Saturday, March 13, 2010

Haskell & Cassandra: First Steps

Ok, so I had a few hours to finally sit down and try getting a 'Hello World' example put together for interacting with a Cassandra database from Haskell.
I used the following:
Mac OS 10.6.2
GHC 6.12.1
apache-cassandra-0.5.1 (JDK 1.6 from Apple)
thrift-incubating-0.2.0 (Compiled using GCC 4.2.1 and Boost 1.41 from MacPorts)

I uses a stock Cassandra install, and did not customize the included example schema, starting the server with
$ cd apache-cassandra-0.5.1
$ bin/cassandra -f

Getting the thrift compiler built and the Thrift lib installed into GHC proved to be a pain point for me, and will be the topic of a subsequent post if others have a similar experience.

Once the Thrift package is installed in GHC, and you have used the thrift compiler to compile compile the Cassandra interface definition file
$ thrift --gen hs apache-cassandra-0.5.1/interface.cassandra.thrift

You should have the generated Haskell cassandra sources:
-rw-r--r-- 1 kirk kirk 83431 Mar 13 09:57 Cassandra.hs
-rw-r--r-- 1 kirk kirk 16946 Mar 13 09:57 Cassandra_Client.hs
-rw-r--r-- 1 kirk kirk 613 Mar 13 09:57 Cassandra_Consts.hs
-rw-r--r-- 1 kirk kirk 1823 Mar 11 13:02 Cassandra_Iface.hs
-rw-r--r-- 1 kirk kirk 19015 Mar 13 09:56 Cassandra_Types.hs

Unfortunately, there is little API docs to go on here for haskellers, but I was able to finally duplicate the Java example from the Cassandra Wiki using a default Cassandra install and schema:

{-# LANGUAGE DeriveDataTypeable #-}

import Network
import System.IO
import Thrift.Protocol.Binary
import Thrift.Transport.Handle
import Cassandra_Client
import Cassandra_Types

import System.Time

main = do
-- connect to Cassandra running locally
handle <- hOpen ("", PortNumber 9160)

TOD sec usec <- getClockTime -- were using old-time here, but really we jsut need a good
-- Int64 value for the timestamp

let binpro = BinaryProtocol handle
let proto = (binpro, binpro) -- no idea why the Casandra API splits into (in an out proto, but w/e)

-- put some data into the column
proto -- The protocol/transport value
"Keyspace1" -- the KeySpace (typically this will be your app's name)
"kirk" -- The "row" id, or in cassandra-speak, the key
(ColumnPath -- Column paths point to either a colum or a super column
(Just "Standard1") -- The column family
Nothing -- The super column name
(Just "name")) -- The column name
"Kirk Peterson" -- The value to insert into the column
(fromInteger sec) -- The timestamp for the insert
ONE -- The ConsistencyLevel to enforce on the insert

-- pull the value back out
r <- get_slice
proto -- more protocol/tranport stuff
"Keyspace1" -- the KeySpace (typically this will be your app's name)
"kirk" -- again, the key
(ColumnParent -- similar to column path, the column parent.
(Just "Standard1") -- the Column Family
Nothing) -- the super column (not used in our example)
(SlicePredicate -- predicate/filter for row, either by column names and/or by a slice range
Nothing -- Column Names to filter on (not used in ut example)
(Just (SliceRange -- A SliceRange
(Just "") -- Range Start
(Just "") -- Range End
(Just False) -- Results Reversed?
(Just 10)))) -- Result Count
ONE -- The ConsistencyLevel to enforce on the read

putStrLn $ "found " ++ (show $ length r) ++ " record(s)"
mapM_ (putStrLn . show) r

hClose handle

When compiled (or ran from ghci) you should see something similar to the following:
*Main> main
Loading package parsec- ... linking ... done.
Loading package network- ... linking ... done.
Loading package Thrift-0.1.0 ... linking ... done.
Loading package array- ... linking ... done.
Loading package containers- ... linking ... done.
Loading package old-locale- ... linking ... done.
Loading package old-time- ... linking ... done.
found 1 record(s)
ColumnOrSuperColumn {f_ColumnOrSuperColumn_column = Just (Column {f_Column_name = Just "name", f_Column_value = Just "Kirk Peterson", f_Column_timestamp = Just 1268515834}), f_ColumnOrSuperColumn_super_column = Nothing}

Win! Cassandra wrote a record to the datastore, and was able to read it back.
Hopefully this help you get your cassandra app up and running, thats all I have for now, hit me with your questions/ experiences in the comments, and hopefully I can help..


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  • thanks a lot for this post. this is an area i would also like to explore. please post anything interesting you find, and if you can, post it to the haskell category at, or perhaps the haskell-cafe list. i'm sure others are also interested

    By Blogger brad, at 9:56 PM  

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