How to Stream Large MySQL Result Sets in Spring to Avoid OutOfMemoryError?

Streaming Large Result Sets with MySQL

When dealing with extensive MySQL tables within a Spring application, an OutOfMemoryException can arise as the driver endeavors to load the entire table into memory. Setting statement.setFetchSize(Integer.MIN_VALUE); may not suffice, as this merely provides a hint to the JDBC driver.

To enable streaming of result sets in the MySQL JDBC driver, a more comprehensive approach is required:

1. Create a Statement Instance:

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

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2. Set the Fetch Size:

   stmt.setFetchSize(Integer.MIN_VALUE);

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Cautions:

This method has certain caveats:

• All rows in the result set must be read (or the result set closed) before issuing any further queries on the connection. Failure to do so will result in exceptions.
• Within a transaction, locks are only released once the transaction completes, implying the statement must finish execution first.
• If the OutOfMemoryError persists, the underlying issue may lie in excessive memory usage within the Java code. This necessitates immediate data processing instead of storage.

Additional Insight:

For further strategies on handling large result sets, consider this related question and its answer: [link to similar question].

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