SQLWarning instances associated with JDBC connections consuming memory in EAP 6

Environment

• Red Hat JBoss Enterprise Application Platform (EAP)
  • 6
  • 7
  • 8
• All Databases

Issue

Reviewing the memory usage histogram/heap for the application, a high volume of memory is associated with SQLWarning instances

Resolution

One or more of the following may be done to address the issue:

• Address the condition identified by the warning so that the warning is no longer raised
• Explicitly clear the warning(s) using the clearWarnings() method for the relevant instance (Connection, PreparedStatement, etc.)
• Allow the connection to timeout and memory will be freed when the connection is closed
• Flush connections as described in How to flush a datasource connection pool in EAP to release their accumulated warnings overhead

Root Cause

• Warnings may be raised by the underlying JDBC driver as the result of activity using connections, statements and result sets
• Because connections and statements (specifically PreparedStatement instances which are cached by connections) may have a long life cycle, memory may accumulate if not explicitly cleared

Diagnostic Steps

Obtain a heap dump and confirm:

• The text of the warning(s)
• The class which directly owns the warnings (e.g. a class implementing Connection, PreparedStatement, ResultSet, etc.)
  • Since connections "own" statements and statements "own" result sets, memory associated with one may impact the retained heap of others

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