> So afaik the current 2.4 behavior is to enforce the minimum number of spare
> threads as
>
> ThreadsPerChild * num_buckets
>
> with num_buckets equal 1 if you are not leveraging SO_REUSEPORT
> (https://httpd.apache.org/docs/current/mod/mpm_common.html#listencoresbucketsratio).
> This means that if you have only > one busy thread the minimum number of
> httpd processes running will be always two. The new threshold is the more
> conservative:
>
> ThreadsPerChild * (num_buckets - 1) + num_buckets
>
> In your case, with num_buckets = 1, the lower bound of min spare threads is
> one, enabling the possibility to get down to only one httpd process (because
> the MinSpareThread lower bound won't > mess with your Min/MaxSpareThread
> settings anymore).
>
> More info in Yann's explanation:
> http://svn.apache.org/viewvc?view=revision&revision=1737447
>
> Let me know if it makes sense! If so, to fix your problem you'd need to apply
> the patch to the httpd source and recompile or wait for the backport to be
> reviewed/merged into the 2.4.x branch (and released afterwards).
>
> Luca
Sorry for the delay. My updated packages were installed over the weekend, and
this does appear to fix the issue with me for the normal num_buckets = 1 case
(all I use).
I'm far from an expert on the feature here, but wouldn't this behavior with
num_buckets > 1 still leave the workload unbalanced? I thought the point per
Yann's comment ("We want the number of children processes to be a multiple of
the number of buckets so to optimally accept connections") was to balance the
processes even between the listeners? I get that the initial startup case is
fine, but in the case of num_buckets = 2, if thread usage gets to > 50%, this
would seem to spawn a third, potentially unwanted process, leaving the workers
unbalanced when the load really shouldn't be. I would have thought the way
forward is leaving the idle thread minimum alone, forcing StartServers >=
num_buckets, and enforcing a minimum process count = num_buckets. If process
counts should be multiples of num_buckets, scaling any process count
expands/shrinks by num_buckets would seem to be the way to accomplish this. I
think this would also need a check to ensure that MaxSpareThreads >=
MinSpareThreads + num_buckets * ThreadsPerChild + num_buckets.
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