[389-devel] 389-devel Digest, Vol 99, Issue 6

Wed Sep 11 17:41:39 UTC 2013

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> Today's Topics:
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>     1. Re: RFC: New Design: Fine Grained ID List Size (Rich Megginson)
>     2. Re: RFC: New Design: Fine Grained ID List Size (Ludwig Krispenz)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 10 Sep 2013 08:29:14 -0600
> From: Rich Megginson <rmeggins at redhat.com>
> To: Ludwig Krispenz <lkrispen at redhat.com>
> Cc: "389 Directory server developer discussion."
> 	<389-devel at lists.fedoraproject.org>
> Subject: Re: [389-devel] RFC: New Design: Fine Grained ID List Size
> Message-ID: <522F2CBA.1040205 at redhat.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> 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)
>
>>>
>>>>>
>>>>>
>>>>> --
>>>>> 389-devel mailing list
>>>>> 389-devel at lists.fedoraproject.org
>>>>> https://admin.fedoraproject.org/mailman/listinfo/389-devel
>>>>
>>>> --
>>>> 389-devel mailing list
>>>> 389-devel at lists.fedoraproject.org
>>>> https://admin.fedoraproject.org/mailman/listinfo/389-devel
>>>
>>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 10 Sep 2013 16:35:07 +0200
> From: Ludwig Krispenz <lkrispen at redhat.com>
> To: Rich Megginson <rmeggins at redhat.com>
> Cc: "389 Directory server developer discussion."
> 	<389-devel at lists.fedoraproject.org>
> Subject: Re: [389-devel] RFC: New Design: Fine Grained ID List Size
> Message-ID: <522F2E1B.9010600 at redhat.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
>
> On 09/10/2013 04:29 PM, Rich Megginson wrote:
>> 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.

Just out of curiosity, why is keeping a count per key a problem? If you're 
using BDB duplicate key support, can't you just use cursor->c_count() to get 
this? I.e., BDB already maintains key counts internally, why not leverage that?

-- 
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