Question

因此，我的客户端程序运行此代码以获取行数据并在之后将其删除。事情是在SELECT和DELETE之间存在60-130毫秒的延迟，在那个时候另一个客户端可以抓住同一行。有什么办法可以同时进行SELECT和DELETE来阻止这种冲突的发生？

String filterQuery = "SELECT token_id FROM table WHERE expires <= ? LIMIT 1;";

PreparedStatement preparedStmt = conn.prepareStatement(filterQuery);
preparedStmt.setLong(1, System.currentTimeMillis());
long startTime = System.currentTimeMillis();
ResultSet result = preparedStmt.executeQuery();
String token_id = null;
while (result.next()) {
    System.out.println(result.getString(1));
    token_id = result.getString(1);
}

filterQuery = "DELETE FROM table WHERE token_id = ?;";
preparedStmt = conn.prepareStatement(filterQuery);
preparedStmt.setString(1, token_id);
preparedStmt.execute();
System.out.println(System.currentTimeMillis() - startTime+" milliseconds");

Answer 1

如果您希望您的SELECT阻止该行上的后续读取，直到您删除它，那么就如Mark在其注释中所指出的那样，您需要

启用交易（setAutoCommit(false)）
将事务隔离设置为SERIALIZABLE，并且
使用SELECT ... FOR UPDATE

此示例代码对我有用：

conn.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
conn.setAutoCommit(false);

Statement st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT token_id FROM tokens ORDER BY token_id LIMIT 1 FOR UPDATE");
rs.next();
int token_id = rs.getInt("token_id");
System.out.printf("Got %d.%n", token_id);
PreparedStatement ps = conn.prepareStatement("DELETE FROM tokens WHERE token_id=?");
ps.setInt(1, token_id);
ps.executeUpdate();
conn.commit();

Answer 2

由于我误解了XD问题，因此编辑了整个答案

看看mySQL REPEATABLE READ，您的SQ代码将类似于此

SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
START TRANSACTION;
SELECT token_id FROM table WHERE expires <= 'Example';
DELETE FROM table WHERE token_id = 'ExampleID!';
COMMIT;

MySQL-JDBC-同时选择和删除

2 个答案: