(ITS#7609) back-meta enhancement: filter patterns for target selection

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: 2.4.35
OS: 
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (78.155.233.73)
Submitted by: hyc


Since a lot of applications perform DN lookups using a search filter, it would
be useful to allow specifying a regex pattern match on filters to select a
target.
This would avoid broadcasting a suffix-level search to all targets
unnecessarily.

The intended use case is for a system where the DIT is sharded across multiple
servers, and entries are distributed across each target using some regular
pattern.
(e.g., uid=a.* on target1, uid=b.* on target2, etc...)