A NoClassDefFoundError always means classpath (or classloader, but
that's unlikely here unless you're on Storm 1.0.0 and less) issues. Take
a look at which class it cannot find and find out why it's not in the
jar you're sending to Storm.
A ExceptionInitializerError tells us nothing without its cause. Some
initializer failed, go take a look which one and why.
Long story short - there's noting special about Storm and singletons. As
always, all the instantiated classes in your topology (things that get
pushed into the TopologyBuilder) must be correctly serializable and
deserializable (did you forget to handle a transient field somewhere?).
Otherwise, without a minima example of the problem I'm afraid there
isn't much we can do for you.
PJ
Dne 15.07.2019 v 15:33 Denis Sevosteenko napsal(a):
Just to clarify: I know this can possibly happen because of
incorrectly packaged jar, but there are no such issues when we aren't
using singletons. Nothing like this happens when I just add a new bolt
with a new mongodb connection for example.
Also regarding abstracting DB connection logic to a separate bolt: we
are using a bolt to write data to Cassandra, but I have no idea how to
do that with reads.
On Mon, Jul 15, 2019 at 4:16 PM Denis Sevosteenko
<denis.sevostee...@gmail.com <mailto:denis.sevostee...@gmail.com>> wrote:
We got NoClassDefFoundError and ExceptionInitializerError in
prepare() methods.
On Mon, Jul 15, 2019 at 4:13 PM Petr Janeček
<janecekp...@seznam.cz <mailto:janecekp...@seznam.cz>> wrote:
Hello,
you'll need to define "fallen apart". What did not work and
why? Obviously a singleton is single in one Worker (one JVM).
For DB connections, this seems to be a good thing - you'll
want every JVM to have a single (or, rather, a limited pool
of) DB connection encapsulated in a singleton resource.
If you want a singleton to really be single in the topology,
you'll need to abstract away the DB connection logic to a
separate microservice, or a single bolt.
PJ
---------- Původní e-mail ----------
Od: Denis Sevosteenko <denis.sevostee...@gmail.com
<mailto:denis.sevostee...@gmail.com>>
Komu: user@storm.apache.org <mailto:user@storm.apache.org>
Datum: 15. 7. 2019 15:08:26
Předmět: Storm and singletons
Hi all,
This may be an old question, but what is the correct way
of using Singleton pattern with Storm?
Currently we have a topology with around 200 bolts, of
which around 50 read and write data from/to Cassandra.
Each of these 50 bolts creates a new Cassandra session,
which to my understanding of Cassandra is not great. We
have tried solving this issue with several implementations
of singletons: lazy static, eager static and enum. All of
these implementations have worked in dev environment
running on single server, but have fallen apart on QA
environment which has two supervisor hosts. I'm new to
Storm so I have no idea if we are missing something
crucial or obvious.
Thanks & Regards,
Denis Sevosteenko
