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标题:
mysql connector 执行 select 和 shardingshpere-proxy 的处理过程
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作者:
自由的羽毛
时间:
2023-4-18 17:50
标题:
mysql connector 执行 select 和 shardingshpere-proxy 的处理过程
use java mysql connector
// fake mysql select code
// ... datasource init
Connection conn = datasource.getConnection();
PreparedStatement pst = conn.prepareStatement("select id, task_name from t_task where id = ?");
pst.setLong(1, 31);
pst.executeQuery();
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按照直觉, 既然用了 preparedStatement, 执行过一次后会在服务端缓存好预编译的语句, 之后就能省去这个解析过程,直接提交参数执行就好了
但是, mysql connector 默认创建的是 ClientPreparedStatement
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
try {
synchronized(this.getConnectionMutex()) {
this.checkClosed();
ClientPreparedStatement pStmt = null;
boolean canServerPrepare = true;
String nativeSql = (Boolean)this.processEscapeCodesForPrepStmts.getValue() ? this.nativeSQL(sql) : sql;
if ((Boolean)this.useServerPrepStmts.getValue() && (Boolean)this.emulateUnsupportedPstmts.getValue()) {
canServerPrepare = this.canHandleAsServerPreparedStatement(nativeSql);
}
// useServerPrepStmts = false
if ((Boolean)this.useServerPrepStmts.getValue() && canServerPrepare) {
// ... 省略一些代码
} else {
//... 省略一些代码
pStmt = (ClientPreparedStatement)this.clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
}
} else {
pStmt = (ClientPreparedStatement)this.clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
return (PreparedStatement)pStmt;
}
} catch (CJException var17) {
throw SQLExceptionsMapping.translateException(var17, this.getExceptionInterceptor());
}
}
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因为默认并没有设置 useServerPrepStmts = true, 默认是false 去指定要求服务端缓存 创建的 clientPrepareStatement 客户端语句
是不是 ClientPreparedStatement 看着客户端侧进行一些元数据的缓存?
pst.executeQuery(); 代码中有一段逻辑, 如果cacheResultSetMetadata=true的话,会缓存元数据,但是并没有
boolean cacheResultSetMetadata = (Boolean)locallyScopedConn.getPropertySet().getBooleanProperty(PropertyKey.cacheResultSetMetadata).getValue();
String origSql = ((PreparedQuery)this.query).getOriginalSql();
if (cacheResultSetMetadata) {
cachedMetadata = locallyScopedConn.getCachedMetaData(origSql);
}
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所以,虽然每次还是从服务端拿返回 参数 和 resultSet 的一些元数据
最终发往服务端(这边场景是proxy) 的 sql 其实是非参数化的 com_query 命令
proxy 接收到 com_query 交由 MySQLComQueryPacketExecutor 处理
[code] public Collection
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