yes,
please simone put it in the jboss.xml howto and/or a separate howto
marc
|-----Original Message-----
|From: [EMAIL PROTECTED]
|[mailto:[EMAIL PROTECTED]]On Behalf Of Hayden, Ty
|Sent: Thursday, October 26, 2000 7:23 AM
|To: 'jBoss'
|Subject: RE: [jBoss-User] Advanced Cache Settings explanation
|
|
|
|Thank you Simone - Good Job.
|
|I could have used this yesterday... We need to place this in the Advanced
|JBoss Configuration section of the manual. :->
|
|Thanks,
|
|Ty
|
|
|
|-----Original Message-----
|From: Bordet, Simone [mailto:[EMAIL PROTECTED]]
|Sent: Thursday, October 26, 2000 5:06 AM
|To: jBoss Development Mailing List (E-mail); jBoss User Mailing List
|(E-mail)
|Subject: [jBoss-User] Advanced Cache Settings explanation
|
|
|Hello all,
|
|I'd like to state that I really have no experience on what are the best
|default values for the cache parameters, so everyone may
|contribute and post
|his/her experience on tuning these parameters.
|
|Here's the explanation for the jboss.xml tags regarding the caches.
|
|<cache-policy>org.jboss.ejb.plugins.LRUEnterpriseContextCachePolicy
|</cache-p
|olicy>
|
|This tag specifies the cache policy you want to use; actually 2 are
|implemented, the above one and
|org.jboss.ejb.plugins.NoPassivationCachePolicy. This tag is mandatory, ie
|must always exist and be non empty.
|
|Now the cache policy configuration. The following tags are not
|mandatory and
|should have a default from standardjboss.xml if you don't specify them in
|your jboss.xml.
|
|NoPassivationCachePolicy doesn't have any configuration, so the
|cache-policy-conf tag makes no sense for it.
|LRUEnterpriseContextCachePolicy can be configurated.
|
|<cache-policy-conf>
|
|The tag that specify advanced settings.
|
| <min-capacity>5</min-capacity>
|
|This is the minimum *capacity* of the cache. The cache can be empty, but
|will have room for at least 5 beans (in this case); this value cannot be
|less than 2; the resizer (see below) will shrink the cache capacity down to
|but not less than this value.
|
| <max-capacity>200</max-capacity>
|
|This is the maximum *capacity* of the cache. The cache can be empty, but
|will have room for at most 200 beans (in this case); this value cannot be
|less than the minimum capacity; the resizer (see below) will enlarge the
|cache capacity up to but not more than this value.
|
| <overager-period>600</overager-period>
|
|The overager is a periodic task that runs (in this case) every 600 seconds.
|Purpose of this periodic task is to see if in the cache there are very old
|beans, and to passivate them. The age at which a bean is considered too old
|is also configurable (see below). While the period of this task is 600
|seconds, the *first run* happens at a random time between 0 and 600 seconds
|(in this case).
|
| <resizer-period>600</resizer-period>
|
|The resizer is a periodic task that runs (in this case) every 600 seconds.
|Purpose of this periodic task is to shrink / enlarge the cache *capacity*
|upon 3 parameters (see below). While the period of this task is
|600 seconds,
|the *first run* happens at a random time between 0 and 600 seconds (in this
|case).
|
|
| <max-bean-age>600</max-bean-age>
|
|This is the max age a bean can have before being passivated by the overager
|(in this case 600 seconds). See the overager above.
|
| <max-cache-miss-period>60</max-cache-miss-period>
| <min-cache-miss-period>1</min-cache-miss-period>
| <cache-load-factor>0.75</cache-load-factor>
|
|These 3 parameters control the resizer in this way: the number of cache
|misses is internally recorded. When the resizer runs, it sees what is the
|cache miss rate from the last time it ran. If there is more than (in this
|case) one cache miss every 1 second (min-cache-miss-period) then
|the resizer
|tries to enlarge the cache; if there is less than (in this case) one cache
|miss every 60 seconds (max-cache-miss-period) then the resizer tries to
|shrink the cache.
|How much is the cache enlarged / shrinked ? Here is where the load factor
|comes in the picture. When the resizer shrinks, it tries to shrink
|the cache
|so that (in this case) the ratio number of beans / cache capacity is 0.75;
|when the resizer enlarges, it tries to enlarge the cache by a factor 1 /
|0.75 == 1.333 (in this case) plus a correction calculated from the cache
|miss rate (ie the more cache miss rate you have, the more the cache is
|enlarged, starting from at least 1.333; so if you really have a
|lot of cache
|misses, the resizer may decide to enlarge the cache of a factor 2.0 instead
|of 1.333 - if there is room for that).
|
|Bye
|
|Simon
|
|
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