Nginx stops sending file after ~1.5mb ?

Igor Sysoev is at rambler-co.ru
Tue Jan 27 11:51:10 MSK 2009 

On Tue, Jan 27, 2009 at 10:42:57AM +0200, Yo'av Moshe wrote:

> Note I just compiled Cherokee 0.98. It is serving the file as it should
> using sendfile and epoll.

Have you tried this on the same host ?
Could you post strace ?

> On Mon, Jan 26, 2009 at 2:05 PM, Yo'av Moshe <bjesus at gmail.com> wrote:
> 
> > Hey, attached is my tcpdump log.
> > I've never used tcpdump before, so I hope the log is fine.
> > I used grep to show only the connections from my computer while running
> > 'wget http://www.noal.org.il/static/temp/hozer.pdf'.
> >
> > Hope this will lead us somewhere...
> >
> > Yo'av.
> >
> >
> > On Sun, Jan 25, 2009 at 9:21 PM, Igor Sysoev <is at rambler-co.ru> wrote:
> >
> >> On Sun, Jan 25, 2009 at 09:04:54PM +0200, Yo'av Moshe wrote:
> >>
> >> > Sendfile is now off, using select, and still the same...
> >> > http://pastebin.com/m2c3ea25b
> >>
> >> I have no idea, why it may be so.
> >>
> >> I see that select() returned event ("out [19]"):
> >>
> >> 28215 20:50:18 select(20, [10 19], [19], NULL, {0, 500000} <unfinished
> >> ...>
> >> 28215 20:50:18 <... select resumed> )   = 1 (out [19], left {0, 380000})
> >>
> >> However, at some stage select() did not return event, although the event
> >> is still active ("select(20, [10 19], [19], NULL ..."):
> >>
> >> 28215 20:50:18 gettimeofday({1232909418, 293895}, NULL) = 0
> >> 28215 20:50:18 writev(19,
> >> [{"\227\1\2\1\3\1\4\1\5\0\373\0\374\1\230\1\231\1\232\1\233\0\375\0\376\1\6\1\7\1\10\0"...,
> >> 9676}], 1) = 9676
> >> 28215 20:50:18 pread64(20,
> >> "\24\7\6#\"\'&\0214\22$63\1\6\25\24\26\27\02632654&#\"\6\3\226\204"...,
> >> 32768, 1605632) = 32768
> >> 28215 20:50:18 writev(19,
> >> [{"\24\7\6#\"\'&\0214\22$63\1\6\25\24\26\27\02632654&#\"\6\3\226\204"...,
> >> 32768}], 1) = 32768
> >> 28215 20:50:18 pread64(20, "\0 \0M\0o\0r\0i\0s\0o\0n\0\'\0s\0
> >> \0d\0i\0r\0e\0c"..., 32768, 1638400) = 32768
> >> 28215 20:50:18 writev(19, [{"\0 \0M\0o\0r\0i\0s\0o\0n\0\'\0s\0
> >> \0d\0i\0r\0e\0c"..., 32768}], 1) = 1716
> >> 28215 20:50:18 select(20, [10 19], [19], NULL, {0, 500000} <unfinished
> >> ...>
> >> 28215 20:50:18 <... select resumed> )   = 0 (Timeout)
> >>
> >> Could you run tcpdump of the session ?
> >>
> >> > Yo'av
> >> >
> >> > On Sun, Jan 25, 2009 at 7:33 PM, Igor Sysoev <is at rambler-co.ru> wrote:
> >> >
> >> > > On Sun, Jan 25, 2009 at 06:26:58PM +0200, Yo'av Moshe wrote:
> >> > >
> >> > > > Igor, I tried using select instead of poll, but I get the exact same
> >> > > > problem.
> >> > > >
> >> > > > Check my strace:
> >> > > > http://pastebin.com/m65056ec0
> >> > > >
> >> > > > I get the same thing with rtsig too.
> >> > > >
> >> > > > Hints?
> >> > > > Again, file is at http://www.noal.org.il/static/temp/hozer.pdf.
> >> Server
> >> > > is
> >> > > > using select now.
> >> > >
> >> > > According strace select() does not return event for socket 19 after
> >> > > sendfile64() sent 1651005 bytes:
> >> > >
> >> > > 25951 18:14:26 select(20, [7 8 16 19], [19], NULL, {60, 0} <unfinished
> >> ...>
> >> > > 25951 18:14:27 <... select resumed> )   = 1 (out [19], left {58,
> >> 790000})
> >> > >
> >> > > 25951 18:14:27 gettimeofday({1232900067, 890376}, NULL) = 0
> >> > > 25951 18:14:27 sendfile64(19, 20, [1509465], 440765 <unfinished ...>
> >> > > 25951 18:14:27 <... sendfile64 resumed> ) = 141540
> >> > > 25951 18:14:27 sendfile64(19, 20, [1651005], 299225 <unfinished ...>
> >> > > 25951 18:14:27 <... sendfile64 resumed> ) = -1 EAGAIN (Resource
> >> temporarily
> >> > > unavailable)
> >> > >
> >> > > 25951 18:14:27 select(20, [16 19], [19], NULL, {0, 500000} <unfinished
> >> ...>
> >> > > 25951 18:14:28 <... select resumed> )   = 0 (Timeout)
> >> > >
> >> > > As you have got the same issue with all methods (even with level
> >> triggered
> >> > > select()), I believe that the bug is in sendfile. You may try to turn
