Re: (ITS#3939) min/max function extension to LDAP protocol

[quanah@stanford.edu]

--On Friday, August 19, 2005 11:41 PM -0700 "Kurt D. Zeilenga" 
<Kurt@OpenLDAP.org> wrote:

> At 11:22 PM 8/19/2005, Quanah Gibson-Mount wrote:
>
>
>> --On Friday, August 19, 2005 11:11 PM -0700 "Kurt D. Zeilenga"
>> <Kurt@OpenLDAP.org> wrote:
>>
>>> Well, what I noted was that there was an existing protocol
>>> mechanism to request return the entry with the lowest/highest
>>> CSN.
>>>
>>> I pretty much ignored most of rest of your post as it didn't
>>> make much sense to me at the time (and still doesn't).
>>
>> Okay, maybe this will explain it more:
>>
>> When the consumer connects to the provider, it tries to determine if it
>> needs to synch any data or not.
>
> It seems here you that you intend 'it' to refer to the consumer.
> That's incorrect.  When using LDAP sync, it is the provider
> which determines what data needs to be sent to sync the consumer.
> The provider does so by providing the cookie.


No, it is the provider.  The provider is trying to determine if the cookie 
sent to it is still valid or if changes need to be sent to the consumer. 
When the consumer's cookie is different than the providers, it does an 
internal search to determine if that cookie is still valid for its 
database.  This is extremely expensive.


For example, if the provider has a cookie of:

20050818185717Z#000001#00#000000

and the consumer has a cookie of:

20050818185716Z#000001#00#000000

The provider is going to run the following search:

entrycsn <= 20050818185716Z#000001#00#000000

to determine if there is one or more entries with a matching CSN.  If there 
isn't, the provider refreshes the consumer with all data.  If there is, it 
then only does an update of changes from the time the consumer last 
received data.

The problem is the <= search done by the provider.  That needs to be 
avoided.  If it was simply able to look at the lowest value CSN in its 
database, it would immediately be able to tell whether or not the consumer 
needs only a partial update, or a full update, and skip the entire <= 
search that can generate an enormous number of results altogether.

--Quanah


--
Quanah Gibson-Mount
Principal Software Developer
ITSS/Shared Services
Stanford University
GnuPG Public Key: http://www.stanford.edu/~quanah/pgp.html

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