[Lustre-devel] Doubly indexed tree / changelogs

[Peter Braam]

Sure, when aggregations apply.  But they do not apply in general (e.g.
Filesets that are search results) and we need a doubly indexed tree for
that.

Hence my question, what doubly indexed trees exist?

Peter


On 9/22/08 3:05 PM, "Alex Zhuravlev" <Alex.Zhuravlev at Sun.COM> wrote:

> IMHO, it'd be useful to insert aggregations into that index.
> just to keep the index small. say, subtree?
> 
> thanks, Alex
> 
> Peter Braam wrote:
>> Objects can be in many filesets, and be added to some, removed from others.
>> 
>> I think this is an almost arbitrary collection of pairs (FID, fileset-id)
>> and we need it indexed by both.
>> 
>> Peter
>> 
>> 
>> On 9/22/08 1:52 PM, "Alex Zhuravlev" <Alex.Zhuravlev at Sun.COM> wrote:
>> 
>>> can object migrate between filesets? if not, we probably
>>> can use fid's sequence as a record in that index?
>>> 
>>> thanks, Alex
>>> 
>>> Peter Braam wrote:
>>>> Hi Nikita, Nathan -
>>>> 
>>>> After some pondering I have come to two conclusions.
>>>> 
>>>> To encode filesets, we need a tree that makes two iterations fast:
>>>> 
>>>>    1. list all filesets that contain a certain object
>>>>    2. list all objects in a certain fileset
>>>> 
>>>> 
>>>> Is there a doubly indexed tree for this?
>>>> 
>>>> Secondly, to make the changelogs useful and scalable for filesets we
>>>> will need to be able to list all changelog entries associated with a
>>>> certain inode efficiently.  I see two ways to do this ­ one is an
>>>> auxiliary directory file mapping inodes to many changelog entries, the
>>>> second is to embed forward and backward pointers in the changelog
>>>> entries to build a linked list rooted at the inode (using an EA in the
>>>> inode pointing to the first and last element of the list).  Both have
>>>> some overheads.  What are your thoughts?
>>>> 
>>>> Peter
>>>> 
>>>> 
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>> 
>> 
>