The following errata will be fixed in the second printing of the book.

• Page xvii, Acknowledgments, third paragraph

  "Kristina Chowdorow" should be "Kristina Chodorow". My apologies to Kristina!

• Page 11, Transaction logging sidebar

  "random I/O is much slower that sequential I/O" should read "random I/O is much slower than sequential I/O"

• Page 16, Final sentence under "Command-line tools"

  monfile should read mongofiles

• Page 21, Final paragraph before 1.5, last sentence

  "may greatly simply" should read "may greatly simplify"

• Page 21, Footnote 12

  The <code> tags should not be visible.

• Page 39, Code snippet before 3.1.2

  $ruby connect.rb

  should read

  $ ruby connect.rb

• Page 39, Code snippet at the bottom of the page

  $ irb -r connect.rb

  should read

  $ irb -r ./connect.rb

• Page 45, The title in Figure 3.2

  "_id" => ObjectId('4c2a...')

  should read

  "_id" => BSON::ObjectId('4c2a...')

• Page 45, Figure 3.2

  The document length should be little-endian (38 0 0 0). Each fields last byte should be understood as a null terminator: '\0'.

• Page 48, Code snippet

  def save_tweets_for(term)
    Twitter::Search.new.containing(term).each do |tweet|
      @tweets_found  += 1
      tweet_with_tag = tweet.to_hash.merge!({"tags" => [term]})
      @tweets.save(tweet_with_tag)
    end
  end

  should read

  def save_tweets_for(term)
    Twitter.search(term).each do |tweet|
      @tweets_found  += 1
      tweet_with_tag = tweet.to_hash.merge!({"tags" => [term]})
      @tweets.save(tweet_with_tag)
    end
  end

• Page 48, Listing 3.1

  require 'config'

  should read

  require File.join(File.dirname(__FILE__), 'config')

• Page 49, First code snippet

  Replace

  def save_tweets_for(term)
    Twitter::Search.new.containing(term).each do |tweet|
      @tweets_found  += 1
      tweet_with_tag = tweet.to_hash.merge!({"tags" => [term]})
      @tweets.save(tweet_with_tag)
    end
  end

  with

  def save_tweets_for(term)
    Twitter.search(term).each do |tweet|
      @tweets_found  += 1
      tweet_with_tag = tweet.to_hash.merge!({"tags" => [term]})
      @tweets.save(tweet_with_tag)
    end
  end

• Page 49, Second code snippet

  Replace

  require 'config'
  require 'archiver'

  with

  require File.join(File.dirname(__FILE__), 'config')
  require File.join(File.dirname(__FILE__), 'archiver')

• Page 49, Third code snippet

  ruby update.rb

  should read

  $ ruby update.rb

• Page 50, Listing 3.2

  Replace

  require 'config'

  with

  require File.join(File.dirname(__FILE__), 'config')

• Page 69, First and second paragraphs

  "Next, you insert 20..." should read "Next, you insert 40..."

  "Even though you've inserted 20..." should read "Even though you've inserted 40..."

• Page 78, Final code snippet

  Replace

  category = db.categories.findOne({'slug': 'outdoors'})
  siblings = db.categories.find({'parent_id': category['_id']})
  products = db.products.find({'category_id': category['_id']}).
                              skip((page_number - 1) * 12).
                              limit(12).
                              sort({helpful_votes: -1})

  with

  category = db.categories.findOne({'slug': 'outdoors'})
  siblings = db.categories.find({'parent_id': category['parent_id']})
  products = db.products.find({'category_id': category['_id']}).
                              skip((page_number - 1) * 12).
                              limit(12).
                              sort({average_review: -1})

• Page 81, First code snippet

  Replace

  user_ids = db.orders.find({'line_items.sku': "9092",
  purchase_date: {'$gt': new Date(2009, 0, 1)}},
  {user_id: 1, _id: 0}).toArray().map(function(doc) { return doc['_id'] })
  users = db.users.find({_id: {$in: user_ids}})

  with

  user_ids = db.orders.find({'line_items.sku': "9092",
  purchase_date: {'$gt': new Date(2009, 0, 1)}},
  {user_id: 1, _id: 0}).toArray().map(function(doc) { return doc['user_id'] })
  users = db.users.find({_id: {$in: user_ids}})

• Page 85, Middle of the page.

  "Yoiu can query" should read "You can query."

• Page 94, First code snippet

  The line reading:

  emit(shipping_month, {order_total: this.sub_total, items_total: 0});

  should read:

  emit(shipping_month, {order_total: this.sub_total, items_total: 0});

• Page 94, Second code snippet

  The lines reading:

  var tmpTotal = 0;
  var tmpItems = 0;
  
  tmpTotal += doc.order_total;
  tmpItems += doc.items_total;
  
  return ( {order_total: tmpTotal, items_total: tmpItems} );

  should read:

  var tmpTotal = 0;
  var tmpItems = 0;
  
  values.forEach(function(doc) {
    tmpTotal += doc.order_total;
    tmpItems += doc.items_total;
  });
  
  return ( {order_total: tmpTotal, items_total: tmpItems} );

• Page 118, Syntax Note

  Replace the second code snippet with:

  db.products.update({price: {$lte: 10}}, {$addToSet: {tags: 'cheap'}})

• Page 124, 6.4.5, First paragraph, fifth sentence

  "which document are in RAM" should read "while documents are in RAM"

• Page 162, Third code snippet, sixth line

  > use bookstore switched to db bookstore

  should read

  > use bookstore
  switched to db bookstore

• Page 192, Fouth code snippet

  > rs.add("arete:30000")
  > rs.add("arete:30001", {arbiterOnly: true})

  should read

  > rs.add("arete:30001")
  > rs.add("arete:30002", {arbiterOnly: true})

• Page 192, Fifth code snippet

  $ mongo arete:30100
  > rs.initiate()
  > rs.add("arete:30100")
  > rs.add("arete:30101", {arbiterOnly: true})

  should read

  $ mongo arete:30100
  > rs.initiate()
  > rs.add("arete:30101")
  > rs.add("arete:30102", {arbiterOnly: true})

• Page 195, 9.2.2, Second code snippet

  The line

  @col  = @con['cloud']['spreadsheets']

  should read

  @col  = @con['cloud-docs']['spreadsheets']

• Page 222, Fourth code snippet

  mongod hard nofile 2048
            mongod hard nofile 10240

  should read

  mongodb soft nofile 2048
            mongodb hard nofile 10240

• Page 241, Code snippet

   > mongo.tz

  should read

   > mongo.tgz

• Page 244, First paragraph, first sentence

  "There two ways" should read "There are two ways"

• Page 252, First code snippet

  username: "plotinus"

  should read

  username: "kbanker"

  This then matches figure B.1.

• Page 262, C.2, first paragraph, last sentence

  "serve these object as well" should read "serve these objects as well"