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 ("127.0.0.1", 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
  insert
      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-2.1.0.1 ... linking ... done.

Loading package network-2.2.1.5 ... linking ... done.

Loading package Thrift-0.1.0 ... linking ... done.

Loading package array-0.3.0.0 ... linking ... done.

Loading package containers-0.3.0.0 ... linking ... done.

Loading package old-locale-1.0.0.2 ... linking ... done.

Loading package old-time-1.0.0.3 ... 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..

cheers,

-kirk