addpartial Overlay README

DESCRIPTION
    This package contains an OpenLDAP overlay called "addpartial" that 
    intercepts add requests, determines if the entry exists, determines what 
    attributes, if any, have changed, and modifies those attributes.  If the
    entry does not exist, the add request falls through and proceeds normally.
    If the entry exists but no changes have been detected, the client receives
    LDAP_SUCCESS (I suppose it is debatable what to do in this case, but this is
    the most clean for my use.  The LDAP_SUCCESS lets me know that the entry I
    sent slapd == the entry already in my slapd DB.  Perhaps this behavior
    should be configurable in the future).

    When a change is found, the addpartial overlay will replace all values for
    the attribute (if an attribute does not exist in the new entry but exists
    in the entry in the slapd DB, a replace will be done with an empty list of
    values).

    Once a modify takes place, the syncprov overlay will properly process the
    change, provided that addpartial is the first overlay to run.  Please see
    the CAVEATS for more specifics about this.

    The addpartial overlay makes it easy to replicate full entries to a slapd 
    instance without worrying about the differences between entries or even if
    the entry exists.  Using ldapadd to add entries, the addpartial overlay can
    compare about 500 records per second.  The intent of the addpartial overlay
    is to make it easy to replicate records from a source that is not an LDAP
    instance, such as a database.  The overlay is also useful in places where it
    is easier to create full entries rather than comparing an entry with an
    entry that must be retrieved (with ldapsearch or similar) from an existing
    slapd DB to find changes. 

    The addpartial overlay has been used in production since August 2004 and has
    processed millions of records without incident.

BUILDING
    A Makefile is included, please set your OPENLDAP_SRC directory properly.

INSTALLATION
    After compiling the addpartial overlay, add the following to your 
    slapd.conf:

    ### slapd.conf
    ...
    moduleload /path/to/addpartial-overlay.so
    ...
    # after database directive...
    # this overlay should be the last overlay in the config file to ensure that
    # it properly intercepts the add request
    overlay addpartial
    ...
    ### end slapd.conf

CAVEATS
    - In order to ensure that addpartial does what it needs to do, it should be
      the last overlay configured so it will run before the other overlays.
      This is especially important if you are using syncrepl, as the modify that
      addpartial does will muck with the locking that takes place in the
      syncprov overlay.
