Performance drop considerably when Alias is enabled

The problem

We found that when an application is associated to an LDAP directory and aliasing is enabled, performance drops considerably.

Diagnose

This can be observed executing the following command:

time curl -u <application_name>:<application_password> -v http://localhost:8095/crowd/rest/usermanagement/1/search?entity-type=user > output.txt

This problem is aggravated in large user bases, but it's possible to replicate with just a small set of users (less than 100):

• Alias disabled:

  real	0m0.121s
  user	0m0.004s
  sys	0m0.003s
  

• Alias enabled:

  real	0m0.514s
  user	0m0.004s
  sys	0m0.003s
  

Turning com.atlassian.crowd into DEBUG and enabling profiling a massive number of messages referring to AliasManager.findAliasByUsername() appears on atlassian-crowd.log.

Apparently it was an issue in previous versions (CWD-2054), it may be a recurrence.