Update and clarify replication docs

doc/guide/admin/replication.sdf

@@ -347,6 +347,10 @@ is too far out of sync (or completely empty), conventional syncrepl is used to
 bring it up to date and replication then switches back to the delta-syncrepl
 mode.
 
+Note: partial replication is incompatible with deltasync. For deltasync to
+work, the replication user needs unrestricted read access to both the main
+database and accesslog database.
+
 Note: since the database state is stored in both the changelog DB and the
 main DB on the provider, it is important to backup/restore both the changelog
 DB and the main DB using slapcat/slapadd when restoring a DB or copying
@@ -481,9 +485,18 @@ The provider is implemented as an overlay, so the overlay itself
 must first be configured in {{slapd.conf}}(5) before it can be
 used. The provider has two primary configuration directives and
 two secondary directives for when delta-syncrepl is being used.
+
 Because the LDAP Sync search is subject to access control, proper
 access control privileges should be set up for the replicated
-content.
+content. In many environments the replicas are meant to carry the
+same data as provider so the replication user needs unrestricted
+read access to the database and as such this tends to be the first
+access rule for that database:
+
+> access to * by "$REPLICATOR" read by * break
+
+However if partial replication is desired, the access rules can be
+tightened appropriately.
 
 The two primary options to configure are the checkpoint and
 sessionlog behaviors.
@@ -497,7 +510,13 @@ operations. If {{<ops>}} operations or more than {{<minutes>}}
 time has passed since the last checkpoint, a new checkpoint is
 performed. Checkpointing is disabled by default.
 
-The session log is configured by the
+If an accesslog is maintained for this database and contains all the
+successful writes, it is the preferred way to provide the resync
+information:
+
+> syncprov-sessionlog-source <accesslog db suffix>
+
+Otherwise an in memory session session log is configured by the
 
 >	syncprov-sessionlog <ops>
 
@@ -535,7 +554,7 @@ A more complete example of the {{slapd.conf}}(5) content is thus:
 >
 >	overlay syncprov
 >	syncprov-checkpoint 100 10
->	syncprov-sessionlog 100
+>	syncprov-sessionlog-source cn=accesslog
 
 
 H4: Set up the consumer slapd