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

[Rich Megginson]

On 09/10/2013 01:47 AM, Ludwig Krispenz wrote:
>
> 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 
> ... ?

Thanks, yes, it is ambiguous.
I think it may have to use keyword=value, so something like this:

nsIndexIDListScanLimit: limit=NNN [type=eq[,sub]] [flags=ADD[,OR]] 
[values=val[,val...]]

That should be easy to parse for both humans and machines.
For values, will have to figure out a way to have escapes (e.g. if a 
value contains a comma or an escape character).   Was thinking of using 
LDAP escapes (e.g. \, or \032)

>>
>>>>
>>>>
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>>>
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>>
>