HAMMER filesystem update - design document

Chris Turner c.turner at 199technologies.org
Fri Oct 12 15:17:12 PDT 2007

Matthew Dillon wrote:
>     It will be cluster-by-cluster to begin with.  I don't expect it to cause
>     any issues, the BxTree in each cluster will be fairly compact and well
>     cached and, most importantly, nearly all write I/O can be asynchronous
>     so locks simply will not be held all that long.
>     Eventually it will be possible to use inherent buffer cache locks to
>     lock the BxTree operations but its a little dicey to try to do
>     that level of fine-grained locking by default due to the allocation
>     model.

Anyone up on ReiserFS ?

(but still capable of a 'clean room' description :)

As I recall, according to their docs it seems to have been one of the
first to use BTrees in the general sense for internal structuring ..

also as I recall, there were some performance problems in specific areas
of requiring extra CPU for basic IO (due to having to compute tree
operations rather than do simple pointer manipulations) and also
concurrent IO (due to the need for complex tree locking types of things,
possibly compounded by the extra cpu time)

this kind of a thing is more for replication than 100% raw speed, but
in any case.. just some topics for discussion I suppose ..

I still need to read the more detailed commits.

looking forward to it.

- Chris

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