Enable ordinary-index building without a page count bound

Author: jeltsch

lsm-tree.cabal

@@ -157,6 +157,7 @@ library
     Database.LSMTree.Internal.UniqCounter
     Database.LSMTree.Internal.Unsliced
     Database.LSMTree.Internal.Vector
+    Database.LSMTree.Internal.Vector.Growing
     Database.LSMTree.Internal.WriteBuffer
     Database.LSMTree.Internal.WriteBufferBlobs
     Database.LSMTree.Monoidal

src/Database/LSMTree/Internal/IndexOrdinaryAcc.hs

@@ -17,11 +17,6 @@ import           Prelude hiding (take)
 
 import           Control.Exception (assert)
 import           Control.Monad.ST.Strict (ST)
-import           Data.Primitive.PrimVar (PrimVar, newPrimVar, readPrimVar,
-                     writePrimVar)
-import           Data.Vector (force, take, unsafeFreeze)
-import           Data.Vector.Mutable (MVector)
-import qualified Data.Vector.Mutable as Mutable (unsafeNew, write)
 import qualified Data.Vector.Primitive as Primitive (Vector, length)
 import           Data.Word (Word16, Word8)
 import           Database.LSMTree.Internal.Chunk (Baler, Chunk, createBaler,
@@ -33,33 +28,28 @@ import           Database.LSMTree.Internal.IndexOrdinary
 import           Database.LSMTree.Internal.Serialise
                      (SerialisedKey (SerialisedKey'))
 import           Database.LSMTree.Internal.Vector (byteVectorFromPrim)
+import           Database.LSMTree.Internal.Vector.Growing (GrowingVector)
+import qualified Database.LSMTree.Internal.Vector.Growing as Growing (append,
+                     freeze, new)
 
 {-|
     A general-purpose fence pointer index under incremental construction.
 
-    A value @IndexOrdinaryAcc buffer keyCountRef baler@ denotes a partially
-    constructed index with the following properties:
-
-      * The keys that the index assigns to pages are stored as a prefix of the
-        mutable vector @buffer@.
-      * The reference @keyCountRef@ points to the number of those keys.
-      * The @baler@ object is used by the index for incremental output of the
-        serialised key list.
+    A value @IndexOrdinaryAcc lastKeys baler@ denotes a partially constructed
+    index that assigns keys to pages according to @lastKeys@ and uses @baler@
+    for incremental output of the serialised key list.
 -}
 data IndexOrdinaryAcc s = IndexOrdinaryAcc
-                              !(MVector s SerialisedKey)
-                              !(PrimVar s Int)
+                              !(GrowingVector s SerialisedKey)
                               !(Baler s)
 
 -- | Creates a new, initially empty, index.
-new :: Int                       -- ^ Maximum number of keys
+new :: Int                       -- ^ Initial size of the key buffer
     -> Int                       -- ^ Minimum chunk size in bytes
     -> ST s (IndexOrdinaryAcc s) -- ^ Construction of the index
-new maxKeyCount minChunkSize = assert (maxKeyCount >= 0)      $
-                               IndexOrdinaryAcc              <$>
-                               Mutable.unsafeNew maxKeyCount <*>
-                               newPrimVar 0                  <*>
-                               createBaler minChunkSize
+new initialKeyBufferSize minChunkSize = IndexOrdinaryAcc                 <$>
+                                        Growing.new initialKeyBufferSize <*>
+                                        createBaler minChunkSize
 
