Friday June 27, 2008
I work from home in Chennai, India. There is maintenance power shutdown in my part of the city today [from 9.00 AM to 5.00 PM). I'm writing this blog from a Sun office in Apeejay Business Centre, Chennai. It is nice to be in an office after quite some time - at least as a change! But, I think I'd rather prefer to avoid travel, preparation to go office etc. every day 
Thursday June 26, 2008
If you have used DTrace, chances are that you have used aggregations. For performance issues, aggregated data is often more useful than individual data points. With BTrace, aggregating data is bit painful (you have to manage using Maps explicitly). It would be nice to have DTrace-style aggregation functions such as sum, max, min and so on. Glencross, Christian M (cited in my previous entry) has contributed code changes, doc and a sample for easy-to-use aggregation facility for BTrace. Please refer to the sample code (JdbcQueries.java) that demonstrates aggregations.
Now something unrelated to aggregations, but related to BTrace : I came to know about another use-case of BTrace. See also http://blog.igorminar.com/2008/06/btrace-dtrace-for-java.html
Monday June 16, 2008 In the last few weeks, I came to know about two cases of real world use of BTrace.
import static com.sun.btrace.BTraceUtils.*;
import java.sql.Statement;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;
import com.sun.btrace.*;
import com.sun.btrace.annotations.*;
/**
* BTrace script to print timings for all executed JDBC statements on an event.
* <p>
*
* @author Chris Glencross
*/
@BTrace
public class JdbcQueries {
private static Map preparedStatementDescriptions = newWeakMap();
private static Map statementDurations = newHashMap();
// VERBOSE: @TLS makes the field "thread local" -- sort of like using java.lang.ThreadLocal
@TLS
private static String preparingStatement;
@TLS
private static long timeStampNanos;
@TLS
private static String executingStatement;
/**
* If "--stack" is passed on command line, print the Java stack trace of the JDBC statement.
*
* VERBOSE: Command line arguments to BTrace are accessed as $(N) where N is the command line arg position.
*
* Otherwise we print the SQL.
*/
private static boolean useStackTrace = $(2) != null && strcmp("--stack", $(2)) == 0;
// The first couple of probes capture whenever prepared statement and callable statements are
// instantiated, in order to let us track what SQL they contain.
/**
* Capture SQL used to create prepared statements.
*
* VERBOSE: +foo in clazz means foo and it's subtypes. Note the use of regular expression
* for method names. With that BTrace matches all methods starting with "prepare". The
* type "AnyType" matches any Java type.
*
* @param args - the list of method parameters. args[1] is the SQL.
*/
@OnMethod(clazz = "+java.sql.Connection", method = "/prepare.*/")
public static void onPrepare(AnyType[] args) {
preparingStatement = useStackTrace ? jstackStr() : str(args[1]);
}
/**
* Cache SQL associated with a prepared statement.
*
* VERBOSE: By default, @OnMethod matches method entry points. Modifying with @Location
* annotation to match the method return points.
*
* @param arg - the return value from the prepareXxx() method.
*/
@OnMethod(clazz = "+java.sql.Connection", method = "/prepare.*/", location = @Location(Kind.RETURN))
public static void onPrepareReturn(AnyType arg) {
if (preparingStatement != null) {
print("P"); // Debug Prepared
Statement preparedStatement = (Statement) arg;
put(preparedStatementDescriptions, preparedStatement, preparingStatement);
preparingStatement = null;
}
}
// The next couple of probes intercept the execution of a statement. If it execute with no-args,
// then it must be a prepared statement or callable statement. Get the SQL from the probes up above.
// Otherwise the SQL is in the first argument.
@OnMethod(clazz = "+java.sql.Statement", method = "/execute.*/")
public static void onExecute(AnyType[] args) {
timeStampNanos = timeNanos();
if (args.length == 1) {
// No SQL argument; lookup the SQL from the prepared statement
Statement currentStatement = (Statement) args[0]; // this
executingStatement = get(preparedStatementDescriptions, currentStatement);
} else {
// Direct SQL in the first argument
executingStatement = useStackTrace ? jstackStr() : str(args[1]);
}
}
@OnMethod(clazz = "+java.sql.Statement", method = "/execute.*/", location = @Location(Kind.RETURN))
public static void onExecuteReturn() {
if (executingStatement == null) {
return;
}
print("X"); // Debug Executed
long durationMicros = (timeNanos() - timeStampNanos) / 1000;
AtomicLong ai = get(statementDurations, executingStatement);
if (ai == null) {
ai = newAtomicLong(durationMicros);
put(statementDurations, executingStatement, ai);
} else {
addAndGet(ai, durationMicros);
}
executingStatement = null;
}
// VERBOSE: @OnEvent probe fires whenever BTrace client sends "event" command.
// The command line BTrace client sends BTrace events when user pressed Ctrl-C
// (more precisely, on receiving SIGINT signal)
@OnEvent
public static void onEvent() {
println("---------------------------------------------");
printNumberMap("JDBC statement executions / microseconds:", statementDurations);
println("---------------------------------------------");
}
}
And he has expressed few wish lists for BTrace based on his experience with DTrace. We plan to investigate those items in near future.