[389-devel] RFC: New Design: Fine Grained ID List Size

[Ludwig Krispenz]

On 09/09/2013 07:19 PM, Rich Megginson wrote:
> On 09/09/2013 02:27 AM, Ludwig Krispenz wrote:
>>
>> On 09/07/2013 05:02 AM, David Boreham wrote:
>>> On 9/6/2013 8:49 PM, Nathan Kinder wrote:
>>>> This is a good idea, and it is something that we discussed briefly 
>>>> off-list.  The only downside is that we need to change the index 
>>>> format to keep a count of ids for each key.  Implementing this 
>>>> isn't a big problem, but it does mean that the existing indexes 
>>>> need to be updated to populate the count based off of the contents 
>>>> (as you mention above).
>>>
>>> I don't think you need to do this (I certainly wasn't advocating 
>>> doing so). The "statistics" state is much the same as that proposed 
>>> in Rich's design. In fact you could probably just use that same 
>>> information. My idea is more about where and how you use the 
>>> information. All you need is something associated with each index 
>>> that says "not much point looking here if you're after something 
>>> specific, move along, look somewhere else instead". This is much the 
>>> same information as "don't use a high scan limit here".
>>>
>>>>
>>>> In the short term, we are looking for a way to be able to improve 
>>>> performance for specific search filters that are not possible to 
>>>> modify on the client side (for whatever reason) while leaving the 
>>>> index file format exactly as it is.  I still feel that there is 
>>>> potentially great value in keeping a count of ids per key so we can 
>>>> optimize things on the server side automatically without the need 
>>>> for complex index configuration on the administrator's part. I 
>>>> think we should consider this for an additional future enhancement.
>>>
>>> I'm saying the same thing. Keeping a cardinality count per key is 
>>> way more than I'm proposing, and I'm not sure how useful that would 
>>> be anyway, unless you want to do OLAP in the DS ;)
>> we have the cardinality of the key in old-idl and this makes some 
>> searches where parts of the filter are allids fast.
>>
>> I'm late in the discussion, but I think Rich's proposal is very 
>> promising to address all the problems related to allids in new-idl.
>>
>> We could then eventually rework filter ordering based on these 
>> configurations. Right now we only have a filter ordering based on 
>> index type and try to postpone "<=" or similar filter as they are 
>> known to be costly, but this could be more elaborate.
>>
>> An alternative would be to have some kind of index lookup caching. In 
>> the example in ticket 47474 the filter is 
>> (&(|(objectClass=organizationalPerson)(objectClass=inetOrgPerson)(objectClass=organization)(objectClass=organizationalUnit)(objectClass=groupOf
>> Names)(objectClass=groupOfUniqueNames)(objectClass=group))(c3sUserID=EndUser0000078458))" 
>> and probably only the "c3sUserID=xxxxx" part will change, if we cache 
>> the result for the (&(|(objectClass=... part, even if it is 
>> expensive, it would be done only once.
>
> Thanks everyone for the comments.  I have added Noriko's suggestion:
> http://port389.org/wiki/Design/Fine_Grained_ID_List_Size
>
> David, Ludwig: Does the current design address your concerns, and/or 
> provide the necessary first step for further refinements?
yes, the topic of filter reordering or caching could be looked at 
independently.

Just one concern abou the syntax:

nsIndexIDListScanLimit: maxsize[:indextype][:flag[,flag...]][:value[,value...]]

since everything is optional, how do you decide if in 
nsIndexIDListScanLimit: 6:eq:AND "AND" is a value or a flag ?
and as it defines limits for specific keys, could the attributname 
reflect this, eg nsIndexKeyIDListScanLimit or nsIndexKeyScanLimit or ... ?
>
>>>
>>>
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>>
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