Theuser-dened table to use for validation when the validation method is table. Defaults
totest.
Ifthis method is used, the table used should be dedicated only to validation, and the number
ofrows in the table should be kept to a minimum.
■FailAll Connections
Indicateswhether all connections in the pool are re-created when one is found to be invalid,
oronly the invalid one. Only applicable if you have selected a connection validation method.
Disabledby default.
Ifenabled, all of the re-creation is done in one step, and the thread requesting the
connectionis heavily aected. If disabled, the load of re-creating connections is distributed
betweenthe threads requesting each connection.
■TransactionIsolation Level
Speciesthe Transaction Isolation Level on the pooled database connections.
Bydefault, the default isolation level of the connection is left intact. Setting it to any value
doesincur the small performance penalty caused by the method call.
■GuaranteeIsolation
Onlyapplicable if a transaction isolation level is specied. Defaults to disabled.
Leavingthis setting disabled causes the isolation level to be set only when the connection is
created.Enabling sets the level every time the connection is leased to an application. In most
cases,leave this setting disabled.
Tuningthe ACL User Cache
TheACL user cache is on by default. Because of the default size of the cache (200 entries), the
ACLuser cache can be a bottleneck, or can simply not serve its purpose on a site with heavy
trac.On a busy site, more than 200 users can hit ACL-protected resources in less time than the
lifetimeof the cache entries. When this situation occurs, Web Server must query the LDAP
servermore often to validate users, which impacts performance.
Thisbottleneck can be avoided by increasing the maximum users of the ACL cache on the
conguration'sPerformance tab ⇒Cache sub tab. You can also set the number of users by
settingthe max-users property using the command wadm set-acl-cache-prop. Note that
increasingthe cache size uses more resources; the larger you make the cache, the more RAM
you'llneed to hold it.
Therecan also be a potential (but much harder to hit) bottleneck with the number of groups
storedin a cache entry (four by default). If a user belongs to ve groups and hits ve ACLs that
checkfor these dierent groups within the ACL cache lifetime, an additional cache entry is
createdto hold the additional group entry. When there are two cache entries, the entry with the
originalgroup information is ignored.
TuningtheACL User Cache
Chapter2 • Tuning Sun Java System Web Server 77