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https://issues.apache.org/jira/browse/HDFS-11926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16040147#comment-16040147
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Weiwei Yang commented on HDFS-11926:
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This is the doc from RocksDB, could levelDB be same?
bq. A Snapshot API allows an application to create a point-in-time view of a
database. The Get and Iterator APIs can be used to read data from a specified
snapshot. In a sense, a Snapshot and an Iterator both provide a point-in-time
view of the database, but their implementations are different. Short lived
scans are best done via an iterator while long-running scans are better done
via a snapshot. An iterator keeps a reference count on all underlying files
that correspond to that point-in-time-view of the database - these files are
not deleted until the Iterator is released. A snapshot, on the other hand, does
not prevent file deletions; instead the compaction process understands the
existence of snapshots and promises never to delete a key that is visible in
any existing snapshot.
If levelDB is the same, then iterator should be enough for getRangKVs function,
as this should be a short lived scan, actually more consistent (prevent file
deletions).
> Ozone: Implement a common helper to return a range of KVs in levelDB
> --------------------------------------------------------------------
>
> Key: HDFS-11926
> URL: https://issues.apache.org/jira/browse/HDFS-11926
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ozone
> Reporter: Weiwei Yang
> Assignee: Weiwei Yang
> Priority: Blocker
> Attachments: HDFS-11926-HDFS-7240.001.patch,
> HDFS-11926-HDFS-7240.002.patch, HDFS-11926-HDFS-7240.003.patch,
> HDFS-11926-HDFS-7240.004.patch
>
>
> There are quite some *LIST* operations need to get a range of keys or values
> from levelDB, and filter entries with key prefix.
> # HDFS-11782 listKeys
> # HDFS-11779 listBuckets
> # HDFS-11773 listVolumes
> # HDFS-11679 listContainers
> we need to implement a common utility for them.
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