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Date: Mon, 9 Nov 2015 22:12:11 +0000 (UTC)
From: "Zhe Zhang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.12864035.1442265655000.20935.1447107131271@Atlassian.JIRA>
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Subject: [jira] [Updated] (HDFS-9079) Erasure coding: preallocate multiple
 generation stamps and serialize updates from data streamers
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     [ https://issues.apache.org/jira/browse/HDFS-9079?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Zhe Zhang updated HDFS-9079:
----------------------------
    Attachment: HDFS-9079.09.patch

Fixed test failures from last Jenkins run, by addressing the following corner cases:
# In some test cases a streamer doesn't have any byte to write. Should properly handle the status of such streamers in the coordinator
# {{setExternalError}} should wait until the streamer is in {{DATA_STREAMING}} stage (i.e. {{blockStream}} is not null)

> Erasure coding: preallocate multiple generation stamps and serialize updates from data streamers
> ------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-9079
>                 URL: https://issues.apache.org/jira/browse/HDFS-9079
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: erasure-coding
>    Affects Versions: HDFS-7285
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-9079-HDFS-7285.00.patch, HDFS-9079.01.patch, HDFS-9079.02.patch, HDFS-9079.03.patch, HDFS-9079.04.patch, HDFS-9079.05.patch, HDFS-9079.06.patch, HDFS-9079.07.patch, HDFS-9079.08.patch, HDFS-9079.09.patch
>
>
> A non-striped DataStreamer goes through the following steps in error handling:
> {code}
> 1) Finds error => 2) Asks NN for new GS => 3) Gets new GS from NN => 4) Applies new GS to DN (createBlockOutputStream) => 5) Ack from DN => 6) Updates block on NN
> {code}
> With multiple streamer threads run in parallel, we need to correctly handle a large number of possible combinations of interleaved thread events. For example, {{streamer_B}} starts step 2 in between events {{streamer_A.2}} and {{streamer_A.3}}.
> HDFS-9040 moves steps 1, 2, 3, 6 from streamer to {{DFSStripedOutputStream}}. This JIRA proposes some further optimizations based on HDFS-9040:
> # We can preallocate GS when NN creates a new striped block group ({{FSN#createNewBlock}}). For each new striped block group we can reserve {{NUM_PARITY_BLOCKS}} GS's. If more than {{NUM_PARITY_BLOCKS}} errors have happened we shouldn't try to further recover anyway.
> # We can use a dedicated event processor to offload the error handling logic from {{DFSStripedOutputStream}}, which is not a long running daemon.
> # We can limit the lifespan of a streamer to be a single block. A streamer ends either after finishing the current block or when encountering a DN failure.
> With the proposed change, a {{StripedDataStreamer}}'s flow becomes:
> {code}
> 1) Finds DN error => 2) Notify coordinator (async, not waiting for response) => terminates
> 1) Finds external error => 2) Applies new GS to DN (createBlockOutputStream) => 3) Ack from DN => 4) Notify coordinator (async, not waiting for response)
> {code}


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