Optimize status.cgi

[Jonathan Kamens]

With nagios 3.2.0 at my site, it took over a minute from when I entered 
a host name in the Web UI's "Quick Search:" box and hit Enter, until 
when the status details for the host were actually displayed.

The attached patch reduces the time to do exactly the same work to under 
five seconds.

It adds the following optimizations to the code base:

   1. When iterating through the lines in the status.dat file, use a
      persistent buffer to read lines rather than freeing and
      reallocating a new buffer for every line.  This reduces
      fragmentation of the malloc pool and reduces the amount of time
      spent in malloc() and free().  This is implemented by adding a new
      function, mmap_fgets_buf(), which is like mmap_fgets() except it
      takes an optional buffer to reuse if possible.  I added this to
      both cgiutils.c and utils.c so that it can be used elsewhere in
      the code.
   2. When parsing the status.dat file, reduce the number of unnecessary
      calls to strcmp() by keeping track of when we know we're in a
      block and not checking for block-start sequences unnecessarily.
   3. Defer the sorting of the comment and scheduled downtime linked
      lists until they've all been read from status.dat.  This makes a
      */huge/* difference in performance -- it dwarfs by orders of
      magnitude the optimizations listed above.  The way this is
      implemented is invisible to programs aside from status.cgi that
      call add_comment() or add_downtime(), but those programs can
      easily be modified to take advantage of the new functionality if
      they need to be sped up.

I sincerely hope that the maintainers of Nagios will make an effort to 
include these changes in the next release.  They represent a dramatic 
improvement in the performance and usability of the Web UI.

Thanks,

Jonathan Kamens

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