Mattias Lundstrom created DERBY-7123:
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Summary: Opening many client connections at the same time can hang
Key: DERBY-7123
URL: https://issues.apache.org/jira/browse/DERBY-7123
Project: Derby
Issue Type: Bug
Components: JDBC
Affects Versions: 10.15.2.0, 10.14.2.0
Environment: Test run on
$ uname -a
Linux mattiasl-laptop2020 5.8.0-63-generic #71-Ubuntu SMP Tue Jul 13 15:59:12
UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Reporter: Mattias Lundstrom
Attachments: DerbyTest.java
If many connections are opened at the same time towards a Derby network server
using ClientConnectionPoolDataSource.getPooledConnection, then this operation
may hang indefinitely.
This has been tested with network server version 10.14.2.0 and 10.15.2.0 and
the same client versions.
Attached test client program (for 10.15.2.0) to show the behavior. It just
repeatedly tries to open 1000 connections in parallel to the same server (in
the production system, there were much fewer connections, but that makes it is
harder to reproduce). It is generally slow and sometimes seems to hang
indefinitely.
Test can be run by just having a local network server and create a database and
then
{code:java}
$ javac -cp derbyclient.jar:derbytools.jar DerbyTest.java
$ java -cp .:derbyclient.jar:derbytools.jar DerbyTest localhost 1527 seconddb
{code}
(where "seconddb" is the test database)
Testing seems to show that if the getPooledConnection operation is
synchronized, the problem disappears (see commented out code in test program).
We are using this workaround in our application for now.
Running the test program, sometimes the connection seems to hang indefinitely
or at the very least be extremely slow. In these situations neither client nor
server consumes any CPU and the client seems to wait for IO from the server.
Stacktrace from client
{quote}[email protected]/java.net.SocketInputStream.socketRead0(Native Method)
[email protected]/java.net.SocketInputStream.socketRead(SocketInputStream.java:115)
[email protected]/java.net.SocketInputStream.read(SocketInputStream.java:168)
[email protected]/java.net.SocketInputStream.read(SocketInputStream.java:140)
app//org.apache.derby.client.net.Reply.fill(Reply.java:172)
app//org.apache.derby.client.net.Reply.ensureALayerDataInBuffer(Reply.java:216)
app//org.apache.derby.client.net.Reply.readDssHeader(Reply.java:319)
app//org.apache.derby.client.net.Reply.startSameIdChainParse(Reply.java:1085)
app//org.apache.derby.client.net.NetConnectionReply.readExchangeServerAttributes(NetConnectionReply.java:56)
app//org.apache.derby.client.net.NetConnection.readServerAttributesAndKeyExchange(NetConnection.java:764)
app//org.apache.derby.client.net.NetConnection.flowServerAttributesAndKeyExchange(NetConnection.java:708)
app//org.apache.derby.client.net.NetConnection.flowUSRIDONLconnect(NetConnection.java:562)
app//org.apache.derby.client.net.NetConnection.flowConnect(NetConnection.java:359)
app//org.apache.derby.client.net.NetConnection.initialize(NetConnection.java:274)
app//org.apache.derby.client.net.NetConnection.<init>(NetConnection.java:260)
app//org.apache.derby.client.net.ClientJDBCObjectFactoryImpl.newNetConnection(ClientJDBCObjectFactoryImpl.java:327)
app//org.apache.derby.client.ClientPooledConnection.<init>(ClientPooledConnection.java:130)
app//org.apache.derby.client.net.ClientJDBCObjectFactoryImpl.newClientPooledConnection(ClientJDBCObjectFactoryImpl.java:85)
app//org.apache.derby.client.BasicClientDataSource.getPooledConnectionX(BasicClientDataSource.java:1619)
app//org.apache.derby.client.BasicClientDataSource.getPooledConnectionMinion(BasicClientDataSource.java:1560)
app//org.apache.derby.jdbc.ClientConnectionPoolDataSource.getPooledConnection(ClientConnectionPoolDataSource.java:69)
{quote}
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