[Haskell-beginners] Warp and Yesod benchmark puzzle

[Krzysztof Skrzętnicki]

makeSessionBackend calls "getKey" from clientsession:

http://hackage.haskell.org/packages/archive/clientsession/0.8.0/doc/html/src/Web-ClientSession.html#getKey

Looking at that function no wonder it is a bottleneck:

-- | Get a key from the given text file.---- If the file does not
exist or is corrupted a random key will-- be generated and stored in
that file.getKey :: FilePath     -- ^ File name where key is stored.
    -> IO Key       -- ^ The actual key.getKey keyFile = do    exists
<- doesFileExist keyFile    if exists        then S.readFile keyFile
>>= either (const newKey) return . initKey        else newKey  where
 newKey = do        (bs, key') <- randomKey        S.writeFile keyFile
bs        return key'


Plenty of syscalls, reading and parsing the same file over and over again.
Perhaps the default should be to store the key within the foundation
datatype at startup?

Best regards,
Krzysztof Skrzętnicki

On Sat, Sep 1, 2012 at 10:37 AM, Lorenzo Bolla <lbolla at gmail.com> wrote:

> On Fri, Aug 31, 2012 at 10:13:20PM -0300, Felipe Almeida Lessa wrote:
> > [Forwarding to Yesod's mailing list as well.  I'll copy all of the
> > original text below for those who aren't on haskell-beginners.]
> >
> > On Fri, Aug 31, 2012 at 11:24 AM, Lorenzo Bolla <lbolla at gmail.com>
> wrote:
> > > Hi all,
> > >
> > > This is a question specific to the Yesod framework, but simple enough
> > > (I hope) to be considered a beginner question...
> > >
> > > I am puzzled by the performance of these two very simple web-servers,
> > > one written in Warp and another written in Yesod:
> > >
> > > === YESOD ===
> > >
> > > {-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses,
> > > TemplateHaskell #-}
> > > import Yesod
> > >
> > > data HelloWorld = HelloWorld
> > >
> > > mkYesod "HelloWorld" [parseRoutes|
> > > / HomeR GET
> > > |]
> > >
> > > instance Yesod HelloWorld
> > >
> > > getHomeR :: Handler RepHtml
> > > getHomeR = defaultLayout [whamlet|$newline always
> > > Hello World!
> > > |]
> > >
> > > main :: IO ()
> > > -- main = warpDebug 3000 HelloWorld
> > > main = warp 3000 HelloWorld
> > >
> > > === WARP ===
> > >
> > > {-# LANGUAGE OverloadedStrings #-}
> > >
> > > import Network.Wai
> > > import Network.HTTP.Types
> > > import Network.Wai.Handler.Warp (run)
> > > import Data.ByteString.Lazy.Char8 ()
> > >
> > > app :: Application
> > > app _ = return $ responseLBS
> > >     status200
> > >     [("Content-Type", "text/html")]
> > >     "Hello, Warp!"
> > >
> > > main :: IO ()
> > > main = do
> > >     putStrLn "http://localhost:8080/"
> > >     run 8080 app
> > >
> > > ===
> > >
> > > I've tested both using httperf:
> > > $> httperf --hog --client=0/1 --server=localhost --port=3000 --uri=/
> > > --rate=1000 --send-buffer=4096 --recv-buffer=16384 --num-conns=100
> > > --num-calls=100 --burst-length=20
> > >
> > > and I got very different results:
> > >
> > > YESOD: Request rate: 4048.0 req/s (0.2 ms/req)
> > > WARP: Request rate: 33656.2 req/s (0.0 ms/req)
> > >
> > > Now, I understand that Yesod is expected to be slower than the "raw"
> > > Warp, but I wasn't expecting a 10x slowdown, especially for such a
> > > trivial Yesod app (no db, no auth, etc.).
> > >
> > > [
> > > Compilation command was: ghc -Wall -O2 --make yesod.hs
> > > $ yesod version
> > > yesod-core version:1.1.0
> > > ]
> > >
> > > What is going on?
> > >
> > > Thanks,
> > > L.
> >
> > This is actually a rather tricky and interesting question =).
> >
> > My knee-jerk reaction is "profile!".  Profiling will give you more
> > clues about where the time is being spent.
> >
> > As Bryce said, you're using defaultLayout and Hamlet, which should
> > slow things down.  Also, you're implicitly using clientsession, you
> > may try setting makeSessionBackend [1] to 'const $ return Nothing' and
> > see what kind of performance you get.
> >
> > Cheers!
> >
> > [1]
> http://hackage.haskell.org/packages/archive/yesod-core/1.1.1.1/doc/html/Yesod-Core.html#v:makeSessionBackend
> >
> > --
> > Felipe.
>
> Good catch Felipe!
> It looks like `makeSessionBackend` is horribly slow... These are the
> numbers on
> my box:
>
> Warp
>     10250 req/s
>
> Yesod
>     hamlet: 848 req/s
>     no-hamlet: 940 req/s (getHomeR = return ∘ RepPlain ∘ toContent $
> "Hello World!")
>     no-session: 8000 req/s (makeSessionBackend = const $ return Nothing)
>
> L.
>
> --
> Lorenzo Bolla
> http://lbolla.info
>
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