How Can I Efficiently Stream Large MySQL Result Sets to Avoid Memory Errors?

Streaming Large Result Sets with MySQL

When working with large tables in MySQL, excessive resource consumption and memory errors can arise due to the default behavior of JDBC drivers loading entire result sets into memory. To mitigate this, it's essential to implement proper techniques for streaming data rather than loading it all at once.

Approach

The provided question suggests using statement.setFetchSize(Integer.MIN_VALUE); to limit data loading, but this alone is insufficient. According to the MySQL JDBC driver documentation, setting the result set to TYPE_FORWARD_ONLY and CONCUR_READ_ONLY is necessary for effective streaming:

stmt = conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_READ_ONLY);
stmt.setFetchSize(Integer.MIN_VALUE);

However, it's crucial to note that this approach has potential drawbacks:

• All rows in the result set must be processed before issuing further queries on the connection.
• Locks are only released once the transaction completes or all results are read or the active result set is closed.

Further Considerations

If setting the result set as TYPE_FORWARD_ONLY and CONCUR_READ_ONLY does not resolve memory issues, the underlying cause may be the storage of data in Java's memory before it's processed. To address this, immediate processing of data as it comes in is required, which might involve significant code modifications. For more information, refer to the provided link in the answer, which addresses a similar issue.

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