = this.connection;
if (locallyScopedConn == null) {
return; // already closed
}
synchronized (locallyScopedConn.getConnectionMutex()) {
if (this.isCached && isPoolable() && !this.isClosed) {
clearParameters();
this.isClosed = true;
// 重新缓存起来
this.connection.recachePreparedStatement(this);
return;
}
this.isClosed = false;
realClose(true, true);
}
}
// com.mysql.cj.jdbc.ConnectionImpl#recachePreparedStatement
@Override
public void recachePreparedStatement(JdbcPreparedStatement pstmt) throws SQLException {
synchronized (getConnectionMutex()) {
if (this.cachePrepStmts.getValue() && pstmt.isPoolable()) {
synchronized (this.serverSideStatementCache) {
Object oldServerPrepStmt = this.serverSideStatementCache.put(
new CompoundCacheKey(pstmt.getCurrentCatalog(), ((PreparedQuery<?>) pstmt.getQuery()).getOriginalSql()),
(ServerPreparedStatement) pstmt);
if (oldServerPrepStmt != null && oldServerPrepStmt != pstmt) {
((ServerPreparedStatement) oldServerPrepStmt).isCached = false;
((ServerPreparedStatement) oldServerPrepStmt).setClosed(false);
((ServerPreparedStatement) oldServerPrepStmt).realClose(true, true);
}
}
}
}
}
druid
druid的配置说明中，有如下的介绍，也有了一个更短的名字 PSCache ：
| 配置 | 缺省值 | 说明 |
|---|---|---|
| poolPreparedStatements | false | 是否缓存preparedStatement，也就是 PSCache 。PSCache对支持游标的数据库性能提升巨大，比如说oracle。在mysql下建议关闭。 |
| maxPoolPreparedStatementPerConnectionSize | -1 | 要启用PSCache，必须配置大于0，当大于0时，poolPreparedStatements自动触发修改为true。在Druid中，不会存在Oracle下PSCache占用内存过多的问题，可以把这个数值配置大一些，比如说100 |
看下相关的代码：
// com.alibaba.druid.pool.DruidPooledConnection#closePoolableStatement
public void closePoolableStatement(DruidPooledPreparedStatement stmt) throws SQLException {
PreparedStatement rawStatement = stmt.getRawPreparedStatement();
if (holder == null) {
return;
}
if (stmt.isPooled()) {
try {
rawStatement.clearParameters();
} catch (SQLException ex) {
this.handleException(ex, null);
if (rawStatement.getConnection().isClosed()) {
return;
}
LOG.error("clear parameter error", ex);
}
}
PreparedStatementHolder stmtHolder = stmt.getPreparedStatementHolder();
stmtHolder.decrementInUseCount();
// holder.isPoolPreparedStatements 对应上面配置的开关
if (stmt.isPooled() && holder.isPoolPreparedStatements() && stmt.exceptionCount == 0) {
// 放入缓存池子中
holder.getStatementPool().put(stmtHolder);
stmt.clearResultSet();
holder.removeTrace(stmt);
stmtHolder.setFetchRowPeak(stmt.getFetchRowPeak());
stmt.setClosed(true); // soft set close
} else if (stmt.isPooled() && holder.isPoolPreparedStatements()) {
// the PreparedStatement threw an exception
stmt.clearResultSet();
holder.removeTrace(stmt);
// 开启了PSCache但是这个stmt抛出过异常，直接从缓存中移除
holder.getStatementPool()
.remove(stmtHolder);
} else {
try {
//Connection behind the statement may be in invalid state, which will throw a SQLException.
//In this case, the exception is desired to be properly handled to remove the unusable connection from the pool.
stmt.closeInternal();
} catch (SQLException ex) {
this.handleException(ex, null);
throw ex;
} finally {
holder.getDataSource().incrementClosedPreparedStatementCount();
}
}
}
管理这个cache的最终是 com.alibaba.druid.pool.PreparedStatementPool ，内部是用的 LinkedHashMap 实现的
// com.alibaba.druid.pool.PreparedStatementPool.LRUCache
public class LRUCache extends LinkedHashMap<PreparedStatementKey, PreparedStatementHolder> {
private static final long serialVersionUID = 1L;
public LRUCache(int maxSize){
// 最后一个参数true，保证了是按照访问顺序存储的
// the ordering mode - <tt>true</tt> for access-order,
// <tt>false</tt> for insertion-order
super(maxSize, 0.75f, true);
}
protected boolean removeEldestEntry(Entry<PreparedStatementKey, PreparedStatementHolder> eldest) {
boolean remove = (size() > dataSource.getMaxPoolPreparedStatementPerConnectionSize());
if (remove) {
closeRemovedStatement(eldest.getValue());
}
return remove;
}
}
开启了druid的 poolPreparedStatements ，就不用开启jdbc的相关缓存了; 此外druid还有 sharePreparedStatements 等特性，后面可以接着研究一波。
其他
bug问题
看到一些文章说，这两个参数有bug，专门查了下，大部分是connector的bug，升级即可；server端的bug很少。
聊聊一次与DeadLock的相遇
三、mysql 报错 Unknown type ‘14 in column 3 of 5 in binary-encoded result set - 爱笑的berg - 博客园
是否需要开启
在 浅析MySQL JDBC连接配置上的两个误区 中对这个问题，有比较好的说明:
综上所述，现在在使用MySQL时（如果版本比较新的话），出于性能考虑，应该在数据库连接池上开启针对PreparedStatement的缓存。如果没有使用连接池，或者所用的连接池不支持PSCache，也可以在JDBC连接上设置cachePrepStmts=true。
当然，加上这些参数之后，还是应该观察下系统的监控，看看是否性能有提升。
其中提到了 useConfigs =maxPerformance , 查了下官网：
-- maxPerformance相当于打开了 cachePrepStmts=true cacheCallableStmts=true cacheServerConfiguration=true useLocalSessionState=true elideSetAutoCommits=true alwaysSendSetIsolation=false enableQueryTimeouts=false
类似的还有： solarisMaxPerformance 、 fullDebug 、 coldFusion 等，可以在 MySQL :: MySQL Connector/J 5.1 Developer Guide :: 5.3 Configuration Properties for Connector/J 找到对应的解释。
另外，HikariCP的wiki里也有一篇 MySQL Configuration · brettwooldridge/HikariCP Wiki , 也是建议开启。
参考
- MySQL :: MySQL 5.7 Reference Manual :: 13.5 Prepared Statements
- PreparedStatement是如何大幅度提高性能的 - it610.com
- MySQL Bugs: #24344: useServerPrepStmts impacts time zone calculations
- 浅析MySQL JDBC连接配置上的两个误区
- 聊聊一次与DeadLock的相遇
- 三、mysql 报错 Unknown type ‘14 in column 3 of 5 in binary-encoded result set - 爱笑的berg - 博客园
- 预编译语句(Prepared Statements)介绍，以MySQL为例 - 活在夢裡 - 博客园
- MySQL :: MySQL Connector/J 5.1 Developer Guide :: 5.3 Configuration Properties for Connector/J
- DruidDataSource配置属性列表 · alibaba/druid Wiki
- MySQL :: MySQL Connector/J 8.0 Developer Guide :: 6.3 Configuration Properties
- MySQL Configuration · brettwooldridge/HikariCP Wiki
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