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https://issues.apache.org/jira/browse/HADOOP-13936?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15852359#comment-15852359
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Aaron Fabbri commented on HADOOP-13936:
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I chatted with [~mackrorysd] a little bit about an additional modification time
column that records the age of each dynamodb entry. It was in the context of
the Prune CLI command he is working on. For pruning old metadata (files that
are presumably consistent in S3 now), the existing modification time seems to
be sufficient, as it reflects the likelihood of each file still being
inconsistent in S3.
For expiring cache entries, however, a separate "ddb entry modification time"
field seems useful.. In the context of this JIRA, where we want the
MetadataStore to "self heal" by timing out stale entries, we actually want a
timestamp for when the entry was last modified in DDB. The example that comes
to mind is when fs.s3a.metadatastore.authoritative is true (we allow caching
directory listings): we may load a directory listing with some old files
(created a year ago).. We want to time out those entries based on when they
were last written to DDB, not based on when the underlying S3 objects were
created.
> S3Guard: DynamoDB can go out of sync with S3AFileSystem::delete operation
> -------------------------------------------------------------------------
>
> Key: HADOOP-13936
> URL: https://issues.apache.org/jira/browse/HADOOP-13936
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Rajesh Balamohan
> Priority: Minor
>
> As a part of {{S3AFileSystem.delete}} operation {{innerDelete}} is invoked,
> which deletes keys from S3 in batches (default is 1000). But DynamoDB is
> updated only at the end of this operation. This can cause issues when
> deleting large number of keys.
> E.g, it is possible to get exception after deleting 1000 keys and in such
> cases dynamoDB would not be updated. This can cause DynamoDB to go out of
> sync.
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