Memory leak in statement cache of PreparedStatement
---------------------------------------------------
Key: DERBY-5415
URL: https://issues.apache.org/jira/browse/DERBY-5415
Project: Derby
Issue Type: Bug
Affects Versions: 10.8.1.2
Environment: Linux, java 1.6.0_27-b07
Reporter: Robert Hoffmann
Priority: Critical
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: 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
...
CASE B:
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;
...
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
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