ganapati – Hadoop HDFS Thrift interface for Ruby¶ ↑

Ganapati is a Ruby thrift lib for interfacing with Hadoop’s distributed file system, HDFS. It also includes a few command line client utilities.

To install:

gem install ganapati

Documentation in Hadoop for the thrift interface to HDFS is crap. It can be found here.

As a much simpler and safer way of auto compiling and then starting the thrift interface, use the provided script:

bin/hdfs_thrift_server <port>

This will start a thrift server on the given port (after compiling the server code provided in the Hadoop distribution).

require 'rubygems'
require 'ganapati'

# args are host, port, and optional timeout
client = Ganapati::Client.new 'localhost', 1234

# copy a file to hdfs
client.put("/some/file", "/some/hadoop/path")

# get a file from hadoop
client.get("/some/hadoop/path", "/local/path")

# Create a file
f = client.create("/home/someuser/afile.txt")
f.write("this is some text")
# Always, always close the file
f.close 

# Create a file with code block
client.create("/home/someuser/afile.txt") { |f|
  f.write("this is some text")
}

# Open a file for reading and read it
client.open('/home/someuser/afile.txt') { |f| 
  puts f.read 
  # or read for specific length from start
  puts f.read(0, 4)
}

# read a file line by line
client.readlines('/home/someuser/afile.txt') { |line|
  puts line
}

# Open a file for appending and append to it
client.append('/home/someuser/afile.txt') { |f| 
  f.write "new data" 
}	  

## Common file methods are available (chown, chmod, mkdir, stat, etc).  Examples:
# move a file
client.mv "/home/someuser/afile.txt", "/home/someuser/test.txt"

# remove a file
client.rm "/home/someuser/test.txt"

# test for file existance
client.exists? "/home/someuser/test.txt"

# get a list of all files
client.ls "/home"

client.close

# Quick and dirty way to print remote file.  The run class method takes care of closing the client.
puts Ganapati::Client.run('localhost', 1234) { |c| c.open('/home/someuser/afile.txt') { |f| f.read } }

There are a few utility programs included in the bin directory. hls provides a way to see the contents of HDFS (recursively and verbosely with appropriate command line options):

./bin/hls hdfs://host:port/tmp

hcp provides a way to copy to/from/between HDFS servers:

./bin/hcp hdfs://host:port/some/path/to/file ./file
./bin/hcp ./file hdfs://host:port/some/path/to/file
./bin/hcp hdfs://anotherhost:port/some/path/to/file hdfs://host:port/some/path/to/file