Java process high CPU

Question

Below is my code and thread dump. I've no clue on why the CPU goes 100%. Anybody can help here ? The below method is the suspect ,I'm just trying to parse a result set and write it to csv with Apache CSV (commons-csv-1.5.jar). When i comment the line invoking this method, cpu remains at 3%.

public static void writeResultSetToFile(ResultSet resultSet, String fileName) {

    BufferedWriter writer = null;
    CSVPrinter csvPrinter = null;

    //If the file with the same filename already exist, a date stamp is appended to the end of the file.
    if(checkIfFileExist(fileName)) {
        LOGGER.info("FILE EXIST:"+fileName);
        String fileNamePostFix = new SimpleDateFormat(Constants.FORMAT_yyyyMMddHHmm).format(new Date());
        fileName=fileName.concat(Constants.UNDERSCORE).concat(fileNamePostFix);
        LOGGER.info("WRITING TO FILE: "+fileName);
    }

    try {
        ResultSetMetaData metadata = resultSet.getMetaData();
        writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileName),StandardCharsets.UTF_8));

        //Fetch the column header from the metadata and inserts to an arrayList
        columnCount = metadata.getColumnCount();
        List<String> headerList = new ArrayList<String>(0);
        for (int i = 1; i <= columnCount; i++) {
            headerList.add(metadata.getColumnName(i));
        }
        String[] headerArray = new String[headerList.size()];
        headerArray = headerList.toArray(headerArray);

        //Creates a csv printer with the column names fetched from the database 
        csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT.withHeader(headerArray).withDelimiter(Constants.C_DELIMITER));

        recordCount = 0;
        List<String> valueList = new ArrayList<String>(0);
        while (resultSet.next()) {
            recordCount++;
            for (int i = 1; i <= columnCount; i++) {
                valueList.add(resultSet.getString(i));
            }
            csvPrinter.printRecord(valueList);
            valueList = new ArrayList<String>(0);
        }

    } catch (SQLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    finally {
        if (writer != null) {
            try {
                writer.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (csvPrinter != null) {
            try {
                csvPrinter.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

THREAD DUMP

Full thread dump OpenJDK 64-Bit Server VM (24.171-b01 mixed mode):

"pool-2-thread-1" prio=10 tid=0x00007f2eb839d000 nid=0x264e runnable [0x00007f2ea6dc4000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.read(SocketInputStream.java:153)
        at java.net.SocketInputStream.read(SocketInputStream.java:122)
        at java.io.BufferedInputStream.fill(BufferedInputStream.java:235)
        at java.io.BufferedInputStream.read1(BufferedInputStream.java:275)
        at java.io.BufferedInputStream.read(BufferedInputStream.java:334)
        - locked <0x00000000e01bc220> (a java.io.BufferedInputStream)
        at org.apache.thrift.transport.TIOStreamTransport.read(TIOStreamTransport.java:127)
        at org.apache.thrift.transport.TTransport.readAll(TTransport.java:84)
        at org.apache.thrift.transport.TSaslTransport.readLength(TSaslTransport.java:346)
        at org.apache.thrift.transport.TSaslTransport.readFrame(TSaslTransport.java:423)
        at org.apache.thrift.transport.TSaslTransport.read(TSaslTransport.java:405)
        at org.apache.thrift.transport.TSaslClientTransport.read(TSaslClientTransport.java:37)
        at org.apache.thrift.transport.TTransport.readAll(TTransport.java:84)
        at org.apache.thrift.protocol.TBinaryProtocol.readAll(TBinaryProtocol.java:378)
        at org.apache.thrift.protocol.TBinaryProtocol.readI32(TBinaryProtocol.java:297)
        at org.apache.thrift.protocol.TBinaryProtocol.readMessageBegin(TBinaryProtocol.java:204)
        at org.apache.thrift.TServiceClient.receiveBase(TServiceClient.java:69)
        at org.apache.hive.service.cli.thrift.TCLIService$Client.recv_FetchResults(TCLIService.java:515)
        at org.apache.hive.service.cli.thrift.TCLIService$Client.FetchResults(TCLIService.java:502)
        at com.cloudera.hive.hivecommon.api.HS2Client.fetchNRows(HS2Client.java:321)
        at com.cloudera.hive.hive.api.ExtendedHS2Client.fetchNRows(ExtendedHS2Client.java:499)
        at com.cloudera.hive.hivecommon.api.HS2Client.fetchRows(HS2Client.java:301)
        at com.cloudera.hive.hivecommon.dataengine.BackgroundFetcher.run(BackgroundFetcher.java:138)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:473)
        at java.util.concurrent.FutureTask.run(FutureTask.java:262)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
        at java.lang.Thread.run(Thread.java:748)

"Service Thread" daemon prio=10 tid=0x00007f2eb80b4800 nid=0x2562 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" daemon prio=10 tid=0x00007f2eb80b2000 nid=0x2561 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" daemon prio=10 tid=0x00007f2eb80af000 nid=0x2560 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" daemon prio=10 tid=0x00007f2eb80ad000 nid=0x255f waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" daemon prio=10 tid=0x00007f2eb807f800 nid=0x255e in Object.wait() [0x00007f2eb45f4000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000e00247f0> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:135)
        - locked <0x00000000e00247f0> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:151)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

