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https://issues.apache.org/jira/browse/HDDS-7743?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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George Jahad reassigned HDDS-7743:
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Assignee: (was: George Jahad)
> [Snapshot] Implement snapshot disk usage
> ----------------------------------------
>
> Key: HDDS-7743
> URL: https://issues.apache.org/jira/browse/HDDS-7743
> Project: Apache Ozone
> Issue Type: Sub-task
> Reporter: Siyao Meng
> Priority: Major
>
> (Excerpt from the design doc)
> We could show two sizes of a snapshot (terms borrowed from btrfs):
> a. Referenced size: total size of all the keys in the snapshot. This
> indicates how much space it would take on the target cluster when replicated.
> Basically this is du on the bucket inside the DB checkpoint. Use the existing
> counter (space used) implemented for quota.
> b. Exclusive size: the size of keys exclusively referenced by this snapshot.
> This indicates how much space (times replication factor) can be released from
> the cluster when the snapshot is deleted and garbage collected.
> (i) The exclusive size calculation can be done with the help of deletedTable
> in the next snapshot (or active filesystem’s if it is the last snapshot).
> Iterate over next snapshot’s deletedTable (and delayedDeletedTable), count
> the number of keys that exist in the current snapshot, and return the sum of
> those key sizes.
> (ii) The exclusive size of a snapshot can fluctuate (typically increase) when
> a neighboring snapshot is deleted because of the deletedTable merge. Still,
> for a read-only snapshot, we can calculate this in a background thread and
> persist the size. And whenever a neighboring snapshot is deleted, the
> persisted value is invalidated and would have to be calculated again
> (possibly incrementally).
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