Re: (ITS#4888) Enhance back-sql with paged results

[hyc@symas.com]

adamson@cmu.edu wrote:
> Full_Name: Mark Adamson
> Version: HEAD
> OS: Solaris 2.8
> URL: http://null.andrew.cmu.edu/openldap/sql_paged_results.patch
> Submission from: (NULL) (128.2.234.24)
> 
> 
> Here at Carnegie Mellon we had a need to use the LDAP_CONTROL_PAGEDRESULTS
> control with the SQL backend. The patch to add this is not hard, and was mostly
> copied from the back-bdb/search.c file.
> 
> http://null.andrew.cmu.edu/openldap/sql_paged_results.patch
> 
> The only challenge was the contents of the cookie that is used to maintain
> state. The slap.h file defines the PagedResultsCookie type to be an unsigned
> long, so I wanted to fit everything into that. The design idea was to keep the
> ldap_entries.id value of the last returned entry in the cookie so that
> subsequent searches could add a "AND ldap_entries.id > COOKIEVALUE" clause to
> the SQL query. However, the gathering of candidate entries is done across all
> objectClasses with avl_apply(), so if one OC returns an entry with a high
> ldap_entries.id, objectClasses that come later in the AVL could miss entries.
>   For this reason, I add the oc_map_id of the last returned entry to the cookie,
> and I adjusted the avl_apply() call to run through the objectClasses in numeric
> order. In this way, when subsequent pages of entries are requested, all of the
> objectClasses that were completed by previous pages can be skipped for the new
> page. When we get to the objectClass where the previous page left off, we take
> the ldap_entries.id from the cookie and apply the above mentioned SQL clause.

A more appropriate change would probably be to change the cookie type to 
a berval so that arbitrary data may be used as needed by each backend. 
Then you can set both the oc_map_id and the ldap_entries.id.

Ultimately this sort of thing should be handled almost entirely by the 
frontend, with just a single call in the backend to fill a cookie struct 
for the current search state.
-- 
   -- Howard Chu
   Chief Architect, Symas Corp.  http://www.symas.com
   Director, Highland Sun        http://highlandsun.com/hyc
   Chief Architect, OpenLDAP     http://www.openldap.org/project/