"Reference Handler" daemon prio=10 tid=0x00007f2eb807d800 nid=0x255d in Object.wait() [0x00007f2eb46f5000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x00000000e000e1c8> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:503)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)
        - locked <0x00000000e000e1c8> (a java.lang.ref.Reference$Lock)

"main" prio=10 tid=0x00007f2eb800b800 nid=0x2557 runnable [0x00007f2ec05fb000]
   java.lang.Thread.State: RUNNABLE
        at java.lang.String.split(String.java:2289)
        at java.lang.String.split(String.java:2355)
        at com.cloudera.hive.hivecommon.dataengine.HiveJDBCQueryAnalyserUtils.queryAnalysis(HiveJDBCQueryAnalyserUtils.java:49)
        at com.cloudera.hive.hivecommon.api.HS2Buffer.getData(HS2Buffer.java:181)
        at com.cloudera.hive.hivecommon.api.HS2Client.getData(HS2Client.java:705)
        at com.cloudera.hive.hivecommon.dataengine.HiveJDBCResultSet.getData(HiveJDBCResultSet.java:265)
        at com.cloudera.hive.jdbc.common.SForwardResultSet.getData(SForwardResultSet.java:4590)
        at com.cloudera.hive.jdbc.common.SForwardResultSet.getString(SForwardResultSet.java:2138)
        at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.utils.FileUtils.writeResultSetToFile(FileUtils.java:153)
        at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.utils.DatabaseUtils.executeQueryAndWriteToFile(DatabaseUtils.java:135)
        at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.processor.JDBCProcessor.processCustomQueries(JDBCProcessor.java:84)
        at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.processor.JDBCProcessor.process(JDBCProcessor.java:47)
        at xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.main.App.main(App.java:49)

"VM Thread" prio=10 tid=0x00007f2eb8077000 nid=0x255c runnable

"GC task thread#0 (ParallelGC)" prio=10 tid=0x00007f2eb8021000 nid=0x2558 runnable

"GC task thread#1 (ParallelGC)" prio=10 tid=0x00007f2eb8023000 nid=0x2559 runnable

"GC task thread#2 (ParallelGC)" prio=10 tid=0x00007f2eb8025000 nid=0x255a runnable

"GC task thread#3 (ParallelGC)" prio=10 tid=0x00007f2eb8027000 nid=0x255b runnable

"VM Periodic Task Thread" prio=10 tid=0x00007f2eb80bf800 nid=0x2563 waiting on condition

JNI global references: 234

Heap
 PSYoungGen      total 160768K, used 126191K [0x00000000f5500000, 0x00000000ffd80000, 0x0000000100000000)
  eden space 149504K, 84% used [0x00000000f5500000,0x00000000fd033ef8,0x00000000fe700000)
  from space 11264K, 0% used [0x00000000fe700000,0x00000000fe708000,0x00000000ff200000)
  to   space 10240K, 0% used [0x00000000ff380000,0x00000000ff380000,0x00000000ffd80000)
 ParOldGen       total 349184K, used 192583K [0x00000000e0000000, 0x00000000f5500000, 0x00000000f5500000)
  object space 349184K, 55% used [0x00000000e0000000,0x00000000ebc11df8,0x00000000f5500000)
 PSPermGen       total 21504K, used 12023K [0x00000000d5a00000, 0x00000000d6f00000, 0x00000000e0000000)
  object space 21504K, 55% used [0x00000000d5a00000,0x00000000d65bde38,0x00000000d6f00000)

Answer 1

Well, not an answer, but some reminders that need space:

1) You're using an ArrayList, starting with zero capacity... it has to re-size its buffer quite often, because arraylist size grows like this: 0 -> 1 -> 2 -> 4 -> 7 -> 11 -> 17 . So instead of List<String> valueList = new ArrayList<String>(0); use List<String> headerList = new ArrayList<String>(columnCount); Instead of valueList = new ArrayList<String>(0); use valueList.clear();

2) You should use resource-try-catch, lot easier to handle.

3) The code - or rather: behind the curtains - is a lot of parsing... parsing the SQL result, then 'parsing' the data (has to be escaped in a CSV compatible way). Do not underestimate this! Even more so, if this CSVPrinter does some additional formatting, like additional spacing to keep the text file looking like a table, etc.

4) In addition, Apache libraries are not know for their speed, nor for their resource efficiency!

5) Manually flushing (as read in the comments) is not good for performance!

6) From what it looks like, your method writeResultSetToFile() is called from a loop. I do not know, but if you tell us about '3% usage' this sounds like a sustained task, ie a loop. So, SUPPOSING there is a loop, and that loop is directly responsible for the 3% CPU usage, it seems to loop some thousand times per second. If you now - on each call - retrieve and store TWO MILLION lines of text, this will slow down the whole program. CONSIDERABLY. Maybe you should not write that file so often? Maybe once a minute suffices? However often, you might think about using a decoupled thread that runs parallel to the main loop.