Print stacktraces for all threads on shutdown

If your microservice stops responding from time to time, and they only way out is to kill it with SIGINT or SIGTERM then adding a shutdown hook might be the way to go. Do note that this will not work if you kill the process with SIGKILL (-9), cause that will result in an unclean shutdown.

Some of this code is heavily influenced by Print all of the thread’s information and stack traces : Exception « Development « Java Tutorial. But has been translated into Scala, and cleaned up a little.

The output would look something like this

 

UDF/User Defined Functions in Cassandra 3.x

I was just playing around with Cassandra WRITETIME and thought it was somewhat difficult to figure out the date / timestamp of a number like this (microseconds since EPOC) 1470645914253000.

So in my example it looked like this

So I figured why not create a UDF that would solve this for me

That turned out to be a little bit of a challenge …

I thought that I could do like this

BUT NO, YOU CAN NOT!!!

There are several WRONGS in here it turns out

  1. First off you have to turn on
    enable_user_defined_functions: true
    in the conf/cassandra.yaml file
  2. All classes has to be fully qualified, so Date would be java.util.Date, and so on…
  3. The division operator ‘/’ can not be used !!! however +,- and * works fine. surely this must be a bug … this called for some thinking…

The error I got when trying to use the code above without fully qualified names was

And the reason, if I got it right, is that you can not do imports.

The error I got when trying to use the division ‘/’ operator was this:

The code that works looks like this, using java.math.BigDecimal to solve it was perhaps a so-so solution, but it works:

So now my output in cqlsh.sh looks like this now

That is a lot better !

Cassandra set the writetime explicitly with a PreparedStatement

This is a quick one, I wanted to set the writetime of a row explicitly when I populate the database for testing purposes. We use the writetime of a column to filter them out.

It required some looking around to find out how to do this…. so I figured I write an article about it.

The timestamp will be set for ALL cells in this row (well not the primary key, cause it does not have a timestamp, but the others).

The timestamp is given as milliseconds since EPOC, so lots of digits :-).

A prepared statement would then look like this (Scala code)

TTL and TIMESTAMP can both be set like this, i.e. with [ttl] and [timestamp]

-Tobias

DTrace;ing the JVM, useful tips

I am using DTrace from time to time and it is really nice, you can do a lot with it.

This page is mostly a reminder to myself cause there are tons of pages out there if you google it, but I figured that why not share the knowledge 🙂

List all Probes available in a process

 List all probes that has to do with the JAVA JVM Hotspot

dtrace -l | grep hotspot

Figure out WHO initiated the Garbage Collection (GC)

dtrace -n ‘hotspot$target:::gc-begin { jstack(); }’ -p 25736

JVM Probes

http://docs.oracle.com/javase/6/docs/technotes/guides/vm/dtrace.html

Figure out what objects are being allocated using DTrace

http://prefetch.net/blog/index.php/2007/10/31/using-the-dtrace-hotspot-provider-to-observe-java-object-allocations/

JVM: Unable to open door

The jinfo command needs to be run by the user the JVM runs as.