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https://issues.apache.org/jira/browse/HADOOP-13449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15668965#comment-15668965
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Aaron Fabbri commented on HADOOP-13449:
---------------------------------------
{quote}
But for listStatus(), my understanding is that we assume the entry per se is
there.
{quote}
The only thing that matters is the semantics or API contract. As long as you
have the behavior I outlined, it is correct.
We cannot require client to put(parent) before put(child), since we may run on
an existing bucket where the directory was already created before we started
our cluster.
{quote}Or else, if we query the DDB and no entries having parent as this path,
is the directory nonexistent, or the directory is empty? DDBMetadataStore
should return DirListingMetadata accordingly. Thanks,
{quote}
Ok, I think this is an implementation detail for DynamoDB. Two ideas. #1
seems pretty good:
1. Do a prefix scan.. I thought DynamoDB had built-in support for looking up
values by key prefix. I.e. {{begins_with}}. When you do a
listChildren(parent), you can just query for {{key begins_with parent}}?
2. Create the parent path when you create the child so you can implement
listChildren() properly (what I did for initial LocalMetadataStore).
Also, can't you use prefix queries to eliminate the whole
{{DescendantsIterator}} thing for recursive delete?
Thanks for the discussion [~liuml07].
> 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
>
>
> Provide an implementation of the metadata store backed by DynamoDB.
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