Recommended setup with large cache memory

[Brad Knowles]

At 11:31 AM +0200 2005-09-09, Attila Nagy wrote:

>  That depends. I didn't look the source, but if it walks through the
>  entries every time to get the expired ones out, doing cleaning more
>  often on a large dataset will be slower.

	No.  Experience has shown that cleaning more often results in 
each cleaning session taking less time.

>  BTW, it seems that the cleaning takes about the same time, even in the
>  very early morning, when the load is about 4-5 lower than in the daytime
>  peak.
>  So I guess the needed time is based on the number of cached entries and
>  not on the number of expired entries.

	You can't gauge the amount of expired entries based on the query 
load.  You could only know that based on actually stepping through 
the cached data and looking to see what is there.  My experience is 
that the number of expired entries is more closely related to the 
total number of entries overall, than anything to do with query load 
by the hour.

>  We have many nameservers, it is just embarassing to do cleaning on them.
>  And getting each one out of the pool just for this is insane.

	Which is another reason why Kevin's request is a good one -- put 
load-balancing switches in front of the caching servers, then take 
the machines out of the switch pool when you go to do the cleaning, 
and put them back in the pool when you're done.

	I think he's hit on exactly the right idea here.

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.