add README.md back in for apps

3 files changed, 79 insertions, 0 deletions

diff --git a/apps/fabric/README.md b/apps/fabric/README.md
new file mode 100644
index 00000000..2d7f1ae2
--- /dev/null
+++ b/apps/fabric/README.md
@@ -0,0 +1,27 @@
+## fabric
+
+Fabric is a collection of proxy functions for [CouchDB][1] operations in a cluster.  These functions are used in [BigCouch][2] as the remote procedure endpoints on each of the cluster nodes.
+
+For example, creating a database is a straightforward task in standalone CouchDB, but for BigCouch, each node that will store a shard/partition for the database needs to receive and execute a fabric function.  The node handling the request also needs to compile the results from each of the nodes and respond accordingly to the client.
+
+Fabric is used in conjunction with 'Rexi' which is also an application within BigCouch.
+
+### Getting Started
+Dependencies:
+ * Erlang R13B-03 (or higher)
+
+Build with rebar:
+    make
+
+### License
+[Apache 2.0][3]
+
+### Contact
+ * [http://cloudant.com][4]
+ * [info@cloudant.com][5]
+
+[1]: http://couchdb.apache.org
+[2]: http://github.com/cloudant/bigcouch
+[3]: http://www.apache.org/licenses/LICENSE-2.0.html
+[4]: http://cloudant.com
+[5]: mailto:info@cloudant.com
diff --git a/apps/mem3/README.md b/apps/mem3/README.md
new file mode 100644
index 00000000..4fa75906
--- /dev/null
+++ b/apps/mem3/README.md
@@ -0,0 +1,25 @@
+## mem3
+
+Mem3 is the node membership application for clustered [CouchDB][1].  It is used in [BigCouch][2] and tracks two very important things for the cluster:
+
+ 1. member nodes
+ 2. node/partition mappings for each database
+
+Both the nodes and partitions are tracked in node-local couch databases.  Partitions are heavily used, so an ETS cache is also maintained for low-latency lookups.  The nodes and partitions are synchronized via continuous CouchDB replication, which serves as 'gossip' in Dynamo parlance.  The partitions ETS cache is kept in sync based on membership and database event listeners.
+
+A very important point to make here is that BigCouch does not necessarily divide up each database into equal partitions across the nodes of a cluster.  For instance, in a 20-node cluster, you may have the need to create a small database with very few documents.  For efficiency reasons, you may create your database with Q=4 and keep the default of N=3.  This means you only have 12 partitions total, so 8 nodes will hold none of the data for this database.  Given this feature, we even partition use out across the cluster by altering the 'start' node for the database's partitions.
+
+Splitting and merging partitions is an immature feature of the system, and will require attention in the near-term.  We believe we can implement both functions and perform them while the database remains online.
+
+### License
+[Apache 2.0][3]
+
+### Contact
+ * [http://cloudant.com][4]
+ * [info@cloudant.com][5]
+
+[1]: http://couchdb.apache.org
+[2]: http://github.com/cloudant/bigcouch
+[3]: http://www.apache.org/licenses/LICENSE-2.0.html
+[4]: http://cloudant.com
+[5]: mailto:info@cloudant.com
diff --git a/apps/rexi/README.md b/apps/rexi/README.md
new file mode 100644
index 00000000..995916a6
--- /dev/null
+++ b/apps/rexi/README.md
@@ -0,0 +1,27 @@
+## rexi
+
+Rexi is a tailor-made RPC server application for sending [CouchDB][1] operations to nodes in a cluster.  It is used in [BigCouch][2] as the remote procedure vehicle to get 'fabric' functions to execute on remote cluster nodes.
+
+Rexi better fits the needs of the BigCouch distributed data store by dropping some unneeded overhead in rex, the RPC server that ships with Erlang/OTP.  Rexi is optimized for the case when you need to spawn a bunch of remote processes.  Cast messages are sent from the origin to the remote rexi server, and local processes are spawned from there, which is vastly more efficient than spawning remote processes from the origin.  You still get monitoring of the remote processes, but the request-handling process doesn't get stuck trying to connect to an overloaded/dead node.  'rexi_DOWN' messages will arrive at the client eventually.  This has been an extremely advantageous mix of latency and failure detection, vastly improving the performance of BigCouch.
+
+Rexi is used in conjunction with 'Fabric' which is also an application within BigCouch, but can be used on a stand-alone basis.
+
+### Getting Started
+Dependencies:
+ * Erlang R13B-03 (or higher)
+
+Build with rebar:
+    make
+
+### License
+[Apache 2.0][3]
+
+### Contact
+ * [http://cloudant.com][4]
+ * [info@cloudant.com][5]
+
+[1]: http://couchdb.apache.org
+[2]: http://github.com/cloudant/BigCouch
+[3]: http://www.apache.org/licenses/LICENSE-2.0.html
+[4]: http://cloudant.com
+[5]: mailto:info@cloudant.com