Directives in this category only apply a BDB database. That is, they must follow a "database bdb" line and come before any subsequent "backend" or "database" line. For a complete reference of BDB configuration directives, see the slapd-bdb manpages (man slapd-bdb).
This directive specifies the directory where the BDB files containing the database and associated indexes reside.
sessionlog <sid> <limit>
This directive specifies a session log store in the syncrepl replication provider server which contains information on the entries that have been scoped out of the replication content identified by <sid>. The first syncrepl search request having the same <sid> value in the cookie establishes the session log store in the provider server. The number of the entries in the session log store is limited by <limit>. Excessive entries are removed from the store in the FIFO order. Both <sid> and <limit> are non-negative integers. <sid> has no more than three decimal digits.
The LDAP Content Synchronization operation that falls into a pre-existing session can use the session log store in order to reduce the amount of synchronization traffic. If the replica is not so outdated that it can be made up-to-date by the information in the session store, the provider slapd will send the consumer slapd the identities of the scoped-out entries together with the in-scope entries added to or modified within the replication content. If the replica status is outdated too much and beyond the coverage of the history store, then the provider slapd will send the identities of the unchanged in-scope entries along with the changed in-scope entries. The consumer slapd will then remove those entries in the replica which are not identified as present in the provider content.
For more informations about syncrepl, please visit : LDAP Sync Replication.