我使用 JDBC 连接发出查询:
Connection conn = null
Class.forName("com.mysql.jdbc.Driver")
conn = DriverManager.getConnection(dbHost, dbUser, dbPass)
s = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY);
s.setFetchSize(Integer.MIN_VALUE);
r = s.executeQuery (MY_SELECT_QUERY);
while(...) {
processResultSet(r);
}
while
长时间运行处理 ResultSet。大约 1 小时后,我得到了异常:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 74 milliseconds ago. The last packet sent successfully to the server was 4,351,980 milliseconds ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:407) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3082) at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2968) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3516) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:931) at com.mysql.jdbc.MysqlIO.nextRow(MysqlIO.java:1429) at com.mysql.jdbc.RowDataDynamic.nextRecord(RowDataDynamic.java:416) at com.mysql.jdbc.RowDataDynamic.next(RowDataDynamic.java:395) at com.mysql.jdbc.ResultSetImpl.next(ResultSetImpl.java:7171) at com.busk.indexer.AbstractIndexerClient.indexResultSet(AbstractIndexerClient.scala:34) at com.busk.indexer.ContinousIndexer.startIndexingLoop(ContinousIndexer.scala:18) at com.busk.indexer.IndexerServer$.main(IndexerServer.scala:95) at com.busk.indexer.IndexerServer.main(IndexerServer.scala) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597)
我用谷歌搜索了一下,但几乎所有错误都与连接池有关,并且使用一个连接超过 8 小时(默认的 wait_timeout mysql 设置)。 在我的例子中,我正在处理 ResultSet,我收到了这个错误。
最佳答案
如果发生这种情况是因为结果集中有大量数据,我建议使用“LIMIT s, m”(其中 s - 开始,m - 最大记录 - 均为整数)对响应进行分页。然后在循环中处理此数据,一次处理 1000 条记录的一部分:
boolean finished = false;
int start = 1;
int max = 1000;
do {
r = s.executeQuery (MY_SELECT_QUERY + " LIMIT " + start + ", " + max);
finished = // if r returned less than M records
while(...) {
processResultSet(r);
}
start += // number of returned records;
} while (!finished);
当然,1000 是一个任意数字,您可以尝试找出适合您查询的最佳最大大小。
更新:如果处理每条记录需要很长时间,则将记录存储在一个列表中,并在从数据库中获取所有数据时遍历它们。
关于java - 处理 MySQL 查询花费的时间太长并抛出 "Communications link failure",我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/9949516/