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https://issues.apache.org/jira/browse/HADOOP-15400?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Gabor Bota updated HADOOP-15400:
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Attachment: HADOOP-15400.001.patch
> Improve S3Guard documentation on Authoritative Mode implementation
> ------------------------------------------------------------------
>
> Key: HADOOP-15400
> URL: https://issues.apache.org/jira/browse/HADOOP-15400
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.0.1
> Reporter: Aaron Fabbri
> Assignee: Gabor Bota
> Priority: Minor
> Attachments: HADOOP-15400.001.patch
>
>
> Part of the design of S3Guard is support for skipping the call to S3
> listObjects and serving directory listings out of the MetadataStore under
> certain circumstances. This feature is called "authoritative" mode. I've
> talked to many people about this feature and it seems to be universally
> confusing.
> I suggest we improve / add a section to the s3guard.md site docs elaborating
> on what Authoritative Mode is.
> It is *not* treating the MetadataStore (e.g. dynamodb) as the source of truth
> in general.
> It *is* the ability to short-circuit S3 list objects and serve listings from
> the MetadataStore in some circumstances:
> For S3A to skip S3's list objects on some *path*, and serve it directly from
> the MetadataStore, the following things must all be true:
> # The MetadataStore implementation persists the bit
> {{DirListingMetadata.isAuthorititative}} set when calling
> {{MetadataStore#put(DirListingMetadata)}}
> # The S3A client is configured to allow metadatastore to be authoritative
> source of a directory listing (fs.s3a.metadatastore.authoritative=true).
> # The MetadataStore has a full listing for *path* stored in it. This only
> happens if the FS client (s3a) explicitly has stored a full directory listing
> with {{DirListingMetadata.isAuthorititative=true}} before the said listing
> request happens.
> Note that #1 only currently happens in LocalMetadataStore. Adding support to
> DynamoDBMetadataStore is covered in HADOOP-14154.
> Also, the multiple uses of the word "authoritative" are confusing. Two
> meanings are used:
> 1. In the FS client configuration fs.s3a.metadatastore.authoritative
> - Behavior of S3A code (not MetadataStore)
> - "S3A is allowed to skip S3.list() when it has full listing from
> MetadataStore"
> 2. MetadataStore
> When storing a dir listing, can set a bit isAuthoritative
> 1 : "full contents of directory"
> 0 : "may not be full listing"
> Note that a MetadataStore *MAY* persist this bit. (not *MUST*).
> We should probably rename the {{DirListingMetadata.isAuthorititative}} to
> {{.fullListing}} or at least put a comment where it is used to clarify its
> meaning.
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