On Tue, Jun 30, 2009 at 09:08:17AM -0700, Jeremy Archer wrote:
> Hi Darren,
>
> Thanks for replying.
>
> I am confused then. What is the purpose of incorporating the birth txg
> in the arc hash?
Consider:
TXG action
5 write of first block of File A, assigned DVA 5, birth TXG 5
10 file A is deleted
15 write to first block of File B, assigned DVA 5 birth TXG 15
The two blocks are distinct, and are cached seperately in the ARC.
Cheers,
- jonathan
> How do 2 different files find a shared block?
>
> Obviously, the first one has to read it from disk, and subsequently remember
> the
> birth txg in addition to to the dva.
>
> How does the 2nd file know what is the birth txg of the desired block?
> Does each file have do an initial read from disk to learn the birth txg of
> the block?
>
> I am looking for easy to understand metaphores,
> such as "cache entries are valid for current txg only"...
> but it looks I am out of luck in this case.
> --
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