Hi Maciej, Thanks for looking in to this.
From: Maciej Piechotka
On Fri, 2011-02-18 at 17:27 +0300, Michael A Baikov wrote:
I am trying to play with iteratee making parser for squid log files, but found that my code do not run in constant space when it tries to process compressed log files. So i simplified my code down to this snippet:
import Data.ByteString (ByteString) import Data.Iteratee as I import Data.Iteratee.Char import Data.Iteratee.ZLib import System
main = do args <- getArgs let fname = args !! 0 let blockSize = read $ args !! 1
fileDriver (leak blockSize) fname >>= print
leak :: Int -> Iteratee ByteString IO () leak blockSize = joinIM $ enumInflate GZip defaultDecompressParams chunkedRead where consChunk :: Iteratee ByteString IO String consChunk = (joinI $ I.take blockSize I.length) >>= return . show
chunkedRead :: Iteratee ByteString IO () chunkedRead = joinI $ convStream consChunk printLines
First argument - file name (/var/log/messages.1.gz will do) second - size of block to consume input. with low size (10 bytes) of consumed blocks it leaks very fast, with larger blocks (~10000) it works almost without leaks.
So. Is it bugs within my code, or iteratee-compress should behave differently?
After looking into problem (or rather onto your code) - the problem have nothing to do with iteratee-compress I believe. I get similar behaviour and results when I replace "joinIM $ enumInflate GZip defaultDecompressParams chunkedRead" by chunkedRead. (The memory is smaller but it is due to decompression not iteratee fault).
This is due to "printLines". Whether it's a bug depends on what the correct behavior of "printLines" should be. "printLines" currently only prints lines that are terminated by an EOL (either "\n" or "\r\n"). This means that it needs to hold on to the entire stream received until it finds EOL, and then prints the stream, or drops it if it reaches EOF first. In your case, the stream generated by "convStream consChunk printLines" is just a stream of numbers without any EOL, where the length is dependent on the specified block size. This causes the space leak. If I change the behavior of "printLines" to print lines that aren't terminated by EOL, the leak could be fixed. Whether that behavior is more useful than the present, I don't know. Alternatively, if you insert some newlines into your stream this could be improved as well. As a result of investigating this, I realized that Data.Iteratee.ListLike.break can be very inefficient in cases where the predicate is not satisfied relatively early. I should actually provide an enumeratee interface for it. So thanks very much for (indirectly) suggesting that. Cheers, John L