> >> > > it off even for the single file:
> >> > >
> >> > >    location = /static/temp/hozer.pdf {
> >> > >        sendfile off;
> >> > >    }
> >> > >
> >> > > In Linux 2.6.23 sendfile() has been rewritten to use splice framework.
> >> > > The bug may be introduced while rewriting.
> >> > >
> >> > > BTW, it seems that thttpd does not use sendfile.
> >> > >
> >> > > > Thanks...
> >> > > > Yo'av.
> >> > > >
> >> > > > On Fri, Jan 23, 2009 at 3:05 PM, Igor Sysoev <is at rambler-co.ru>
> >> wrote:
> >> > > >
> >> > > > > On Fri, Jan 23, 2009 at 02:35:00PM +0200, Yo'av Moshe wrote:
> >> > > > >
> >> > > > > > Thanks Igor.
> >> > > > > > I don't want to be rude, but I find it hard to believe that it's
> >> a
> >> > > kernel
> >> > > > > > bug.
> >> > > > > >
> >> > > > > > First, I'm using the default CentOS 5.2 kernel, it's seems to me
> >> > > pretty
> >> > > > > odd
> >> > > > > > that there's such a bug in it. CentOS is being used on a lot of
> >> > > servers,
> >> > > > > > some of them must be running nginx.
> >> > > > > >
> >> > > > > > Second, I tried serving the same file with thttpd, and it runs
> >> just
> >> > > fine.
> >> > > > > > http://195.28.180.147:40/temp/hozer.pdf
> >> > > > > > Note it's the exact same file which I cannot get from nginx:
> >> > > > > > http://www.noal.org.il/static/temp/hozer.pdf
> >> > > > > >
> >> > > > > > How come thttpd can serve the file just fine? If it's a kernel
> >> bug, I
> >> > > > > > thought it would happen with all of my servers.
> >> > > > > > If it's using some different way of sending the files which does
> >> not
> >> > > > > depend
> >> > > > > > on that epoll call - is there any way to configure nginx to use
> >> that
> >> > > as
> >> > > > > > well?
> >> > > > >
> >> > > > > I do not look modern thttpd, but according its change log, it has
> >> no
> >> > > > > epoll support. You may try different ways in nginx: you need to
> >> build
> >> > > it
> >> > > > >
> >> > > > >        --with-rtsig_module
> >> > > > >        --with-select_module
> >> > > > >        --with-poll_module
> >> > > > >
> >> > > > > and then choose method:
> >> > > > >
> >> > > > > events {
> >> > > > >     use  select;
> >> > > > >     #use  poll;
> >> > > > >     #use  rtsig;
> >> > > > > }
> >> > > > >
> >> > > > > Also, epoll has two modes: level triggered (default) and edge
> >> > > > > triggered (EPOLLET). nginx uses more effective edge triggered
> >> mode,
> >> > > > > lighttpd uses level triggered one. The bug may be in ET mode only.
> >> > > > >
> >> > > > > As to probabilty of kernel bugs: I saw them in FreeBSD (kqueue,
> >> > > sendfile),
> >> > > > > Linux (epoll), Solaris (event ports), and MacOSX (kqueue,
> >> sendfile).
> >> > > > >
> >> > > > > > Can I do anything to confirm that it's a kernel bug? If it is, I
> >> > > should
> >> > > > > > probably contact CentOS's maintainers.
> >> > > > >
> >> > > > > Your straces confirms this: nginx added socket to epoll and did
> >> not
> >> > > > > deleted it, nevertheless epoll does not send event.
> >> > > > >
> >> > > > > > Thank you, again.
> >> > > > > > Yo'av.
> >> > > > > >
> >> > > > > > On Wed, Jan 21, 2009 at 7:26 AM, Igor Sysoev <is at rambler-co.ru>
> >> > > wrote:
> >> > > > > >
> >> > > > > > > On Wed, Jan 21, 2009 at 01:52:53AM +0200, Yo'av Moshe wrote:
> >> > > > > > >
> >> > > > > > > > Igor, here's the new strace.
> >> > > > > > > > http://pastebin.com/m5129c54b
> >> > > > > > > >
> >> > > > > > > > Does the fact it works in low download rates still makes you
> >> > > think
> >> > > > > it's a
> >> > > > > > > > kernel issue?
> >> > > > > > >
> >> > > > > > > Yes, this is seems like a kernel issue. Kernel excatly said
> >> (with
> >> > > > > EAGAIN)
> >> > > > > > > that there is no place to output data, but never returned a
> >> new
> >> > > > > > > notification
> >> > > > > > > via epoll_wait() about free space:
> >> > > > > > >
> >> > > > > > > 21420 01:39:43 <... epoll_wait resumed> {{EPOLLOUT,