 {-|
     Appends keys to the key list of an index and outputs newly available chunks
@@ -69,26 +59,18 @@ new maxKeyCount minChunkSize = assert (maxKeyCount >= 0)      $
     word may result in a corrupted serialised key list.
 -}
 append :: Append -> IndexOrdinaryAcc s -> ST s (Maybe Chunk)
-append instruction (IndexOrdinaryAcc buffer keyCountRef baler)
+append instruction (IndexOrdinaryAcc lastKeys baler)
     = case instruction of
           AppendSinglePage _ key -> do
-              keyCount <- readPrimVar keyCountRef
-              Mutable.write buffer keyCount key
-              writePrimVar keyCountRef (succ keyCount)
+              Growing.append lastKeys 1 key
               feedBaler (keyListElem key) baler
           AppendMultiPage key overflowPageCount -> do
-              keyCount <- readPrimVar keyCountRef
               let
 
                   pageCount :: Int
                   !pageCount = succ (fromIntegral overflowPageCount)
 
-                  keyCount' :: Int
-                  !keyCount' = keyCount + pageCount
-
-              mapM_ (flip (Mutable.write buffer) key)
-                    [keyCount .. pred keyCount']
-              writePrimVar keyCountRef keyCount'
+              Growing.append lastKeys pageCount key
               feedBaler (concat (replicate pageCount (keyListElem key))) baler
     where
 
@@ -112,8 +94,7 @@ append instruction (IndexOrdinaryAcc buffer keyCountRef baler)
     @index@ is not used afterwards.
 -}
 unsafeEnd :: IndexOrdinaryAcc s -> ST s (Maybe Chunk, IndexOrdinary)
-unsafeEnd (IndexOrdinaryAcc buffer keyCountRef baler) = do
-    keyCount <- readPrimVar keyCountRef
-    keys <- force <$> take keyCount <$> unsafeFreeze buffer
+unsafeEnd (IndexOrdinaryAcc lastKeys baler) = do
+    keys <- Growing.freeze lastKeys
     remnant <- unsafeEndBaler baler
     return (remnant, IndexOrdinary keys)

