[PATCH] GUID index for LDB

Stefan Metzmacher metze at samba.org
Wed Sep 6 23:25:39 UTC 2017

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 ?

> 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...

> We use a number of tricks to ensure we don't waste the expense of the
> casefold. 
>> Is it expected that only some workloads are faster?
> Yes.  It is delete from an index that hurts the most in the current
> code (linear scan), the rest of the benefit comes from having a smaller
> index overall, reducing the memcpy time in the read and transaction
> commit. 
>> Do these numbers already include the BINARY_SEARCH patches?
> Yes.
>>> This series also passes a full make test.  It also showed some flapping
>>> tests, so I plan to chase those down and I look forward to a positive
>>> review!
>> I guess you'll resort the commits so that the version bump happens
>> at the end just before the final patch that activates it in Samba?
> Yes, that is the plan.
>> Can you also run an autobuild without the activation in Samba,
>> so that we're sure we don't insert regressions for possible backports?
> Yes, I'll check it with and without activation. 
> I have another proposal for the changes that need to make it in for 4.7
> in a distinct thread.

I noticed that...


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