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From iv...@apache.org
Subject svn commit: r1630898 - /zookeeper/bookkeeper/site/content/index.textile
Date Fri, 10 Oct 2014 14:03:05 GMT
Author: ivank
Date: Fri Oct 10 14:03:04 2014
New Revision: 1630898

URL: http://svn.apache.org/r1630898
Log:
new frontpage text for bookkeeper

Modified:
    zookeeper/bookkeeper/site/content/index.textile

Modified: zookeeper/bookkeeper/site/content/index.textile
URL: http://svn.apache.org/viewvc/zookeeper/bookkeeper/site/content/index.textile?rev=1630898&r1=1630897&r2=1630898&view=diff
==============================================================================
--- zookeeper/bookkeeper/site/content/index.textile (original)
+++ zookeeper/bookkeeper/site/content/index.textile Fri Oct 10 14:03:04 2014
@@ -20,7 +20,48 @@ h1. Welcome to Apache BookKeeper™
 
 The Apache BookKeeper subproject of ZooKeeper is made up of a distributed logging service
called BookKeeper and a distributed publish/subscribe system built on top of BookKeeper called
Hedwig.
 
-h2. What is BookKeeper?
+h2. What is Bookkeeper?
+
+Bookkeeper is a replicated log service which can be used to build
+[http://en.wikipedia.org/wiki/State_machine_replication replicated state machines]. A log
contains a sequence of events which can
+be applied to a [http://en.wikipedia.org/wiki/Finite-state_machine state machine]. Bookkeeper
guarantees that each replica
+state machine will see all the same entries, in the same order.
+
+h2. Eh? What good is that to me?
+
+Imagine for example that you have a database that you want to be able
+access even if the database server goes down. You'll need to replicate
+it to multiple servers. You need to ensure that if one database sees an
+update, all databases see the update. But what happens if one database
+server is cut off from the network for a time? Or if two clients try to
+update the same field at exactly the same instance? This is where a
+replicated log comes in.
+
+A database can be seen as a state machine. It is the sum of all the
+updates which is has applied since its initial state. Therefore, if you
+consider your replicated database as a replicated statemachine, you can
+do the replication using a replicated log service. If all updates are
+written to the log replication service before being applied to the
+database, then the database will continue to be available and consistent
+even if some of the replicas fail.
+
+This approach can be applied to many types of distributed systems, such
+as messaging systems, coordination systems, filesystems, etc.
+
+h2. What bookkeeper is not?
+
+Bookkeeper has nothing to do with application/error/trace logging. There
+are already many projects (link to log4j, slf4j, logback) dedicated to
+that problem.
+
+Bookkeeper does not provide leader election. You'll need to use something like [http://zookeeper.apache.org
Zookeeper] for that.
+
+h2. How about Hedwig?
+
+Hedwig is a distributed publish and subscribe system, which uses
+bookkeeper to replicate its messages.
+
+h2. More information
 
 Learn more about BookKeeper on the "BookKeeper Wiki":https://cwiki.apache.org/confluence/display/BOOKKEEPER/BookKeeper.
 Learn more about Hedwig on the "Hedwig Wiki":https://cwiki.apache.org/confluence/display/BOOKKEEPER/HedWig.



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