src/Database/LSMTree/Internal/Vector/Growing.hs

@@ -0,0 +1,120 @@
+{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
+
+{- HLINT ignore "Avoid restricted alias" -}
+
+-- | Vectors with support for appending elements.
+module Database.LSMTree.Internal.Vector.Growing
+(
+    GrowingVector,
+    new,
+    append,
+    freeze
+)
+where
+
+import           Prelude hiding (init, last, length)
+
+import           Control.Monad (when)
+import           Control.Monad.ST.Strict (ST)
+import           Data.Primitive.PrimVar (PrimVar, newPrimVar, readPrimVar,
+                     writePrimVar)
+import           Data.STRef.Strict (STRef, newSTRef, readSTRef, writeSTRef)
+import           Data.Vector (Vector)
+import qualified Data.Vector as Mutable (freeze)
+import           Data.Vector.Mutable (MVector)
+import qualified Data.Vector.Mutable as Mutable (grow, length, new, set, slice,
+                     take)
+
+{-|
+    A vector with support for appending elements.
+
+    Internally, the elements of a growing vector are stored in a buffer. This
+    buffer is automatically enlarged whenever this is needed for storing
+    additional elements. On each such enlargement, the size of the buffer is
+    multiplied by a power of 2, whose exponent is chosen just big enough to make
+    the final buffer size at least as high as the new vector length.
+
+    Note that, while buffer sizes and vector lengths are represented as 'Int'
+    values internally, the above-described buffer enlargement scheme has the
+    consequence that the largest possible buffer size and thus the largest
+    possible vector length may not be the maximum 'Int' value. That said, they
+    are always greater than half the maximum 'Int' value, which should be enough
+    for all practical purposes.
+-}
+data GrowingVector s a = GrowingVector
+                             !(STRef s (MVector s a)) -- Reference to the buffer
+                             !(PrimVar s Int)         -- Reference to the length
+
+-- | Creates a new, initially empty, vector.
+new :: Int                      -- ^ Initial buffer size
+    -> ST s (GrowingVector s a) -- ^ Construction of the vector
+new illegalInitialBufferSize | illegalInitialBufferSize <= 0
+    = error "Initial buffer size not positive"
+new initialBufferSize
+    = do
+        buffer <- Mutable.new initialBufferSize
+        bufferRef <- newSTRef $! buffer
+        lengthRef <- newPrimVar 0
+        return (GrowingVector bufferRef lengthRef)
+
+{-|
+    Appends a value a certain number of times to a vector. If a negative number
+    is provided as the count, the vector is not changed.
+-}
+append :: forall s a . GrowingVector s a -> Int -> a -> ST s ()
+append _ pseudoCount _ | pseudoCount <= 0
+    = return ()
+append (GrowingVector bufferRef lengthRef) count val
+    = do
+          length <- readPrimVar lengthRef
+          makeRoom
+          buffer' <- readSTRef bufferRef
+          Mutable.set (Mutable.slice length count buffer') val
+    where
+
+    makeRoom :: ST s ()
+    makeRoom = do
+        length <- readPrimVar lengthRef
+        when (count > maxBound - length) (error "New length too large")
+        buffer <- readSTRef bufferRef
+        let
+
+            bufferSize :: Int
+            !bufferSize = Mutable.length buffer
+
+            length' :: Int
+            !length' = length + count
+
+        when (bufferSize < length') $ do
+            let
+
+                higherBufferSizes :: [Int]
+                higherBufferSizes = tail (init ++ [last]) where
+
+                    init :: [Int]
+                    last :: Int
+                    (init, last : _) = span (<= maxBound `div` 2) $
+                                       iterate (* 2) bufferSize
+                    {-NOTE:
+                        In order to prevent overflow, we have to start with the
+                        current buffer size here, although we know that it is
+                        not sufficient.
+                    -}
+
+                sufficientBufferSizes :: [Int]
+                sufficientBufferSizes = dropWhile (< length') higherBufferSizes
+
+            case sufficientBufferSizes of
+                []
+                    -> error "No sufficient buffer size available"
+                bufferSize' : _
+                    -> Mutable.grow buffer (bufferSize' - bufferSize) >>=
+                       (writeSTRef bufferRef $!)
+        writePrimVar lengthRef length'
+
+-- | Turns a growing vector into an ordinary vector.
+freeze :: GrowingVector s a -> ST s (Vector a)
+freeze (GrowingVector bufferRef lengthRef) = do
+    buffer <- readSTRef bufferRef
+    length <- readPrimVar lengthRef
+    Mutable.freeze (Mutable.take length buffer)

test/Test/Database/LSMTree/Internal/IndexOrdinary.hs

@@ -225,13 +225,6 @@ serialisedIndex entryCount lastKeys
 
 -- ** Construction via appending
 
--- Yields the number of keys that an append operation adds to an index.
-appendedKeysCount :: Append -> Int
-appendedKeysCount (AppendSinglePage _ _)
-    = 1
-appendedKeysCount (AppendMultiPage _ overflowPageCount)
-    = succ (fromIntegral overflowPageCount)
-
 -- Yields the keys that an append operation adds to an index.
 appendedKeys :: Append -> [SerialisedKey]
 appendedKeys (AppendSinglePage _ lastKey)
@@ -265,7 +258,7 @@ lastKeysBlockFromAppends appends = lastKeysBlock where
 -}
 incrementalConstruction :: [Append] -> (IndexOrdinary, Primitive.Vector Word8)
 incrementalConstruction appends = runST $ do
-    acc <- new keyCount minChunkSize
+    acc <- new initialKeyBufferSize minChunkSize
     commonChunks <- mapM (flip append acc) appends
     (remnant, unserialised) <- unsafeEnd acc
     let
@@ -277,8 +270,12 @@ incrementalConstruction appends = runST $ do
     return (unserialised, serialised)
     where
 
-    keyCount :: Int
-    keyCount = sum (map appendedKeysCount appends)
+    {-
+        We do not need to vary the initial key buffer size, since we are not
+        testing growing vectors here.
+    -}
+    initialKeyBufferSize :: Int
+    initialKeyBufferSize = 0x100
 
     {-
         We do not need to vary the minimum chunk size, since we are not testing