Re: [naviserver-devel] read/write ns_config

[Vlad S. <vl...@cr...>]

Then we can just go through the code(fastpath, log) and change it so it 
copies config at startup into local variables (as in server.c) if that 
particular code does not care about realtime changes. This way it will 
be a compromise between locking and performance.

Zoran Vasiljevic wrote:
> On 23.08.2006, at 16:17, Vlad Seryakov wrote:
> 
>> Looking thru the code i see that mostly only fastpath and log uses
>> NsConfig reads in real time, all others are copy values into local
>> structures. funny, but these who uses config are performance critical
>> and will introduce lock contention because thet are figthing for the
>> same config values.
>>
>> Another raw/uncooked idea: is it possible to keep changed values
>> separately, no lock default config as is now and whoever changed value
>> just keep it in the lock-guarded hash. If i care about locking and
>> changed value i will check new hash for new value, others who does not
>> may still use read-only config list.
> 
> I do not know how this could work. If thread A changes
>    ns/some/thing
> and thread B is constantly looking up the
>    ns/some/thing
> then the B must always lock to get the value, as A may
> be fiddling with it at the same time.
> 
> Thread B can of course copy the value in its
> private (tsd) copy on the first fetch but
> then again, HOW is he going to find out that the
> thing was changed by the A in the meantime?
> 
> I do not believe you can avoid locking if you want
> to have consistent behaviour.
> 
> Also, the changes done by thread A would be pretty
> meaningless if only A is able to see them...
> I do not believe this is worth examining.
> 
> As said, locking cannot be avoided. It is just the question
> of: can we tolerate it or not? I can. Therefore for me it
> is irelevant. But I do not if you can. Therefore I'm looking
> to see if we can do this as runtime or compile-time option.
> Also, because the locking is needed, we have to see how we
> can minimize it, also minimizing time spent in the locked
> sections of the code (by speeding up certain operations for
> example).
> 
> Cheers
> Zoran
> 
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-- 
Vlad Seryakov
571 262-8608 office
vl...@cr...
http://www.crystalballinc.com/vlad/