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https://issues.apache.org/jira/browse/HADOOP-16279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16835785#comment-16835785
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Aaron Fabbri commented on HADOOP-16279:
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[~ste...@apache.org] I'd argue LocalMetadataStore is useful still-- but if I'm
the only one we could consider cutting it. You should be able to use it as a
metadata cache for read-only or single-writer operations to speed things up in
real world worlkloads (think setting it up as authoritative on a distcp, for
example).
I'll take a peek at the PR here. Thanks for working on this [~gabor.bota]
> S3Guard: Implement time-based (TTL) expiry for entries (and tombstones)
> -----------------------------------------------------------------------
>
> Key: HADOOP-16279
> URL: https://issues.apache.org/jira/browse/HADOOP-16279
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Gabor Bota
> Assignee: Gabor Bota
> Priority: Major
>
> In HADOOP-15621 we implemented TTL for Authoritative Directory Listings and
> added {{ExpirableMetadata}}. {{DDBPathMetadata}} extends {{PathMetadata}}
> extends {{ExpirableMetadata}}, so all metadata entries in ddb can expire, but
> the implementation is not done yet.
> To complete this feature the following should be done:
> * Add new tests for metadata entry and tombstone expiry to {{ITestS3GuardTtl}}
> * Implement metadata entry and tombstone expiry
> I would like to start a debate on whether we need to use separate expiry
> times for entries and tombstones. My +1 on not using separate settings - so
> only one config name and value.
> ----
> Notes:
> * In HADOOP-13649 the metadata TTL is implemented in LocalMetadataStore,
> using an existing feature in guava's cache implementation. Expiry is set with
> {{fs.s3a.s3guard.local.ttl}}.
> * LocalMetadataStore's TTL and this TTL is different. That TTL is using the
> guava cache's internal solution for the TTL of these entries. This is an
> S3AFileSystem level solution in S3Guard, a layer above all metadata store.
> * This is not the same, and not using the [DDB's TTL
> feature|https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/TTL.html].
> We need a different behavior than what ddb promises: [cleaning once a day
> with a background
> job|https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/howitworks-ttl.html]
> is not usable for this feature - although it can be used as a general
> cleanup solution separately and independently from S3Guard.
> * Use the same ttl for entries and authoritative directory listing
> * All entries can be expired. Then the returned metadata from the MS will be
> null.
> * Add two new methods pruneExpiredTtl() and pruneExpiredTtl(String keyPrefix)
> to MetadataStore interface. These methods will delete all expired metadata
> from the ms.
> * Use last_updated field in ms for both file metadata and authoritative
> directory expiry.
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