author: urjit singh bhatia
url: about.me/urjitbhatia
email: [email protected]

####SpyderCache is a distributed cache written in python.####

#####There are 3 main parts:#####

1. Topology Layer
   This layer is responsible for knowing where its peers are and talking to them over a 'peer-channel'. A sub-system of this layer is the KeyManager which is an implementation of consistent hashing (Thanks http://amix.dk/blog/post/19367 for the boiler-plate code).

2. Communication Layer
   This layer is responsible for gathering requests from clients and using appropriate layers in the system to accomplish the requested tasks. This layer runs cocooned in a thin web-server - currently CherryPy based on some benchmarks here: http://nichol.as/benchmark-of-python-web-servers.

3. Caching Layer
   This layer is responsible for storing the data in memory. Support for recovery from disk is available, which will allow a dead node to recover its last known state.

Installing dependencies:

Python Version:
This was built using python 2.7.2. on Ubuntu 11.10 [GCC 4.6.1]

Use a package manager like pip and install the following packages:
1. python-msgpack
2. cherrypy

Features available currently:

1. Simple file based configuration of the system. Explanation of a complete config file follows.
2. If a node goes down on the fly, other nodes assume responsibility for the data. Bringing a node back to life is very easy. It starts caching its share of data as soon as it can.

Example: This is the configuration file.

[local]
node_id = 1				
#this is the id of the node which this file will drive. Any string is valid    

node_port = 8001			
#the port at which this node should communicate. valid entry regex \:[0-9]{4,5}$    

reconstruct = False			
#should the node read the events journal to restore last known state? valid: True/False    

cache_size = 1000			
#Maximum number of keys this cache is allowed to hold. After this limit is hit,    
#the cache will start evicting keys using an LRU mechanism    

[network]					
#simply the list of peers this node should connect to.    

peer = 127.0.0.1:8002,		
		127.0.0.1:8003		
#it is a comma separated list of the form <ipv4address>:<port>    
#valid entry regex is: ^([0-9]{1,3}\.){3}[0-9]{1,3}\:[0-9]{4,5}$    

This file will fire node 8001 and instruct it to connect to nodes 8002 and 8003 as its distribution partners.    

TODO:

[DONE] Add support for journaling to disk so that we can reinstate a node to its last known state.
Add cache invalidation message from peer nodes.
[DONE] Add heartbeat monitoring and thin master to maintain the system.

#####Command scripts:#####

See utils directory for some standalone command scripts.
Example:

use put.py to put a key value pair onto a node
python put.py key value 127.0.0.1 8001

This will put the key 'key' and its value 'value' on the appropriate node.

Scripts:

connect.py - Connect to a given node on the fly
get.py - Get a key
put.py - Put a key-value data item
delete.py - Delete a key
fake_death.py - Kill a node	
reconstruct.py - Reconstruct a node from its data log