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From Emmanuel Lecharny <elecha...@gmail.com>
Subject Re: Paged Search Control questions
Date Sun, 14 Dec 2008 17:26:36 GMT
Howard Chu wrote:
> Emmanuel Lecharny wrote:
>> Stefan Seelmann wrote:
>>> Emmanuel Lecharny wrote:
>>>
>>>> Another one :
>>>>
>>>> suppose we have a normal user doing a search request with a 
>>>> sizeLimit of
>>>> 10, with the server limit set to 5, and the potential result would 
>>>> be 7
>>>> entries (so the result will be truncated to 5 entries due to the 
>>>> server
>>>> limit) :
>>>> - should we generate a SizeLimitExceededException ?
>>>>
>>> Do we generate such an SizeLimitExceededException when doing a normal
>>> search request without the paged search control? I guess yes. So I 
>>> think
>>> we should also return an LDAP code 4 here.
>>>
>> Seems like Openldap behaves this way. So ADS will generate a code 4 if
>> the server size limit is exceeded.
>>
>> Thanks Stefan !
>
> Sorry for jumping in here late, wanted to reply earlier but on dialup 
> right now so it's not always convenient... Still, it looks like Stefan 
> covered all the bases already.
Yep, and you confirmed that he was plain right :) Sometime, when you try 
to implement something, you'd better ask those who 'know' :)
>
> To summarize: using the Paging control should only be considered a 
> form of XON/XOFF flow control for a single Search request. It cannot 
> (MUST not) change the server's behavior wrt the overall size limits in 
> effect. 
This was a part of the spec I mis-understood, clearly. It makes a hell 
of sense to consider that the sizeLimit is global, ad should be 
considered across the multiple paged searches. The funny part is that I 
have injected such a counter in the internal structure before asking the 
question, I don't know what for, and now, I see the reason. The 
reptilian part of my brain knew it ;)
> MS AD is broken in this respect (which is particularly pathetic given 
> that some MS folks co-authored the spec, but so it goes).
> I.e., when no control is present, the search result set will be the 
> smaller of the client's requested size limit, and any administrative 
> limits configured on the server. With the control present, the total 
> number of returned entries allowed is still the same, just that they 
> may be received by the client in smaller groups.
On don't see where is the problem here ... Suppose you have a server 
size limit (SL), a request size limit (RL) and a paged size limit (PL), 
the expected behavior when not using the control should be :

- return min( SL, RL) entries

and if the control is present :

if ( PL < min ( SL, RL ) )
  while ( count < min( SL, RL ) ) do
    return PL entries or less
    count += number of returned entries
  done
else
  return min( SL, RL )

so in the second case, the client will receive entries in PL sized 
groups, until we reach the server limit or the request limit ?
>
> Also beware of another issue: the spec says the page size is an 
> Integer but MS AD implements it as an unsigned, and there are MS 
> clients out there that expect to be able to set the max size (god 
> knows why, since that effectively disables paging) 
MS client, you mean the utterly crap named LDP ? Ok, we have to take 
care of that, and consider that a negative number means something like 
the max number of entries then. Easy. Thanks for the warning :)
> and will implode when they receive a ProtocolError in response to such 
> an erroneous request. (I've forgotten the ID# of the bug report in our 
> tracker...) All in all it's a crummy spec and you can pretty much bet 
> that when you run across a client that depends on it, the client is 
> broken in a lot of other ways.
That's the funniest part of the job : deal with other's errors when you 
already have enough of your own in your plate !

Thanks Howard !


-- 
--
cordialement, regards,
Emmanuel L├ęcharny
www.iktek.com
directory.apache.org



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