On 7.6.2013 16:11, Rich Megginson wrote:
On 06/07/2013 05:42 AM, Petr Spacek wrote:
> I would like to get opinions from 389 gurus to following problem.
>
> I have an application (DNS server), which needs to read content of whole one
> sub-tree (cn=dns, dc=test) and keep it synchronized.
>
> The work flow is:
> 1) Application (DNS server) starts
> 2) Application reads all existing data out from the sub-tree
> 3) Application does /something/ with the existing data and starts replying
> to application clients
> 4) Sub-tree has to be kept in sync with LDAP server, i.e. updates from LDAP
> server should be incrementally applied to the 'state' inside the application
>
>
> The problem with persistent search is that it doesn't offer any reliable
> 'signal' that step (2) ended. The search is just running for infinite time
> and I can't find any signal that all existing entries were read already and
> now the application will get only Entry Change Notifications.
>
>
> Basically, I'm looking for something like LDAP syncRepl in refreshAndPersist
> mode with no cookie (RFC 4533 section 1.3.2 and section 3.4).
>
>
> I know that Entry Change Notification from persistent search contains bit
> field which denotes if the entry was added/modified/deleted/nothing (i.e.
> not modified, just read). Unfortunately, this bit field can't be used for
> *reliable* detection that all existing entries were read.
>
>
> Could this 'hack' work reliably?
> 1) Start persistent search (in separate application thread), but suspend
> result processing.
> 2) In another application thread, do the normal sub-tree search on the same
> sub-tree. Normal search will be started *after* the persistent search.
> 3) Process all results from normal search first
> 4) Do /something application specific/
> 5) Start processing updates from persistent search
>
> In my application I can cope with duplicates, when 'normal' search returned
> entry cn=xyz and the persistent search returned the same entry cn=xyz again.
Could you use entryUSN? For example - keep searching until the entryUSN in
the entry is the same as the global entryUSN, then fallback to persistent search?
Could you elaborate it a bit more, please? I'm not sure if I understood.
What exactly 'global' entryUSN means?
Do you mean 'lastUSN' value on particular server?
Can it work on server where modification are scarce? (Note that I do sub-tree
search on subset of the whole database.)
I considered normal search followed by persistent search with entryUSN filter,
but IMHO it will not work with entry deletion.
For example:
1) Start normal search and request entryUSN attribute (among others)
2) Process all results from search and compute max(entryUSN)
3) Start persistent search with filter (entryUSN > computedMaxValue)
I can see the race condition if an entry is deleted between steps (2) and (3).
That is exactly what I tried to solve with 'parallel' searches, i.e.
effectively avoid any time gap between steps (2) and (3).
Of course, I could read entryUSN during normal and persistent search and then
skip all results from persistent search with entryUSN < computedMaxValue. Is
that what you meant?
> I can see another option:
> To implement 389 plugin which will provide (very partial) support for RFC
> 4533. The idea is to implement only state-less pieces (no cookies) and
> return some error when client attempts to use a cookie.
This would also likely use entryUSN for the cookie, internallly.
Yes, that was also
my idea, but I don't want to implement the 'state-full
part' of the RFC in all it's complexity. Now I'm interested only in detection
that all existing entries were read :-)
> Could somebody judge how difficult it can be? From my (naive)
point of view
> are state-less parts of RFC 4533 only 'persistent search encapsulated in
> another LDAP controls'.
Thank you very much for your time.
--
Petr^2 Spacek