SQL execution time much slower in a Tomcat Servlet than in a normal Java program

Question

For inexplicable reasons however, this morning the performance increased for two of my Queries that used to be slow. I have no idea why.
I have no authority over the server, maybe someone changed something.
The problem is no more.

In a nutshell:

• s.executeQuery(sql) runs extremely slowly within a tomcat servlet on server
• Same query runs fine without servlet (simple java program) on the same machine
• Not all queries are slow within the servlet. Only a few bigger ones do
• Same servlet runs fast on another machine

UPDATES

Please read the updates below the text !

I have a servlet that executes SQL requests and sends back the results via JSON. For some reason, some requests take a huge amount of time to execute, but when I run them in any Oracle SQL Client, they are executed in no time.

I am talking about a difference of 1 second vs 5 minutes for the same SQL (that is not that complex).

How can this be explained ? Is there a way to improve the performance of a java based SQL request ?

I am using the traditional way of executing queries:

java.sql.Connection conn = null;
java.sql.Statement s = null;
ResultSet rs = null;

String dbDriver = "oracle.jdbc.driver.OracleDriver";
String dbConnectionString = "jdbc:oracle:thin:@" + dbHost + ":" + dbPort + ":" + dbSid;

Class.forName(dbDriver).newInstance();
conn = DriverManager.getConnection(dbConnectionString, dbUser, dbPass);
s = conn.createStatement();
s.setQueryTimeout(9999);
rs = s.executeQuery(newStatement);
ResultSetMetaData rsmd = rs.getMetaData();

// Get the results
while (rs.next()) {
// collect the results
}

// close connections

I tried with ojdbc14 and ojdbc6 but there was no difference.

UPDATE 1: I tried the same SQL in a local Java project (not a servlet) on my client machine, and I get the results immediately. So I assume the problem is coming from my servlet or the tomcat configuration ?

UPDATE 2: The culprit is indeed rs = s.executeQuery(mySql); I tried to use preparedStatement instead, but there is no difference.

UPDATE 3: I created a new Servlet running on a local Tomcat and the Query comes back fast. The problem is therefore coming from my production server or Tomcat config. Any ideas what config items could affect this ?

UPDATE 4: I tried the same code in a normal java program instead of a servlet (still on the same server) and the results are coming fast. Ergo the problem comes from the Servlet itself (or Tomcat ?). Still don't know what to do, but I narrowed it down :)

UPDATE 5: Jstack shows the following (It starts where my servlet is, I cut the rest)

    "http-8080-3" daemon prio=3 tid=0x00eabc00 nid=0x2e runnable [0xaa9ee000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.read(SocketInputStream.java:129)
        at oracle.net.ns.Packet.receive(Packet.java:311)
        at oracle.net.ns.DataPacket.receive(DataPacket.java:105)
        at oracle.net.ns.NetInputStream.getNextPacket(NetInputStream.java:305)
        at oracle.net.ns.NetInputStream.read(NetInputStream.java:249)
        at oracle.net.ns.NetInputStream.read(NetInputStream.java:171)
        at oracle.net.ns.NetInputStream.read(NetInputStream.java:89)
        at oracle.jdbc.driver.T4CSocketInputStreamWrapper.readNextPacket(T4CSocketInputStreamWrapper.java:123)
        at oracle.jdbc.driver.T4CSocketInputStreamWrapper.read(T4CSocketInputStreamWrapper.java:79)
        at oracle.jdbc.driver.T4CMAREngineStream.unmarshalUB1(T4CMAREngineStream.java:429)
        at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:397)
        at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:257)
        at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:587)
        at oracle.jdbc.driver.T4CStatement.doOall8(T4CStatement.java:210)
        at oracle.jdbc.driver.T4CStatement.doOall8(T4CStatement.java:30)
        at oracle.jdbc.driver.T4CStatement.executeForDescribe(T4CStatement.java:762)
        at oracle.jdbc.driver.OracleStatement.executeMaybeDescribe(OracleStatement.java:925)
        at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(OracleStatement.java:1104)
        at oracle.jdbc.driver.OracleStatement.executeQuery(OracleStatement.java:1309)
        - locked <0xe7198808> (a oracle.jdbc.driver.T4CConnection)
        at oracle.jdbc.driver.OracleStatementWrapper.executeQuery(OracleStatementWrapper.java:422)
        

So i am Stuck at java.net.SocketInputStream.socketRead0(Native Method) ?

Answer 1

In some cases (not sure if this applies to yours) setting fetchSize on the Statement object yields great performance improvements. It depends on the size of the resultSet that is being fetched.

Try playing with it by setting it to something bigger than default 10 for Oracle (see this link).

See Statement.setFetchSize.

Answer 2

Given your symptoms, I believe that your issue is not with your SQL client code and you are in fact looking at issues with your server. The stack shows that your client is waiting for a response. This tallies with the fact that you can run the client without any problem in a separate process.

So what you probably need to look at is systemic reasons why the SQL server is running slowly and how that may be tied to Tomcat. My experience in cases like this is its usually the disk, so I'd be inclined to check whether you are paging due to a lack of RAM when Tomcat is loaded, or suffering from much higher disk ops due to a reduced disk cache. Assuming you are running on a UNIX variant, I'd have a look at vmstat and iostat for a working and broken case to eliminate such issues.