[DERBY-5415] Memory leak in statement cache of PreparedStatement

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 10.5.3.0, 10.7.1.1, 10.8.1.2
• Component/s: JDBC, Services
• Labels: derby_triage10_9
• Environment: Linux, java 1.6.0_27-b07
• Urgency: Normal
• Issue & fix info: Repro attached
• Bug behavior facts: Performance
• Assignee: Unassigned
• Reporter: Robert Hoffmann
• Created: 16/Sep/11 12:57
• Updated: 01/Mar/12 01:26

Description

Hi,

I) Description

When making thousands of simple queries to one table using PreparedStatement, I have noticed quickly increasing memory usage (hundreds of MB within a few dozens of seconds): CASE A.

I found that memory usage is NORMAL when I keep the PreparedStatement OPEN for all queries (CASE B).

CASE A ("Closing and preparing statement -> leaking"):
>>
while(true) {
PreparedStatement ps = con.prepareStatement("SELECT * from t where a=?");
ps.setInt(1, r);

ResultSet rs = ps.executeQuery();
while (rs.next())

{ rs.getInt("b"); }
rs.close();
ps.close();
}
<<

CASE B ("Keep prepared statement open -> steady memory"):
>>
PreparedStatement ps = con.prepareStatement("SELECT * from t where a=?");

while(true) {
ps.setInt(1, r);

ResultSet rs = ps.executeQuery();
while (rs.next()) { rs.getInt("b"); }

rs.close();
// keep open: ps.close(); // close later
}
<<

II) Reproducibility and heap histogram

I can easily reproduce this problem in our production environment. And the heap of both cases is very distinct:

CASE A:
num #instances #bytes class name
----------------------------------------------
1: 1133492 57289984 [Ljava.lang.Object;
2: 1035688 53548872 [C
3: 249501 33051904 [I
4: 152208 21917952 org.apache.derby.impl.jdbc.EmbedPreparedStatement40
5: 59773 20561912 org.apache.derby.impl.sql.execute.BulkTableScanResultSet
6: 750585 18014040 java.util.ArrayList
7: 674840 16196160 java.lang.String
8: 989684 15834944 org.apache.derby.iapi.types.SQLInteger
9: 391939 15677560 org.apache.derby.impl.sql.GenericParameter
10: 538700 14375272 [Lorg.apache.derby.iapi.types.DataValueDescriptor;
11: 59775 13389600 org.apache.derby.impl.sql.execute.IndexRowToBaseRowResultSet
12: 59775 12433200 org.apache.derby.impl.sql.execute.ProjectRestrictResultSet
13: 59775 9085800 org.apache.derby.impl.store.access.btree.index.B2IForwardScan
14: 179325 8607600 org.apache.derby.impl.store.raw.data.BaseContainerHandle
15: 351721 8441304 java.util.HashMap$Entry
16: 239117 7651744 java.util.HashMap$KeyIterator
17: 59775 6694800 org.apache.derby.impl.jdbc.EmbedResultSet40
18: 239119 5738856 org.apache.derby.impl.store.access.heap.HeapRowLocation
19: 179325 5738400 org.apache.derby.impl.store.access.conglomerate.OpenConglomerateScratchSpace
20: 119550 5738400 org.apache.derby.impl.store.access.heap.OpenHeap
21: 119548 5738240 [[Lorg.apache.derby.iapi.types.DataValueDescriptor;
...

CASE B:

num #instances #bytes class name
----------------------------------------------
1: 224186 9471600 [C
2: 21030 8223200 [I
3: 105020 5553016 [Ljava.lang.Object;
4: 43650 4931368 <constMethodKlass>
5: 201157 4827768 java.lang.String
6: 174474 4187376 java.util.HashMap$Entry
7: 43650 3846512 <methodKlass>
8: 7654 3317816 [B
9: 65633 2663504 <symbolKlass>
10: 16143 2481304 [Ljava.util.HashMap$Entry;
11: 3442 2056408 <constantPoolKlass>
12: 79290 1902960 java.util.ArrayList
13: 3442 1554272 <instanceKlassKlass>
14: 45596 1459072 org.apache.derby.impl.store.raw.data.StoredRecordHeader
15: 2890 1281888 <constantPoolCacheKlass>
16: 25536 1225728 at.intelservice.ie.IS_SText$SIsland
17: 45566 1093584 org.apache.derby.impl.store.raw.data.RecordId
18: 28649 916768 java.util.LinkedHashMap$Entry
19: 1795 734400 [Lorg.apache.derby.impl.store.raw.data.StoredRecordHeader;
20: 4025 611800 org.apache.derby.impl.store.access.btree.index.B2IForwardScan
21: 14614 584560 java.util.HashMap
22: 12075 579600 org.apache.derby.impl.store.raw.data.BaseContainerHandle
23: 34005 544080 java.lang.Integer
24: 4817 539504 org.apache.derby.impl.jdbc.EmbedResultSet40
...

III) Simple test app
Unfortunately, I am unable to create a simple test that would work on my desktop. However if I set derby.language.statementCacheSize=0 then I get a similar phenotype as on our production server (i.e. CASE A).

IV) Workaround
Right now I am keeping the PreparedStatement open as a workaround but I am afraid this might lead to other problems.

I hope this will help you to make Derby even better!

Thank you very much for this great product and best regards,

Robert