finish bloom filters

Add tuning, docs, etc.

Not sure if status is the right place to remote size.. perhaps unused
should report the size and also warn if it sees more keys than the bloom
filter allows?

Command/Status.hs

@@ -76,6 +76,7 @@ slow_stats =
 	, local_annex_size
 	, known_annex_keys
 	, known_annex_size
+	, bloom_info
 	, backend_usage
 	]
 
@@ -127,7 +128,7 @@ remote_list level desc = stat n $ nojson $ lift $ do
 	return $ if null s then "0" else show (length rs) ++ "\n" ++ beginning s
 	where
 		n = desc ++ " repositories"
-
+	
 local_annex_size :: Stat
 local_annex_size = stat "local annex size" $ json id $
 	showSizeKeys <$> cachedPresentData
@@ -136,6 +137,22 @@ local_annex_keys :: Stat
 local_annex_keys = stat "local annex keys" $ json show $
 	countKeys <$> cachedPresentData
 
+bloom_info :: Stat
+bloom_info = stat "bloom filter size" $ json id $ do
+	localkeys <- countKeys <$> cachedPresentData
+	capacity <- fromIntegral <$> lift Command.Unused.bloomCapacity
+	let note = aside $
+		if localkeys >= capacity
+		then "appears too small for this repository; adjust annex.bloomcapacity"
+		else "has room for " ++ show (capacity - localkeys) ++ " more local annex keys"
+
+	-- Two bloom filters are used at the same time, so double the size
+	-- of one.
+	size <- roughSize memoryUnits True . (* 2) . fromIntegral . fst <$>
+		lift Command.Unused.bloomBitsHashes
+
+	return $ size ++ note
+
 known_annex_size :: Stat
 known_annex_size = stat "known annex size" $ json id $
 	showSizeKeys <$> cachedReferencedData

Command/Unused.hs

@@ -29,6 +29,7 @@ import qualified Git.Command
 import qualified Git.Ref
 import qualified Git.LsFiles as LsFiles
 import qualified Git.LsTree as LsTree
+import qualified Git.Config
 import qualified Backend
 import qualified Remote
 import qualified Annex.Branch
@@ -182,6 +183,22 @@ exclude smaller larger = S.toList $ remove larger $ S.fromList smaller
 	where
 		remove a b = foldl (flip S.delete) b a
 
+{- A bloom filter capable of holding half a million keys with a
+ - false positive rate of 1 in 1000 uses around 8 mb of memory,
+ - so will easily fit on even my lowest memory systems.
+ -}
+bloomCapacity :: Annex Int
+bloomCapacity = fromMaybe 500000 . readish
+	<$> fromRepo (Git.Config.get "annex.bloomcapacity" "")
+bloomAccuracy :: Annex Int
+bloomAccuracy = fromMaybe 1000 . readish
+	<$> fromRepo (Git.Config.get "annex.bloomaccuracy" "")
+bloomBitsHashes :: Annex (Int, Int)
+bloomBitsHashes = do
+	capacity <- bloomCapacity
+	accuracy <- bloomAccuracy
+	return $ suggestSizing capacity (1/ fromIntegral accuracy)
+
 {- Creates a bloom filter, and runs an action, such as withKeysReferenced,
  - to populate it.
  -
@@ -193,12 +210,7 @@ exclude smaller larger = S.toList $ remove larger $ S.fromList smaller
  -}
 genBloomFilter :: Hashable t => (v -> t) -> ((v -> Annex ()) -> Annex b) -> Annex (Bloom t)
 genBloomFilter convert populate = do
-	-- A bloom filter capable of holding half a million keys with a
-	-- false positive rate of 0.1% uses around 8 mb of memory.
-	-- TODO: make this configurable, for the really large repos,
-	-- or really low false positive rates.
-	let (numbits, numhashes) = suggestSizing 500000 0.001
-
+	(numbits, numhashes) <- bloomBitsHashes
 	bloom <- lift $ newMB (cheapHashes numhashes) numbits
 	_ <- populate $ \v -> lift $ insertMB bloom (convert v)
 	lift $ unsafeFreezeMB bloom