On  7.03.2018 14:14, Qu Wenruo wrote:

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SHARED flag is determined after extent map merge, so here we can't rely
on em here.

Shouldn't extent maps correspond to 1:1 disk-state. I.e. they are just
the memory cache of the extent state. So if we merge them, shouldn't we
also merge the on-disk extents as well ?

Not 1:1.

In memory one is merged maybe to save memory.

But on-disk file extents has size limit.
For compressed one it's 128K and 128M for uncompressed one.

Fair enough, however 4 extents, 16k each should warrant merging on-disk
as well, no ?

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