String#hash is not stable across processes :<

We need to implement our own hash functions for splitting
databases across multiple files.  This was totally fucking up
Rainbows!

8 files changed, 70 insertions, 5 deletions

diff --git a/lib/metropolis.rb b/lib/metropolis.rb
index c38d4af..0af1465 100644
--- a/lib/metropolis.rb
+++ b/lib/metropolis.rb
@@ -9,6 +9,7 @@ module Metropolis
   autoload :TC, 'metropolis/tc'
   autoload :Hash, 'metropolis/hash'
   autoload :TDB, 'metropolis/tdb'
+  autoload :MultiHash, 'metropolis/multi_hash'
 
   def self.new(opts = {})
     opts = opts.dup
@@ -19,6 +20,7 @@ module Metropolis
       @query = @uri.query ? Rack::Utils.parse_query(@uri.query) : nil
       @path_pattern = opts[:path_pattern]
       @path = @uri.path if @uri.path != '/'
+      @multi_hash = opts[:multi_hash]
     end
 
     base = case uri.scheme
diff --git a/lib/metropolis/multi_hash.rb b/lib/metropolis/multi_hash.rb
new file mode 100644
index 0000000..65ed6fe
--- /dev/null
+++ b/lib/metropolis/multi_hash.rb
@@ -0,0 +1,24 @@
+# -*- encoding: binary -*-
+module Metropolis::MultiHash
+  autoload :Digest, 'metropolis/multi_hash/digest'
+  autoload :ToI, 'metropolis/multi_hash/to_i'
+
+  def self.extended(obj)
+    sym = obj.instance_eval {
+      case @multi_hash.to_s
+      when /\Ato_i/
+        extend Metropolis::MultiHash::ToI
+      when /\Adigest_/
+        extend Metropolis::MultiHash::Digest
+      when /\Atdb_hash_/
+        extend TDB::HashFunctions
+      end
+      @multi_hash
+    }
+    obj.respond_to?(sym) or
+      raise ArgumentError, "multi_hash=#{sym} not supported"
+    (class << obj; self; end).instance_eval do
+      alias_method :multi_hash, sym
+    end
+  end
+end
diff --git a/lib/metropolis/multi_hash/digest.rb b/lib/metropolis/multi_hash/digest.rb
new file mode 100644
index 0000000..974d7ac
--- /dev/null
+++ b/lib/metropolis/multi_hash/digest.rb
@@ -0,0 +1,23 @@
+# -*- encoding: binary -*-
+require 'digest'
+module Metropolis::MultiHash::Digest
+  def digest_sha1(key)
+    ::Digest::SHA1.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_md5(key)
+    ::Digest::MD5.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha256(key)
+    ::Digest::SHA256.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha384(key)
+    ::Digest::SHA384.digest(key)[0,4].unpack("N")[0]
+  end
+
+  def digest_sha512(key)
+    ::Digest::SHA512.digest(key)[0,4].unpack("N")[0]
+  end
+end
diff --git a/lib/metropolis/multi_hash/to_i.rb b/lib/metropolis/multi_hash/to_i.rb
new file mode 100644
index 0000000..69b2819
--- /dev/null
+++ b/lib/metropolis/multi_hash/to_i.rb
@@ -0,0 +1,12 @@
+# -*- encoding: binary -*-
+# simple "hashing" method which converts keys to integers,
+# this may be useful for databases that only store numeric keys
+module Metropolis::MultiHash::ToI
+  def to_i(key)
+    key.to_i
+  end
+
+  def to_i_16(key)
+    key.to_i(16)
+  end
+end
diff --git a/lib/metropolis/tc/hdb.rb b/lib/metropolis/tc/hdb.rb
index d0833f8..e63b015 100644
--- a/lib/metropolis/tc/hdb.rb
+++ b/lib/metropolis/tc/hdb.rb
@@ -68,6 +68,8 @@ module Metropolis::TC::HDB
       end
       [ hdb, path ]
     end
+    @multi_hash ||= :digest_sha1
+    extend Metropolis::MultiHash
     extend(RO) if @readonly
     extend(EX) if @exclusive
   end
@@ -77,7 +79,7 @@ module Metropolis::TC::HDB
   end
 
   def writer(key, &block)
-    hdb, path = @dbv[key.hash % @nr_slots]
+    hdb, path = @dbv[multi_hash(key) % @nr_slots]
     hdb.open(path, @wr_flags) or ex!(:open, hdb)
     yield hdb
     ensure
@@ -85,7 +87,7 @@ module Metropolis::TC::HDB
   end
 
   def reader(key)
-    hdb, path = @dbv[key.hash % @nr_slots]
+    hdb, path = @dbv[multi_hash(key) % @nr_slots]
     hdb.open(path, @rd_flags) or ex!(:open, hdb)
     yield hdb
     ensure
diff --git a/lib/metropolis/tc/hdb/ex.rb b/lib/metropolis/tc/hdb/ex.rb
index 5bc7f39..d205a76 100644
--- a/lib/metropolis/tc/hdb/ex.rb
+++ b/lib/metropolis/tc/hdb/ex.rb
@@ -11,7 +11,7 @@ module Metropolis::TC::HDB::EX
   end
 
   def reader(key)
-    yield @ex_dbv[key.hash % @nr_slots]
+    yield @ex_dbv[multi_hash(key) % @nr_slots]
   end
 
   alias_method :writer, :reader
diff --git a/lib/metropolis/tc/hdb/ro.rb b/lib/metropolis/tc/hdb/ro.rb
index 62ededc..72fa968 100644
--- a/lib/metropolis/tc/hdb/ro.rb
+++ b/lib/metropolis/tc/hdb/ro.rb
@@ -14,6 +14,6 @@ module Metropolis::TC::HDB::RO
   end
 
   def reader(key)
-    yield @ro_dbv[key.hash % @nr_slots]
+    yield @ro_dbv[multi_hash(key) % @nr_slots]
   end
 end
diff --git a/lib/metropolis/tdb/multi.rb b/lib/metropolis/tdb/multi.rb
index b22e63b..68c8bf5 100644
--- a/lib/metropolis/tdb/multi.rb
+++ b/lib/metropolis/tdb/multi.rb
@@ -2,6 +2,8 @@
 module Metropolis::TDB::Multi
   def self.extended(obj)
     obj.instance_eval do
+      @multi_hash ||= :tdb_hash_murmur2
+      extend Metropolis::MultiHash
       @dbv = (0...@nr_slots).to_a.map do |slot|
         path = sprintf(@path_pattern, slot)
         ::TDB.new(path, @tdb_opts)
@@ -10,7 +12,7 @@ module Metropolis::TDB::Multi
   end
 
   def db(key, &block)
-    yield @dbv[key.hash % @nr_slots]
+    yield @dbv[multi_hash(key) % @nr_slots]
   end
 
   def close!