We have faced some issues with Glassfish's Memory consumption.
See :
1.
https://glassfish.dev.java.net/issues/show_bug.cgi?id=1309
2.
https://glassfish.dev.java.net/issues/show_bug.cgi?id=1771
Both these issues were promptly looked at and fixed.
What i would recommend, is to try to code-in a unit test case that would resemble what is happening in your application as it interacts with Toplink.
Both the bug reports contain source code of the unit test case i created. You can take a look at this source, if it helps you create test cases of your own that resembles your application request that consumes lot of memory.
This kind of test cases make it easy to verify that the bug exists and also clarify that you are using JPA and Toplink in a standard manner.
Additionally having these kind of test cases that validate your assumptions of a third party lib like Toplink will give you confidence when you want to upgrade/switch.
HTH
-Prashant
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