Question

The following code is throwing OutofMemoryError on Linux 3.5 enterprise box running jdk1.6.0_14 but running fine on JDK 1.6.0_20 I am clueless why its happening.

while (rs.next()) {
  for (TableMetaData tabMeta : metaList) {
rec.append(getFormattedString(rs, tabMeta));
  }
  rec.append(lf);
  recCount++;
  if (recCount % maxRecBeforWrite == 0) {
    bOutStream.write(rec.toString().getBytes());
    rec = null;
    rec = new StringBuilder();
  }
}
bOutStream.write(rec.toString().getBytes());

The getFormattedString() method goes here:

private String getFormattedString(ResultSet rs, TableMetaData tabMeta)
        throws SQLException, IOException {

    String colValue = null;
    // check if it is a CLOB column
    if (tabMeta.isCLOB()) {
        // Column is a CLOB, so fetch it and retrieve first clobLimit chars.
        colValue = String.format("%-" + clobLimit + "s", getCLOBString(rs,
                tabMeta));
    } else {
        colValue = String.format("%-" + tabMeta.getColumnSize() + "s", rs
                .getString(tabMeta.getColumnName()));
    }
    return colValue;
}

Below is the exception trace:

Exception in thread "main" java.lang.OutOfMemoryError: GC overhead limit exceeded
        at java.util.Formatter$FormatSpecifier.justify(Formatter.java:2827)
        at java.util.Formatter$FormatSpecifier.print(Formatter.java:2821)
        at java.util.Formatter$FormatSpecifier.printString(Formatter.java:2794)
        at java.util.Formatter$FormatSpecifier.print(Formatter.java:2677)
        at java.util.Formatter.format(Formatter.java:2433)
        at java.util.Formatter.format(Formatter.java:2367)
        at java.lang.String.format(String.java:2769)
        at com.boa.cpal.cpal2repnet.main.CPALToReportNet.getFormattedString(Unknown Source)

I suspect that the use of String.format is the culprit, but not sure. How to overcome this issue?

Please note that this code has been written to query on the database that have huge tables to read the resultset and create extract files with specific formatting.

Answer 1

The exception you are getting refers to the GC overhead limit that is enabled by this HotSpot option:

-XX:+UseGCOverheadLimit -Use a policy that limits the proportion of the VM’s time that is spent in GC before an OutOfMemory error is thrown. (Introduced in 6.)

So, my best guess is that your application is simply running out of heap space. As @Andreas_D’s answer says, the default heap sizes were changed between jdk1.6.0_14 and JDK 1.6.0_20, and that could explain the different behaviour. Your options are:

• Upgrade to the later JVM. (UPDATE – 2012/06 even JDK 1.6.0_20 is now very out of date. Later 1.6 and 1.7 releases have numerous security fixes.)

• Explicitly set the heap dimensions -Xmx and -Xms options when launching the JVM. If you are already doing this (on the older JVM), increase the numbers so that the maximum heap size is larger.

You could also adjust the GC overhead limit, but that’s probably a bad idea on a production server.

If this particular problem only happens after your server has been running for some time, then maybe you’ve got memory leaks.