bcachefs
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Towards snapshots
🕑 Added 2019-12-29 17:36:19 +0000 UTCJust finished a major rework that gets us a step closer to snapshots: the btree code is incrementally being changed to handle extents like regular keys.
Previously, when reading in a btree node we'd have to check for and handle partially overwritten extents, as part of the mergesort we do (btree nodes are log structured). But the plan for snapshots will break this algorithm; storing extents from different snapshots in the same position in the btree breaks the ordering requirements for this algorithm.
Now, the extent update path emits whiteouts and new extents when partially overwriting existing extents as needed, so that the btree node read path (and a fair amount of other code) can use the same algorithm we use for btree nodes that store regular keys. So besides being necessary for snapshots, this is also a nice cleanup and simplification of the existing code.
Next up - the handling of overwriting existing extents has to be lifted up further, to above where journalling happens; journal replay also has to do a sort that handles overwrites, and it is also going to need to be able to treat extents like regular keys for snapshots.
Comments
More bugs found just means more users!
Kent Overstreet
I've been embarrassed by the number of bugs we've been finding lately :/ I'll try to get one up soon though.
Hi, any status update? Half a year has passed since the last one...
brunoais
Awesome to know that! Keep up the great work!
