503 responses with "backend write error: 11"

[Carlos Valiente]

Hi! I'm running varnish 2.1.13 on OpenSuSE 11.1 64-bit. From time to
time I'm seeing these kind of errors:

   22 ReqStart     c 10.0.0.1 2396 1481986113
   22 RxRequest    c POST
   22 RxURL        c /backend/statistics/
   22 RxProtocol   c HTTP/1.1
   22 RxHeader     c Host: www.example.com
   22 RxHeader     c User-Agent: Mozilla/5.0 (Windows; U; Windows NT
5.1; en-GB; rv:1.9.2.4) Gecko/20100527 Firefox/3.6.4
   22 RxHeader     c Accept: application/json, text/javascript, */*
   22 RxHeader     c Accept-Language: en-gb,en;q=0.5
   22 RxHeader     c Accept-Encoding: gzip,deflate
   22 RxHeader     c Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
   22 RxHeader     c Keep-Alive: 115
   22 RxHeader     c Connection: keep-alive
   22 RxHeader     c Content-Type: application/x-www-form-urlencoded;
charset=UTF-8
   22 RxHeader     c X-Requested-With: XMLHttpRequest
   22 RxHeader     c Referer: http://www.example.com/foo/
   22 RxHeader     c Content-Length: 29847
   22 RxHeader     c Cookie: foo=bar
   22 RxHeader     c Pragma: no-cache
   22 RxHeader     c Cache-Control: no-cache
   22 VCL_call     c recv
   22 VCL_return   c pass
   22 VCL_call     c hash
   22 VCL_return   c hash
   22 VCL_call     c pass
   22 VCL_return   c pass
   22 Backend      c 20 default backend3
   22 Backend      c 20 default backend3
   22 FetchError   c backend write error: 11
   22 VCL_call     c error
   22 VCL_return   c deliver
   22 VCL_call     c deliver
   22 VCL_return   c deliver
   22 TxProtocol   c HTTP/1.1
   22 TxStatus     c 503
   22 TxResponse   c Service Unavailable
   22 TxHeader     c Server: Varnish
   22 TxHeader     c Retry-After: 0
   22 TxHeader     c Content-Type: text/html; charset=utf-8
   22 TxHeader     c Content-Length: 419
   22 TxHeader     c Date: Tue, 16 Nov 2010 15:00:01 GMT
   22 TxHeader     c X-Varnish: 1481986113
   22 TxHeader     c Age: 5
   22 TxHeader     c Via: 1.1 varnish
   22 TxHeader     c Connection: close
   22 TxHeader     c X-Cache: MISS
   22 Length       c 419
   22 ReqEnd       c 1481986113 1289919596.007149696
1289919601.033036232 0.000028849 5.025856972 0.000029564
   22 SessionClose c error
   22 StatSess     c 10.0.0.1 2396 5 1 1 0 1 0 250 419

I have a couple of questions regarding this issue:

  1. It seems to me that Varnish fails when it tries to *write* the
request to the backend -- is this correct?

  2. The integer value '11' reported in "backend write error: 11" --
is it the value of ``errno`` for the failed call to ``write(2)``?

  3. If [2] above is correct: In the platform where Varnish is
running, 11 seems to correspond to EAGAIN:

        $ python -c 'import errno; print errno.EAGAIN'
        11
        $

     Is there any way of telling Varnish to try the write(2) again?

Cheers,

Carlos