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From "Aaron Fabbri (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HADOOP-15489) S3Guard to self update on directory listings of S3
Date Fri, 25 May 2018 06:09:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16490281#comment-16490281
] 

Aaron Fabbri edited comment on HADOOP-15489 at 5/25/18 6:08 AM:
----------------------------------------------------------------

Look at S3Guard#dirListingUnion().  We used to always update MetadataStore at the end of listStatus().
Later we changed it to only happen when fs.s3a.metadatastore.authoritative = true.

If you set this to true you will always update MetadataStore at end of listStatus(), but keep
in mind that the short-circuit listings are not implemented for Dynamo MS yet ([~gabor.bota]
is working towards that though). So, you would get the behavior you want for getFileStatus()
(short-circuit / skip S3) but not listStatus() etc.

There are the other listing APIs that don't update the MetadataStore, though.


was (Author: fabbri):
Look at S3Guard#dirListingUnion().  We used to always update MetadataStore at the end of listStatus().
Later we changed it to only happen when fs.s3a.metadatastore.authoritative = true.

If you set this to true you will always update MetadataStore at end of listStatus(), but keep
in mind that the short-circuit listings are not implemented for Dynamo MS yet ([~gabor.bota]
is working towards that though).

There are other listing APIs that don't do this, of course.

> S3Guard to self update on directory listings of S3
> --------------------------------------------------
>
>                 Key: HADOOP-15489
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15489
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 3.1.0
>         Environment: s3guard
>            Reporter: Steve Loughran
>            Priority: Major
>
> S3Guard updates its table on a getFileStatus call, but not on a directory listing.
> While this makes directory listings faster (no need to push out an update), it slows
down subsequent queries of the files, such as a sequence of:
> {code}
> statuses = s3a.listFiles(dir)
> for (status: statuses) {
>   if (status.isFile) {
>       try(is = s3a.open(status.getPath())) {
>         ... do something
>       }
> }
> {code}
> this is because the open() is doing the getFileStatus check, even after the listing.
> Updating the DDB tables after a listing would give those reads a speedup, albeit at the
expense of initiating a (bulk) update in the list call. Of course, we could consider making
that async, though that design (essentially a write-buffer) would require the buffer to be
checked in the reads too. 



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