The last time our team worked on Esper for complex event processing, it was version 3.4.0. One of the requirement we envisaged was for EPL statements to be externalized into configuration files rather than keeping them in code. So, we came up with this XML configuration file where one can configure EPLs, provide certain attributes (epl-name, enable/disable etc.) and associate them with a listener.

Working on Esper (v4.9.0) again and I met "EPL Modules", a very useful feature which renders our earlier custom-xml-configurations for epl almost useless. Though this feature was introduced long back in v3.5.0 itself, it is recently that came to know about it.

More than a year back, during some research related to CEP, I came across Storm which was "touted" as being a CEP engine and it was very difficult to come to terms with these assertions. Storm and S4 had just entered the market; for me, having some prior experience with ESPER, there was no comparision between ESPER and Storm/S4.

Reviewing Storm a year later now (Release 0.8.2) and it seems very mature, popular as well as very equipped to be used as a CEP engine.

Since the day one when we started working on Storm, I was mistaken on spouts modus operandi. I believed spouts can both pull and push data from the sources. But when I was about to implement a push styled spout, I stumbled with a few challenges.

I wanted to build a thrift base spout such that different event sources can push data on it. I found one such implementation storm-scribe (https://github.com/stormprocessor/storm-scribe) and on its wiki it quotes this to be a push styled.

Yesterday our Cassandra development cluster broke down, Mahendra reported that on executing any statement on cassandra-cli, it errs prompting a weird message 'schema disagreement error' on console. I googled, my usual way of being :) and found this FAQ on Cassandra wiki. This clearly describes the problem's reason:

Prior to Cassandra 1.1 and 1.2, Cassandra schema updates assume that schema changes are done one-at-a-time.
Loading