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An (incomplete) interface to the Bitcask storage system

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README.markdown

Bitcask

Utilities for reading the Bitcask file format. You can use this to recover deleted values (before they are compacted), recover from a backup, list keys to do read-repair when list-keys is malfunctioning, and so forth.

Install

$ gem install bitcask

Examples

Open a bitcask.

b = Bitcask.new '/var/lib/riak/bitcask/0'

Load the keydir, using hintfiles where possible.

b.load

Get a specific entry:

b['test'] #=> 'value_of_test'

Iterate over all values:

b.each do |key, value|
  puts key
  puts value
end

In Riak, these are erlang terms.

b.each do |key, value|
  next if value == Bitcask::TOMBSTONE

  bucket, key = BERT.decode key
  value = BERT.decode value

  # Store the object's value in riak
  o = riak[bucket][key]
  o.raw_data = value.last
  o.store

  # Or dump the entire value to a file for later inspection.
  FileUtils.mkdir_p(bucket)
  File.open(File.join(bucket, key), 'w') do |out|
    out.write value.to_json
  end
end

You can also work directly on the data files. Here's how to dump all keys and values, in cron order, excluding tombstones. Data files go in cronological order, so this is in effect replaying history since the last merge.

b.data_files.each do |data_file|
  data_file.each do |entry|
    next if entry.value == Bitcask::TOMBSTONE
    puts entry.key
    puts entry.value
  end
end

If you know the offset, you can retrieve it directly from a DataFile.

data_file[0] # => Struct {:key => 'key', :value => 'value'}

And step through values one by one.

data_file.read # => [k1, v1]
data_file.read # => [k2, v2]

Seek, rewind, and pos are also supported.

You'd be surprised how fast this is. 10,000 values/sec, easy.

Utility

bin/bitcask is a small tool to inspect bitcask files. It's designed for integration with Riak (parsing keys as erlang {bucket, key} tuples, for instance), but can be content agnostic as well. It uses various tricks to do things quickly, like only scanning hintfiles when values aren't involved.

Show all comments.

bitcask /var/lib/riak --bucket comments --color all

Get the keys of the last 10 users written to bitcask

bitcask /var/lib/riak --bucket users --color -f '%k' last --limit 10

Show the full structure of a given user. Here the two arguments after get are presumed to be --bucket and --key.

bitcask /var/lib/riak --verbose-values get users sauron

Show all the changes to a given key and value over time.

bitcask /var/lib/riak --bucket users --key sauron --format '%v' dump

Count a bucket in a specific bitcask.

bitcask /var/lib/riak/bitcask/0 --bucket magic_rings count

Status

Anyone who wants to expand this, feel free. I've been using it for emergency recovery operations, but don't plan to reimplement bitcask in Ruby myself. I welcome pull requests.

License

This software was written by Kyle Kingsbury aphyr@aphyr.com, at Remixation, Inc., for their iPad social video app "Showyou". Released under the MIT license.

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