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https://issues.apache.org/jira/browse/HBASE-21070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16594402#comment-16594402
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Mingliang Liu commented on HBASE-21070:
---------------------------------------
The patch looks good to me overall to remove the dependency on last modified
time of top snapshort dir, which is not necessarily updated per [Hadoop
FileSystem
contract|https://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/filesystem/introduction.html#Timestamps].
The {{readLock}} is not used and can be removed. If all access to the {{cache}}
and {{snapshots}} are accessed via {{synchronized}}, we don't need the
{{volatile}} keyword here. {{triggerCacheRefreshForTesting()}} can be
{{synchronized}} I think.
> SnapshotFileCache won't update for snapshots stored in S3
> ---------------------------------------------------------
>
> Key: HBASE-21070
> URL: https://issues.apache.org/jira/browse/HBASE-21070
> Project: HBase
> Issue Type: Bug
> Components: snapshots
> Affects Versions: 3.0.0, 2.1.1, 1.4.7
> Reporter: Zach York
> Assignee: Zach York
> Priority: Critical
> Labels: FSRedo
> Attachments: HBASE-21070.master.001.patch,
> HBASE-21070.master.002.patch
>
>
> The SnapshotFileCache depends on last modified time to determine whether to
> update the Snapshot HFile cache. However, in S3, real 'folders' don't exist.
> S3 filesystems create a dummy file in place of a folder, but the dummy file
> last modified time is not updated when files are changed 'under' it. This
> means that the SnapshotFileCache doesn't pick up new snapshot HFiles and
> these files aren't removed from the HFileCleaner and can be eligible for
> deletion.
>
> My patch removes the lastmodified assumption.
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