When does a session close with a "blast"?

Cosimo Streppone cosimo at streppone.it
Wed Mar 31 18:20:38 CEST 2010

We're running varnish 2.0.4 on some moderately busy
servers, ~1200 req/s peak.

Today I was looking at the output of:

   varnishtop -i SessionClose

which is very interesting BTW, when I noticed
that a new value was suddenly added to the list,
that looked like this, more or less:

   7557.34 SessionClose   timeout
    901.28 SessionClose   no request
    753.54 SessionClose   remote closed
    317.48 SessionClose   error
     73.18 SessionClose   Connection: close
     60.32 SessionClose   overflow
     20.81 SessionClose   not HTTP/1.1
      0.05 SessionClose   blast         <--- HERE!

So, questions:

1) Does this distribution look "normal"?
    These servers have a sess_timeout of 2s, and they are serving
    a large (tens of millions) set of medium to large files.

2) What does "blast" mean for a SessionClose?
    Reading the source code for 2.0.4, it would seem to me that
    "blast" originates from overflowing sess_workspace.
    If this is correct, would a simple increase of sess_workspace prevent

    And yes, I'm assuming a blast is a bad thing. :)



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