Norval Hope wrote:
...
1. I'd be much happier if the ".schema file => schema partition"
tool were instead (or also) available as an optional start-up
mechanism activatable by uncommenting support in server.xml. In the
use-cases dear to my heart users are able to easily register dynamic
custom partitions along with the .schema files they depend on by
simply placing files in various filesystem directories (ala
appservers) rather then having to run separate utilities.
The utility can also generate an LDIF from .schema files (to add schema
changes) that can be applied once on startup which effectively gives you
what you want right?
Given this
point I'd most probably do away with a maven plugin for the ".schema
=> schema partition" bit and replace it with code to determine whether
the .schema partition needed to be populated with bootstrap
information on its first run after deployment (from .schema files
included in a release .jar). For dynamic updates/additions of .schema
files the relevant filesystem directories could be polled for changes
periodically (again ala appservers).
Yeah there is a problem here with having 2 copies of the same data.
Which one is the authoritative copy? We'll have the same data in a
.schema file on disk and in the DIT. Where do we make changes when the
schema is altered via the DIT? What do we do if the schema files are
changed on disk? What if there are conflicts? How will they be resolved?
2. Being able to change schema information is a very power-user
feature, but I'd imagine that a much more common usage is simply
wanting to add extra read-only schema information (matching various
RFCs and/or basically static schemas defined by third party vendors)
after deployment. In my usecases storing the thirdparty (i.e.
non-core) schema information persistently is actually a minus rather
then a plus; I'd prefer my users could deploy another custom partition
Another partition?
with updated schema information and restart AD without having to worry
about clashes with existing information. Is it theoretically possible
to indentify various schema subtrees as "read-only" so that they can't
be changed and aren't persisted, but are instead transiently populated
from .schema files at start-up?
Might be able to do this but I'm very against the idea of parsing
.schema files on startup. Plus there are things you cannot store in
.schema files that you can store in the DIT. Like normalizers,
syntaxCheckers and comparators.
3. Whether modifying schema information via piece-meal updates or
whole .schema file imports, we face questions re versioning / draining
of pending requests referring to old version of the schema etc. Is the
race condition between schema changes and other operations referring
to the schema some that needs to be considered now, say by
synchronizing access to the schema partition.
Schema information under this new design is just like any kind of data
within the server. The same shared/exclusive lock requirements apply
wrt read/write opertions.
I know my focus is out of whack with AD's primary objectives, in that
I don't use it as a persistent store at all,
NP.
but even so I see
populating at start-up rather then maven plugin + import utility
Note that this maven plugin is not for general use. It is used to
pre-build the schema partition that will be deposited on disk if the
schema partition has not yet been created.
As for the import utility it can just generate an LDIF of that you can
load on startup. You can provide schemas in LDIF format for your users.
The good thing with AD is that if you load an LDIF on startup AD marks
that LDIF file as already having been loaded and will not load it again.
It keeps a record of what was loaded when under the ou=system area.
as a
universal plus in terms of flexibility / amount of code required.
I think some points I did not make clear. The schema partition is a
single partition that will always be present just like the system
partition. You will not be loading schema info into just any partition.
This partition is dedicated and fixed at ou=system. Regardless of the
VD you're building you'll still need to have this schema partition or
ApacheDS or your derived virtual directory will not start.
What are some of your requirements for the VD you're working on?
Alex
