Optimize status.cgi

[Ton Voon]

Hi Jonathan,

Just to let you know that I'll look into this soon. I have had reports  
that lots of downtime causes a CGI slowdown, and it looks like you've  
nailed where it is. Did you use any particular tools to identify this?

I'll probably get (3) added in first and defer (1) and (2) for later  
versions.

BTW, it will be useful to have multiple patches, so can apply them one  
at a time, rather than a single large patch.

Ton

On 23 Dec 2009, at 02:26, Jonathan Kamens wrote:

> 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:
> 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.
> 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.
> 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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