haskell - 分析/改进内存使用和/或 GC 时间

Question

原装

我正在尝试聚合一个 CSV 文件并遇到 [我认为是] 过多的内存使用和/或 GC 工作。当组的数量增加时，问题似乎就会出现。当key为数百或数千时没有问题，但当key达到数万时，很快就开始在GC中花费大部分时间。

更新

从Data.ByteString.Lazy.ByteString搬家至 Data.ByteString.Short.ShortByteString显着减少了内存消耗(达到我认为合理的水平)。然而，花费在 GC 上的时间似乎仍然比我预期的要多得多。我是从 Data.HashMap.Strict.HashMap 搬来的至 Data.HashTable.ST.Basic.HashTable查看ST中是否有突变会有所帮助，但似乎没有。以下是当前完整的测试代码，包括generateFile创建测试样本:

{-# LANGUAGE OverloadedStrings #-}

module Main where

import System.IO (withFile, IOMode(WriteMode))
import qualified System.Random as Random

import qualified Data.ByteString.Short as BSS
import qualified Data.ByteString.Lazy.Char8 as BL
import qualified Data.Vector as V
import qualified Data.Vector.Mutable as MV
import qualified Control.Monad.ST as ST

import qualified Data.HashTable.ST.Basic as HT
import qualified Data.HashTable.Class as HT (toList)
import Data.Hashable (Hashable, hashWithSalt)

import Data.List (unfoldr)

import qualified Data.Traversable as T
import Control.Monad (forM_)

instance Hashable a => Hashable (V.Vector a) where
  hashWithSalt s = hashWithSalt s . V.toList

data CSVFormat = CSVFormat {
  csvSeparator :: Char,
  csvWrapper :: Char
}

readCSV :: CSVFormat -> Int -> FilePath -> IO [V.Vector BSS.ShortByteString]
readCSV format skip filepath = BL.readFile filepath >>= return . parseCSV format skip

parseCSV :: CSVFormat -> Int -> BL.ByteString -> [V.Vector BSS.ShortByteString]
parseCSV (CSVFormat sep wrp) skp = drop skp . unfoldr (\bs -> if BL.null bs then Nothing else Just (apfst V.fromList (parseLine bs)))
  where
    {-# INLINE apfst #-}
    apfst f (x,y) = (f x,y)

    {-# INLINE isCr #-}
    isCr c = c == '\r'

    {-# INLINE isLf #-}
    isLf c = c == '\n'

    {-# INLINE isSep #-}
    isSep c = c == sep || isLf c || isCr c

    {-# INLINE isWrp #-}
    isWrp c = c == wrp

    {-# INLINE parseLine #-}
    parseLine :: BL.ByteString -> ([BSS.ShortByteString], BL.ByteString)
    parseLine bs =
      let (field,bs') = parseField bs in
      case BL.uncons bs' of
        Just (c,bs1)
          | isLf c -> (field : [],bs1)
          | isCr c ->
              case BL.uncons bs1 of
                Just (c,bs2) | isLf c -> (field : [],bs2)
                _ -> (field : [],bs1)
          | otherwise -> apfst (field :) (parseLine bs1)
        Nothing -> (field : [],BL.empty)

    {-# INLINE parseField #-}
    parseField :: BL.ByteString -> (BSS.ShortByteString, BL.ByteString)
    parseField bs =
      case BL.uncons bs of
        Just (c,bs')
          | isWrp c -> apfst (BSS.toShort . BL.toStrict . BL.concat) (parseEscaped bs')
          | otherwise -> apfst (BSS.toShort . BL.toStrict) (BL.break isSep bs)
        Nothing -> (BSS.empty,BL.empty)

    {-# INLINE parseEscaped #-}
    parseEscaped :: BL.ByteString -> ([BL.ByteString], BL.ByteString)
    parseEscaped bs =
      let (chunk,bs') = BL.break isWrp bs in
      case BL.uncons bs' of
        Just (_,bs1) ->
          case BL.uncons bs1 of
            Just (c,bs2)
              | isWrp c -> apfst (\xs -> chunk : BL.singleton wrp : xs) (parseEscaped bs2)
              | otherwise -> (chunk : [],bs1)
            Nothing -> (chunk : [],BL.empty)
        Nothing -> error "EOF within quoted string"

aggregate :: [Int]
          -> Int
          -> [V.Vector BSS.ShortByteString]
          -> [V.Vector BSS.ShortByteString]
aggregate groups size records =
  let indices = [0..size - 1] in

  ST.runST $ do
    state <- HT.new

    forM_ records (\record -> do
        let key = V.fromList (map (\g -> record V.! g) groups)

        existing <- HT.lookup state key
        case existing of
          Just x ->
            forM_ indices (\i -> do
                current <- MV.read x i
                MV.write x i $! const current (record V.! i)
              )
          Nothing -> do
            x <- MV.new size
            forM_ indices (\i -> MV.write x i $! record V.! i)
            HT.insert state key x
      )

    HT.toList state >>= T.traverse V.unsafeFreeze . map snd

filedata :: IO ([Int],Int,[V.Vector BSS.ShortByteString])
filedata = do
  records <- readCSV (CSVFormat ',' '"') 1 "file.csv"
  return ([0,1,2],18,records)

main :: IO ()
main = do
  (key,len,records) <- filedata
  print (length (aggregate key len records))

generateFile :: IO ()
generateFile = do
  withFile "file.csv" WriteMode $ \handle -> do
    forM_ [0..650000] $ \_ -> do
      x <- BL.pack . show . truncate . (* 15 ) <$> (Random.randomIO :: IO Double)
      y <- BL.pack . show . truncate . (* 50 ) <$> (Random.randomIO :: IO Double)
      z <- BL.pack . show . truncate . (* 200) <$> (Random.randomIO :: IO Double)
      BL.hPut handle (BL.intercalate "," (x:y:z:replicate 15 (BL.replicate 20 ' ')))
      BL.hPut handle "\n"

我收到以下分析结果:

17,525,392,208 bytes allocated in the heap
27,394,021,360 bytes copied during GC
   285,382,192 bytes maximum residency (129 sample(s))
     3,714,296 bytes maximum slop
           831 MB total memory in use (0 MB lost due to fragmentation)

                                   Tot time (elapsed)  Avg pause  Max pause
Gen  0       577 colls,     0 par    1.576s   1.500s     0.0026s    0.0179s
Gen  1       129 colls,     0 par   25.335s  25.663s     0.1989s    0.2889s

TASKS: 3 (1 bound, 2 peak workers (2 total), using -N1)

SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

INIT    time    0.000s  (  0.002s elapsed)
MUT     time   11.965s  ( 23.939s elapsed)
GC      time   15.148s  ( 15.400s elapsed)
RP      time    0.000s  (  0.000s elapsed)
PROF    time   11.762s  ( 11.763s elapsed)
EXIT    time    0.000s  (  0.088s elapsed)
Total   time   38.922s  ( 39.429s elapsed)

Alloc rate    1,464,687,582 bytes per MUT second

Productivity  30.9% of total user, 30.5% of total elapsed

gc_alloc_block_sync: 0
whitehole_spin: 0
gen[0].sync: 0
gen[1].sync: 0

以及以下堆可视化:

Answer 1

原来是V.!调用不够严格。用 indexM 替换它们大大减少了内存消耗。