Re: [naviserver-devel] ns_cache

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

Yes, dynamic caches are very useful, i checked my code and i use them as 
well

Zoran Vasiljevic wrote:
> 
> Am 22.10.2005 um 15:51 schrieb Stephen Deasey:
> 
>> On 10/22/05, Zoran Vasiljevic <zv...@ar...> wrote:
>>
>>>
>>> Am 21.10.2005 um 15:19 schrieb Vlad Seryakov:
>>>
>>>
>>>> Looks okay, API has changed but if we accept it, i suppose onetime
>>>> code change is acceptable
>>>>
>>>>
>>>
>>> What about timed cache? I miss this (for us) important feature.
>>>
>>
>>
>> The existing implementation doesn't make a lot of sense to me.  You
>> can create either a size limited cache, OR a time based cache.  A time
>> based cache has it's entries flushed based on the mtime, i.e. only
>> when they're unused.  This means popular entries will never be
>> flushed.
>>
>> What you really want is for entries to have a max cache lifetime (ADP
>> pages), possibly different for each entry (DNS lookups).
> 
> 
> 
> OK. This is true, indded.
> 
> 
>>
>>
>>
>>> Why passing the cacheTable over ClientData?
>>>
>>
>>
>> That's just because I implemented this as a module so it could be
>> tested easily without patching.  A merged version would add a slot to
>> the NsServer structure.
> 
> 
> OK. This is clear.
> 
>>
>>
>>
>>> Why not creating caches during server lifetime instead of only
>>> at startup?
>>>
>>
>>
>> Locking overhead.  The current implementation doesn't lock the caches
>> when for example the stats command is run, which could have the cache
>> deleted out from under it, causing a crash.
>>
>> I did try a couple of ways to enable safe cache creation at runtime,
>> including reference counting of the caches themselves.  It just seemed
>> over engineered.
>>
>> Do you have a situation in mind where caches should be created at  
>> runtime?
> 
> 
> Oh yes... We have a database lib (Codebase) which is fast, but some  of the
> things we did there take time. Hence, I use the cache module to keep  those
> difficult computations in a timed-cache. Now, I have attached a cache to
> each opened database. The databases can be opened for read/write  
> (single writer
> multiple readers) by any thread during the runtime. I do not want to  open
> all those db's on the filesystem. For example, our backup index may  
> consists
> of 100's of tiny databases. I can't just open them all at startup.
> Oh yes: a database is just a handful of files: datafile, index file,  
> blob file.
> 
> Hm... to be ultimately useful, it would need to be dynamic, I'm afraid.
> 
> OTOH, you need not make it 100% dynamic. You can just create caches, but
> never destroy them, for example. In our app, the name of the cache is
> bound to a file-name (i.e. directory where db files live). This does not
> change over lifetime.
> 
> 
> Cheers
> Zoran
> 
> 
> 
> -------------------------------------------------------
> This SF.Net email is sponsored by:
> Power Architecture Resource Center: Free content, downloads, discussions,
> and more. http://solutions.newsforge.com/ibmarch.tmpl
> _______________________________________________
> naviserver-devel mailing list
> nav...@li...
> https://lists.sourceforge.net/lists/listinfo/naviserver-devel

-- 
Vlad Seryakov
571 262-8608 office
vl...@cr...
http://www.crystalballinc.com/vlad/