Memory Leak when fetching Temporary LOBS using Entity Manager Native Query

[hanem42]

Issue
Executing an Oracle native SQL query via EclipseLink JPA that applies SUBSTR to a CLOB column and returns the result as a String causes steady heap growth over time. Heap dumps show retained objects rooted in oracle.jdbc.driver.T4CConnection, specifically the protected field:

HashMap<OracleLargeObject, String> temporaryLobs

With repeated query execution, the temporaryLobs map grows and entries are not released/cleared, leading to increased heap usage and eventual OOM under sustained load. Looks like temporary LOB tracking is not being cleaned up after result processing/statement completion in the EclipseLink native query execution path.

Evidence

• Heap dump / object histogram shows increasing retained size from oracle.jdbc.driver.T4CConnection.temporaryLobs and associated OracleLargeObject instances.
• Growth correlates directly with repeated execution of the native query shown below.

Class Name	Shallow Heap	Retained Heap	Percentage
oracle.jdbc.driver.T4CConnection @ 0x6037fddf0	1,944	5,18,52,152	43.35%
|- temporaryLobs java.util.HashMap @ 0x6038dde80	48	5,14,32,832	43.00%
|- tempLobRefCount java.util.Hashtable @ 0x6038e4638	48	3,29,216	0.28%
|- oracle.net.ns.SessionAtts @ 0x6037f71e0	232	20,288	0.02%
|- connectionBufferCacheStore oracle.jdbc.driver.PhysicalConnection$BufferCacheStore @ 0x606c34098	24	19,984	0.02%
|- auth oracle.jdbc.driver.T4CTTIoauthenticate @ 0x6038df880	200	7,512	0.01%
|- methodTempLargeByteBuffer byte[4096] @ 0x6037fe768	4,112	4,112	0.00%
|- oracle.jdbc.driver.T4CPreparedStatement @ 0x605f15920	968	3,640	0.00%
|- sessionPropertiesCopy java.util.Properties @ 0x6038dc558	56	3,272	0.00%
|- statements oracle.jdbc.driver.T4CPreparedStatement @ 0x606c93218	968	3,024	0.00%
|- tempLobsToFree byte[2048] @ 0x6038e3888	2,064	2,064	0.00%
|- net oracle.net.ns.NSProtocolNIO @ 0x6037f72c8	48	1,872	0.00%
|- oracle.jdbc.driver.Accessor[1] @ 0x606c935e0	24	1,264	0.00%
|- statementCache oracle.jdbc.driver.LRUStatementCache @ 0x608bfb4f0	40	1,216	0.00%
|- oracle.net.nt.ConnOption @ 0x6037f73a0	152	848	0.00%
|- all8 oracle.jdbc.driver.T4C8Oall @ 0x6038e17d8	240	736	0.00%
|- okeyval oracle.jdbc.driver.T4CTTIokeyval @ 0x6038e2aa0	112	704	0.00%
|- java.util.Properties @ 0x6037f7710	56	696	0.00%
|- pipeline oracle.jdbc.driver.Pipeline @ 0x6038e4228	72	688	0.00%
|- driverResources oracle.jdbc.driver.resource.DriverResources @ 0x6037f7f08	16	640	0.00%
|- oaqenq oracle.jdbc.driver.T4CTTIoaqenq @ 0x6038e1ea8	168	504	0.00%
|- aqe oracle.jdbc.driver.T4Caqe @ 0x6038e1b38	160	456	0.00%
|- osaga oracle.jdbc.driver.T4CTTIosaga @ 0x6038e3698	152	448	0.00%
|- aqdq oracle.jdbc.driver.T4Caqdq @ 0x6038e1cf8	144	440	0.00%
|- oaqdeq oracle.jdbc.driver.T4CTTIoaqdeq @ 0x6038e20a0	144	440	0.00%
'- sun.nio.ch.SocketChannelImpl @ 0x6037f74f8 connected local=10.3.10.111:61503 remoteAddress=faeops-oci-cman.oraclecorp.com/138.3.98.170:1999	120	432	0.00%

To Reproduce
Steps/resources to reproduce the behavior:

• EclipseLink version: 4.0.7
• Java/JDK: 21
• Database: Oracle Database
• JDBC driver: ojdbc11-23.7.0.25.01
• JPA usage: EntityManager.createNativeQuery(...) returning scalar String
• Connection pooling: UCP

Try to query a table with a CLOB column containing text data (at least >4000 chars) repeatedly from app

...
for (int i = 0; i < 2_000; i++) {
    Query q = em.createNativeQuery(
        "select substr(CLOB_COL, 1, 5000) as CLOB_COL " +
        "from TABLE_NAME where ID = ?1"
    );
    q.setParameter(1, 1L);

    List<String> rs = q.getResultList();
    String s = rs.isEmpty() ? null : rs.get(0);
}
...

How to observe

• During the run take heap dumps periodically.
• In the heap dump, inspect retained references from oracle.jdbc.driver.T4CConnection and check growth in temporaryLobs.

Expected behavior
Temporary LOB bookkeeping should be released/cleared after result processing and statement completion. Heap usage should remain stable during repeated execution; oracle.jdbc.driver.T4CConnection.temporaryLobs should not grow unbounded.

Additional context
Running the same SQL repeatedly using direct JDBC (PreparedStatement + close ResultSet/Statement) does not show growth in temporaryLobs/

[mittuthomas]

+1