> >> {u32=153137960,
> >> > > > > > > u64=13811628390360331048}}}, 512, 60000) = 1
> >> > > > > > > 21420 01:39:43 gettimeofday({1232494783, 413764}, NULL) = 0
> >> > > > > > > 21420 01:39:43 sendfile64(20, 21, [1645625], 304605) = 40320
> >> > > > > > > 21420 01:39:43 sendfile64(20, 21, [1685945], 264285) = -1
> >> EAGAIN
> >> > > > > (Resource
> >> > > > > > > temporarily unavailable)
> >> > > > > > > 21420 01:39:43 epoll_wait(11,  <unfinished ...>
> >> > > > > > >
> >> > > > > > > This is probably some race condition inside kernel, that does
> >> not
> >> > > > > appear on
> >> > > > > > > low speed download.
> >> > > > > > >
> >> > > > > > > > Thank you, really!
> >> > > > > > > > And thanks, Kiril and Jeff, for confirming that!
> >> > > > > > > >
> >> > > > > > > > Yo'av.
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > On Tue, Jan 20, 2009 at 9:39 PM, Kiril Angov <
> >> > > kupokomapa at gmail.com>
> >> > > > > > > wrote:
> >> > > > > > > >
> >> > > > > > > > > wget http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > --2009-01-20 21:36:00--
> >> > > > > > > http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > Resolving www.noal.org.il... 195.28.180.147
> >> > > > > > > > > Connecting to www.noal.org.il|195.28.180.147|:80...
> >> connected.
> >> > > > > > > > > HTTP request sent, awaiting response... 200 OK
> >> > > > > > > > > Length: 1950230 (1.9M) [application/pdf]
> >> > > > > > > > > Saving to: `barvazi2.pdf'
> >> > > > > > > > >
> >> > > > > > > > > 81% [=====================================>         ]
> >> 1,596,665
> >> > > > > > > > > --.-K/s  eta 5s
> >> > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > > > wget -c http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > --2009-01-20 21:38:28--
> >> > > > > > > > > http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > Resolving www.noal.org.il... 195.28.180.147
> >> > > > > > > > > Connecting to www.noal.org.il|195.28.180.147|:80...
> >> connected.
> >> > > > > > > > > HTTP request sent, awaiting response... 206 Partial
> >> Content
> >> > > > > > > > > Length: 1950230 (1.9M), 305960 (299K) remaining
> >> > > [application/pdf]
> >> > > > > > > > > Saving to: `barvazi2.pdf'
> >> > > > > > > > >
> >> > > > > > > > > 100%[+++++++++++++++++++++++++++++++++++++++=======>]
> >> 1,950,230
> >> > > > > > > > > 295K/s   in 1.0s
> >> > > > > > > > >
> >> > > > > > > > > 2009-01-20 21:38:30 (295 KB/s) - `barvazi2.pdf' saved
> >> > > > > [1950230/1950230]
> >> > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > > > On Tue, Jan 20, 2009 at 9:31 PM, jeff emminger <
> >> > > > > jemminger at gmail.com>
> >> > > > > > > > > wrote:
> >> > > > > > > > > >> Could anyone confirm that this works:
> >> > > > > > > > > >> wget --limit-rate=3500
> >> > > > > > > http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > >> while this doesn't:
> >> > > > > > > > > >> wget http://www.noal.org.il/static/temp/barvazi2.pdf
> >> > > > > > > > > >>
> >> > > > > > > > > >
> >> > > > > > > > > > Confirmed
> >> > > > > > > > > >
> >> > > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > > >
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > --
> >> > > > > > > > Yo'av Moshe
> >> > > > > > >
> >> > > > > > > --
> >> > > > > > > Igor Sysoev
> >> > > > > > > http://sysoev.ru/en/
> >> > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > > >
> >> > > > > > --
> >> > > > > > Yo'av Moshe
> >> > > > >
> >> > > > > --
> >> > > > > Igor Sysoev
> >> > > > > http://sysoev.ru/en/
> >> > > > >
> >> > > > >
> >> > > >
> >> > > >
> >> > > > --
> >> > > > Yo'av Moshe
> >> > >
> >> > > --
> >> > > Igor Sysoev
> >> > > http://sysoev.ru/en/
> >> > >
> >> > >
> >> >
> >> >
> >> > --
> >> > Yo'av Moshe
> >>
> >> --
> >> Igor Sysoev
> >> http://sysoev.ru/en/
> >>
> >>
> >
> >
> > --
> > Yo'av Moshe
> >
> 
> 
> 
> -- 
> Yo'av Moshe

-- 
Igor Sysoev
http://sysoev.ru/en/

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