# $OpenLDAP$
# Copyright 2007-2020 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.

H1: Changes Since Previous Release

The following sections attempt to summarize the new features and changes in OpenLDAP
software since the 2.3.x release and the OpenLDAP Admin Guide.

H2: New Guide Sections

In order to make the Admin Guide more thorough and cover the majority of questions
asked on the OpenLDAP mailing lists and scenarios discussed there, we have added the following new sections:

* {{SECT:When should I use LDAP?}}
* {{SECT:When should I not use LDAP?}}
* {{SECT:LDAP vs RDBMS}}
* {{SECT:Access Control}}
* {{SECT:Backends}}
* {{SECT:Overlays}}
* {{SECT:Replication}}
* {{SECT:Maintenance}}
* {{SECT:Monitoring}}
* {{SECT:Tuning}}
* {{SECT:Troubleshooting}}
* {{SECT:Changes Since Previous Release}}
* {{SECT:Upgrading from 2.3.x}}
* {{SECT:Common errors encountered when using OpenLDAP Software}}
* {{SECT:Recommended OpenLDAP Software Dependency Versions}}
* {{SECT:Real World OpenLDAP Deployments and Examples}}
* {{SECT:OpenLDAP Software Contributions}}
* {{SECT:Configuration File Examples}}
* {{SECT:LDAP Result Codes}}
* {{SECT:Glossary}}

Also, the table of contents is now 3 levels deep to ease navigation.


H2: New Features and Enhancements in 2.4

H3: Better {{B:cn=config}} functionality

There is a new slapd-config(5) manpage for the {{B:cn=config}} backend. The 
original design called for auto-renaming of config entries when you insert or 
delete entries with ordered names, but that was not implemented in 2.3. It is 
now in 2.4. This means, e.g., if you have

>   olcDatabase={1}mdb,cn=config
>   olcSuffix: dc=example,dc=com

and you want to add a new subordinate, now you can ldapadd:

>   olcDatabase={1}mdb,cn=config
>   olcSuffix: dc=foo,dc=example,dc=com

This will insert a new back-mdb database in slot 1 and bump all following databases
 down one, so the original back-mdb database will now be named:

>   olcDatabase={2}mdb,cn=config
>   olcSuffix: dc=example,dc=com

H3: Better {{B:cn=schema}} functionality

In 2.3 you were only able to add new schema elements, not delete or modify 
existing elements. In 2.4 you can modify schema at will. (Except for the 
hardcoded system schema, of course.)

H3: More sophisticated Syncrepl configurations

The original implementation of Syncrepl in OpenLDAP 2.2 was intended to support 
multiple consumers within the same database, but that feature never worked and 
was removed from OpenLDAP 2.3; you could only configure a single consumer in 
any database.

In 2.4 you can configure multiple consumers in a single database. The configuration 
possibilities here are quite complex and numerous. You can configure consumers 
over arbitrary subtrees of a database (disjoint or overlapping). Any portion 
of the database may in turn be provided to other consumers using the Syncprov 
overlay. The Syncprov overlay works with any number of consumers over a single 
database or over arbitrarily many glued databases.

H3: N-Way Multimaster Replication

As a consequence of the work to support multiple consumer contexts, the syncrepl 
system now supports full N-Way multimaster replication with entry-level conflict 
resolution. There are some important constraints, of course: In order to maintain 
consistent results across all servers, you must maintain tightly synchronized 
clocks across all participating servers (e.g., you must use NTP on all servers). 

The entryCSNs used for replication now record timestamps with microsecond resolution, 
instead of just seconds. The delta-syncrepl code has not been updated to support 
multimaster usage yet, that will come later in the 2.4 cycle.

H3: Replicating {{slapd}} Configuration (syncrepl and {{B:cn=config}})

Syncrepl was explicitly disabled on cn=config in 2.3. It is now fully supported 
in 2.4; you can use syncrepl to replicate an entire server configuration from 
one server to arbitrarily many other servers. It's possible to clone an entire 
running slapd using just a small (less than 10 lines) seed configuration, or 
you can just replicate the schema subtrees, etc. Tests 049 and 050 in the test 
suite provide working examples of these capabilities.


H3: Push-Mode Replication

In 2.3 you could configure syncrepl as a full push-mode replicator by using it 
in conjunction with a back-ldap pointed at the target server. But because the 
back-ldap database needs to have a suffix corresponding to the target's suffix, 
you could only configure one instance per slapd.

