julien at trigofacile.com
Mon May 18 06:52:11 UTC 2009
> I think what your current fix will do is force the file to be remapped
> any time any article write has happened except for a write at the
> high-water mark and a search or article read that isn't at the
> high-water mark.
Yes, that's it.
If an overview data contains article numbers:
2 - 3 - 9 - 6 - 4
in that order. Then remapping is done when an article whose number
is < 9 is written. It should not happen in normal overview use
since the numbers are increasing.
Remapping is also done before the start of a search in case
the mapped file only contains:
2 - 3
and we are searching in the range 2-15. As we know that the high
water mark is 9, we remap in order to find 2,3,9,6,4.
If we were searching in the range 2-6, there would not have been
any problem (because the file would already have been remapped
after the arrival of #6, following #9).
> I think that the patch does more than is necessary. It should be fine
> if we fill in a hole in the overview below high
Yes it would be better. Though I do not see either tdx_data_store
or tdx_data_add searching for such a hole (we have to find one,
and of a sufficient length).
> The problem, and what I suspect the test
> is triggering, is when we've *rebased* the overview because we wrote
> below the overview base number rather than just anything below the
> high-water mark.
You're right; the overview data is "repacked" in this case.
> I suspect that if we just remapped when we rebased,
> that would also solve the problem.
> We still break the guarantee of OVSTATICSEARCH if there's an outstanding
> search, though. I wonder if we should really keep track of whether
> there's an open search and change behavior in that case.
Remapping is done only when an open search is wanted (and after it begins).
When there is a rebase, remapping will currently be done and also if
there is an outstanding search.
I do not see well what you prefer to do (except for filling overview holes
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