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https://issues.apache.org/jira/browse/HADOOP-13449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15717170#comment-15717170
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Mingliang Liu commented on HADOOP-13449:
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Yes I did consider putting all the ancestors to the metadata store when putting
a single path. Another benefit is that, {{isEmpty}} will be much easier: simply
issue a query request (limit return size 1) whose hash key ("parent" field) is
the specific directory, and if there is any data returned, the directory is
non-empty; else empty. Then the case that {{/a, /a/b/c, /a/b/d}} yet {{/a}} is
not empty, does not exist. Plus we don't have to store/maintain the {{isEmpty}}
field any longer.
I gave up this constraints when implementing DDB and let the file system
enforces this for the sake of performance. Consider a simple case: to
{{put(PathMetadata meta)}} 1K files in a deep directory (say 10 layers), every
put operation will check if all the ancestors exist, and 1K operation becomes
10K operations to DDB. For {{put(DirListingMetadata meta)}}, it will be
efficient so we can blame users for not using this one instead.
So overall, not changing MetadataStore is possible and we can change this in
the {{DynamoDBMetadataStore}} implementation. I'll post a patch (may be a wip
one) soon.
So we did find real bugs/problems/limitation via integration tests; and they're
helpful. Thanks,
> S3Guard: Implement DynamoDBMetadataStore.
> -----------------------------------------
>
> Key: HADOOP-13449
> URL: https://issues.apache.org/jira/browse/HADOOP-13449
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Chris Nauroth
> Assignee: Mingliang Liu
> Attachments: HADOOP-13449-HADOOP-13345.000.patch,
> HADOOP-13449-HADOOP-13345.001.patch, HADOOP-13449-HADOOP-13345.002.patch,
> HADOOP-13449-HADOOP-13345.003.patch, HADOOP-13449-HADOOP-13345.004.patch,
> HADOOP-13449-HADOOP-13345.005.patch, HADOOP-13449-HADOOP-13345.006.patch,
> HADOOP-13449-HADOOP-13345.007.patch, HADOOP-13449-HADOOP-13345.008.patch,
> HADOOP-13449-HADOOP-13345.009.patch, HADOOP-13449-HADOOP-13345.010.patch
>
>
> Provide an implementation of the metadata store backed by DynamoDB.
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