After running SLAMD against back-ldap I've noticed some problems in the approach - while a single load generator may send multiple requests over a single connection, back-ldap always creates new connections for each incoming Simple Bind, and leaves them available to be shared by other sessions.
We cured this by forcing back-ldap to always use idassert: this way, binds are done with dedicated (serialized) "privileged" connections pool, and the rest goes into the usual privileged connections pool.
Thinking about it, this usage doesn't really make a lot of sense. Any identity that's explicitly binding to back-ldap is necessarily going to be different from any other session's ID. The only sessions that it makes sense to share are those that were implicitly bound because they were authenticated elsewhere, and fell into this backend (via glue, typically) while processing some other request.
So I think this means we should separate out the explicitly bound connections from everything else. They should only live as long as their inbound slapd connection lives, and should only be used by ops from their inbound slapd connection.
I think that's how it is right now: implicit binds go into the lists of privileged connections, while the AVL holds only connections resulting from explicitly bound requests. What's treated separately right now, and needs to be so, is connections for explicit binds: they shouldn't get into the AVL at all until the bind succeeds (see ITS#5154 wrt/ back-meta).
One thing that probably should default to "on" is single-conn: this feature forces back-ldap to uncache connections when rebinding. In fact, the usual behavior only makes sense when a client plans to repeatedly bind on one connection with different identities, and do something with those identities. In this case, if the client at some point needs to re-use an identity that was used earlier, the connection will already be available. With single-conn on, as soon as a client rebinds on an existing connection, the old one is removed.
A totally different approach, but probably not worth except when the number of identities is guaranteed to be small, consists in caching connections based on the identity only. In that case, multiple clients binding with the same connection could re-use the same connection. This approach could be used by extending the concept of "privileged connection" to a set of limited, well-known privileged users.
p.
Ing. Pierangelo Masarati OpenLDAP Core Team
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