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From "Mingliang Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13449) S3Guard: Implement DynamoDBMetadataStore.
Date Sat, 03 Dec 2016 02:11:58 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15717170#comment-15717170

Mingliang Liu commented on HADOOP-13449:

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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