Skip to main content

Zookeeper watchers and events, a (very) short summary

Here is a summary of what events are expected if you set ChildrenWatcher, DataWatcher or ExistsWatcher on a znode :

WARNING : none means that no event is triggered, do no confuse with EventType.None

Do not forget this basic rule : Watches are one time trigger, once a watch has been triggered you must register it once again if you want to be notified. Moreover due to network latency you can miss one or several changes that happen just before the watch is re-registered.

An expired zookeeper session also means that all your watches are gone, you have to create them once again.

More informations here.

Hope it helps...
Labels:

Comments

Post a Comment

Popular posts from this blog

Orientée colonnes ?

Les bases NoSQL sont arrivées avec leur cortège de nouveautés et pour certaines d'entre elles une notion héritée de BigTable : celle de base de donnée orientée colonne. Cependant faire le lien entre l'article de Wikipedia et comprendre ce que permet réellement un base de donnée comme HBase n'est pas une chose évidente. En effet le simple fait de définir cette notion ne suffit pas toujours a bien comprendre quels sont les principes de conception du monde SQL qui peuvent être oubliés et ceux qui doivent être appris. Colonne or not colonne ? Prenons un modèle très simple de donnée et essayons de le transposer dans un modèle "orienté colonne": Comme on peut le voir on est passé d'un modèle à 2 dimensions (ligne x colonne) vers un modèle où une valeur est accédée au travers de 2  coordonnées qui sont ici (ligne, colonne) Cette notion de coordonnées est  importante  (c'est pour ça que je la met en gras 2 fois de suite) si l'on veut c
Post a Comment
Read more

Row Count : HBase Aggregation example

With the coprocessors HBase 0.92 introduces a new way to process data directly on a region server. As a user this is definitively a very exciting feature : now you can easily define your own distributed data services. This post is not intended to help you how to define them (i highly recommend you to watch this presentation if you want to do so) but to quickly presents the new aggregation service shipped with HBase 0.92 that is built upon the endpoint coprocessor framework. 1. Enable AggregationClient coprocessor You have two choices : You can enable aggregation coprocessor on all your tables by adding the following lines to hbase-site.xml : <property> <name>hbase.coprocessor.user.region.classes</name> <value>org.apache.hadoop.hbase.coprocessor.AggregateImplementation</value> </property> or ...you can enable coprocessor only on a table throught the HBase shell : 1. disable the table hbase> disable ' mytable ' 2.
Post a Comment
Read more

HBase + Subversion + Eclipse + Windows

HBase + Subversion + Eclipse + Windows (it should be easy to adapt for Linux) Update : please note that since HBase-4336 / HBase 0.96 the source tree is split in more than one Maven module this post is no more relevant, i have created a new post on this subject : http://michaelmorello.blogspot.fr/2012/06/hbase-096-eclipse-maven.html This is a simple setup in order to play with the source code of HBase under Microsoft Windows. Since HBase use some Unix specific commands like chmod the only requirements here are  Cygwin and a working Maven 3 environment. (It is obvious that you need Java and Eclipse , but you DON'T need anything else like the Eclipse Maven plugin or any SSH configuration) 1. Checkout the source code The first step is to check out the source code from the Subversion repository. I did it under my cygwin home repository. In this example i want to play with the 0.90 branch : svn co http://svn.apache.org/repos/asf/hbase/branches/0.90/ hbase-0.90
6 comments
Read more