在PreparedStatement中的setFetchSize时,Oracle驱动程序中出现OutOfMemoryError

Question

我有这个代码,这段代码基本上设置了限制,PreparedStatement以避免加载整个表数据.

PreparedStatement pstmt = null;
    ResultSet rs = null;
    try {
        pstmt = con.prepareStatement(sql, ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
        if (getDataSheet().isPagingEnabled()) {
            pstmt.setFetchSize(getDataSheet().getPageSize() + 1);
        }

        if (getDataSheet().isDisableTotalRowsCount() && maxRecords >= 0) {
            if (getDataSheet().isPagingEnabled()) {
                pstmt.setMaxRows(getCurrentPageSize());
            } else {
                pstmt.setMaxRows(maxRecords);
            }
        }

        //the rest of code.

    } catch(Exception ex) {
        //handle exception
    }

这段代码适用于所有数据库供应商,除了Oracle驱动程序中的一个案例,如果我使用setFetchSize了PreparedStatement,并且页面大小超过20000,则驱动程序抛出OutOfMemoryError

Caused by: java.lang.OutOfMemoryError: Java heap space
at oracle.jdbc.driver.PhysicalConnection.getCharBuffer(PhysicalConnection.java:7018)
at oracle.jdbc.driver.OracleStatement.prepareAccessors(OracleStatement.java:907)
at oracle.jdbc.driver.T4CTTIdcb.receiveCommon(T4CTTIdcb.java:261)
at oracle.jdbc.driver.T4CTTIdcb.receive(T4CTTIdcb.java:127)
at oracle.jdbc.driver.T4C8Oall.receive(T4C8Oall.java:992)
at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:194)
at oracle.jdbc.driver.T4CPreparedStatement.executeForDescribe(T4CPreparedStatement.java:791)
at oracle.jdbc.driver.T4CPreparedStatement.executeMaybeDescribe(T4CPreparedStatement.java:866)
at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1186)
at oracle.jdbc.driver.OraclePreparedStatement.executeInternal(OraclePreparedStatement.java:3387)
at oracle.jdbc.driver.OraclePreparedStatement.executeQuery(OraclePreparedStatement.java:3431)
at oracle.jdbc.driver.OraclePreparedStatementWrapper.executeQuery(OraclePreparedStatementWrapper.java:1203)

任何想法为什么在Oracle发生这种情况？有没有想过在DB级别做？提前致谢.

Answer 1

与您的想法相反,setFetchSize不限制检索的记录数量,它确定(或提示)驱动程序应预取和缓存的记录数.MySQL除外,它总是预取所有记录,除非您将获取大小设置为Integer.MIN_VALUE.

驱动程序只是检索了很多行,以至于内存耗尽.