[PATCH] GUID index for LDB

[Stefan Metzmacher]

Am 07.09.2017 um 01:46 schrieb Andrew Bartlett:
> On Thu, 2017-09-07 at 01:25 +0200, Stefan Metzmacher wrote:
>> Hi Andrew,
>>
>>>> So there's no performance loss of 5% for searches?
>>>
>>> There might be, but I don't think so.  Our experience is that even
>>> after several runs the numbers below 5% are not statistically
>>> significant, as the absolute values have too much noise.  Watch how
>>> the
>>> 'do nothing' line moves around for an idea.  I'll mail you the full
>>> results file and the absolute values graph tomorrow. 
>>>
>>>> As we're now doing one more hop from the index (now via the
>>>> objectGUID)
>>>> to the dn.
>>>
>>> We only change the cost for a base DN search really, plus the cost
>>> of
>>> checking the base for a subtree search.  
>>>
>>> Anything in an index avoids going from a DN -> key with a casefold,
>>> as
>>> both the contents of the index and the key in the DB now match
>>> exactly
>>> (plus a prefix). 
>>>
>>> So an indexed search that was:
>>>  - index -> casefold -> key
>>> is:
>>>  - index -> key
>>
>> Isn't it index -> GUID-key -> DN->key ?
> 
> No (unless you count the memcpy() for the GUID=prefix as the GUID-key
> step).
> 
>>> and a base search that was:
>>>  - DN -> casefold -> key
>>> is:
>>>  - DN -> index -> key
>>
>> I don't understand that case...
>>
>> Do you actually change the primary key for the records to be GUID
>> based?
>> I thought you would only change the index and keep the real objects
>> as they're now...
> 
> Correct, I move all the objects to allow (as should have been
> originally designed) the values in the index to be trivially converted
> into TDB keys. 

And how does the upgrade/downgrade works then?

>>
>> I noticed that...
> 
> I've fixed a couple of issues and am tidying that up today.  I've
> verified it allows a downgrade of a backend TDB by editing @INDEXLIST,
> which could then be followed by a dbcheck --reindex.  
> 
> This is helpful if folks downgrade from 4.8 to 4.7 and forget the run
> the (to be written) downgrade script first. 

Can you explain the upgrade/downgrade and the overall design changes
in explicit/verbose text form?

Thanks!
metze


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