In 2.4 you can define a database to be "hidden", which means that its suffix is 
ignored when checking for name collisions, and the database will never be used 
to answer requests received by the frontend. Using this "hidden" database feature 
allows you to configure multiple databases with the same suffix, allowing you to 
set up multiple back-ldap instances for pushing replication of a single database 
to multiple targets. There may be other uses for hidden databases as well (e.g., 
using a syncrepl consumer to maintain a *local* mirror of a database on a separate filesystem).


H3: More extensive TLS configuration control

In 2.3, the TLS configuration in slapd was only used by the slapd listeners. For 
outbound connections used by e.g. back-ldap or syncrepl their TLS parameters came 
from the system's ldap.conf file.

In 2.4 all of these sessions inherit their settings from the main slapd configuration, 
but settings can be individually overridden on a per-config-item basis. This is 
particularly helpful if you use certificate-based authentication and need to use a 
different client certificate for different destinations.


H3: Performance enhancements

Too many to list. Some notable changes - ldapadd used to be a couple of orders 
of magnitude slower than "slapadd -q". It's now at worst only about half the 
speed of slapadd -q. Some comparisons of all the 2.x OpenLDAP releases are available 
at {{URL:http://www.openldap.org/pub/hyc/scale2007.pdf}}

That compared 2.0.27, 2.1.30, 2.2.30, 2.3.33, and CVS HEAD). Toward the latter end 
of the "Cached Search Performance" chart it gets hard to see the difference 
because the run times are so small, but the new code is about 25% faster than 2.3, 
which was about 20% faster than 2.2, which was about 100% faster than 2.1, which 
was about 100% faster than 2.0, in that particular search scenario. That test 
basically searched a 1.3GB DB of 380836 entries (all in the slapd entry cache) 
in under 1 second. i.e., on a 2.4GHz CPU with DDR400 ECC/Registered RAM we can 
search over 500 thousand entries per second. The search was on an unindexed 
attribute using a filter that would not match any entry, forcing slapd to examine 
every entry in the DB, testing the filter for a match.

Essentially the slapd entry cache in back-bdb/back-hdb is so efficient the search 
processing time is almost invisible; the runtime is limited only by the memory 
bandwidth of the machine. (The search data rate corresponds to about 3.5GB/sec; 
the memory bandwidth on the machine is only about 4GB/sec due to ECC and register latency.)

H3: New overlays

* slapo-constraint (Attribute value constraints)
* slapo-dds (Dynamic Directory Services, RFC 2589)
* slapo-memberof (reverse group membership maintenance)

H3: New features in existing Overlays

* slapo-pcache
  - Inspection/Maintenance 
    -- the cache database can be directly accessed via
       LDAP by adding a specific control to each LDAP request; a specific
       extended operation allows to consistently remove cached entries and entire
       cached queries
  - Hot Restart
    -- cached queries are saved on disk at shutdown, and reloaded if
      not expired yet at subsequent restart

* slapo-rwm can safely interoperate with other overlays
* Dyngroup/Dynlist merge, plus security enhancements
  - added dgIdentity support (draft-haripriya-dynamicgroup)

H3: New features in slapd

* monitoring of back-{b,h}db: cache fill-in, non-indexed searches,
* session tracking control (draft-wahl-ldap-session)
* subtree delete in back-sql (draft-armijo-ldap-treedelete)
* sorted values in multivalued attributes for faster matching 
* lightweight dispatcher for greater throughput under heavy load and on
multiprocessor machines. (33% faster than 2.3 on AMD quad-socket dual-core server.)


H3: New features in libldap

* ldap_sync client API (LDAP Content Sync Operation, RFC 4533)

H3: New clients, tools and tool enhancements

* ldapexop for arbitrary extended operations
* Complete support of controls in request/response for all clients
* LDAP Client tools now honor SRV records 

H3: New build options

* Support for building against GnuTLS


H2: Obsolete Features Removed From 2.4

These features were strongly deprecated in 2.3 and removed in 2.4.

H3: Slurpd

Please read the {{SECT:Replication}} section as to why this is no longer in
OpenLDAP

H3: back-ldbm

back-ldbm was both slow and unreliable. Its byzantine indexing code was
prone to spontaneous corruption, as were the underlying database libraries
that were commonly used (e.g. GDBM or NDBM). back-bdb and back-hdb are
superior in every aspect, with simplified indexing to avoid index corruption,
fine-grained locking for greater concurrency, hierarchical caching for
greater performance, streamlined on-disk format for greater efficiency
and portability, and full transaction support for greater reliability.
