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Re: MTR related community contribution



IIUC one of limitations might be caused by mtr reserving 20 TCP ports per
instance, first reserved port is 16000. This leaves (65535 - 16000) / 20= 2476.75
max possible mysqld instances.


On Sun, Feb 07, 2016 at 12:52:01PM +0100, Vladislav Vaintroub wrote:
> On 2/6/2016 1:02 PM, Vicențiu Ciorbaru wrote:
> >Hi Vlad,
> >
> >I'm looking at the community pull request https://github.com/grooverdan/mariadb-server/commit/a9dfee63bad7393002621f92c15f1debd535ee1a
> >
> >I have a question regarding your commit:
> >2943d2b7e99b4221ef481890fc9a56ad569f3985
> >
> >The contribution aims to remove the hard limit of 50 unique ids as it
> >seems to cause problems for some use cases with a lot of proceeses. It
> >does this by either leaving it at 50 or to be equal to the number of
> >spawned processes.
> >
> >I'm thinking that even setting the limit of unique ids to num_processes
> >might cause problems if there is another mtr running in parallel and both
> >have > 50 processes. This is probably minor but why set this limit so low?
> >Wouldn't a larger number (say 10k) be ok? Or why not generate a random
> >number and lock a file with that number? (if the random number is invalid,
> >generate a new one. On average it should finish quite quickly)
> Hi Vicentiu,
> The 50 ports range limit was there before my patch, I  just moved the start
> of the the range up from 250 to 300, so that the old mtr and "new"(i.e new
> in 2008) mtr have non-overlapping port range- because these 2 mtrs have
> different  conflicting ideas of when a port is free.
> 10K or so limit should be fine. The reason why the limit is so small is
> unknown to me. Perhaps back in the day 50 mysqlds on the same machine were
> considered ought to be enough for anybody:)
> I'm not sure randomization needs  implementing, unless a measurement would
> show that it takes noticeable amount of time during startup.  Randomization
> could be  a minor annoyance to some people if they are used to have
> particular port numbers when mysqld is started via mtr, so if it does not
> bring much , maybe better not to do it.
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