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https://issues.apache.org/jira/browse/HDFS-12665?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16217962#comment-16217962
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Virajith Jalaparti commented on HDFS-12665:
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bq. Sure. This means all the classes used by fs2img will be in the same package
(unless they need dependencies like using DynamoDB, AzureTable, etc).
Yes, HDFS-11902 already includes this change.
bq. In an early version we refactored it to use ExtendedBlock as the key but
were advised that it should remain Block. AIUI, the AliasMap is unique to a NN
so there is no ambiguity.
Yes, only one NN uses the AliasMap. However, the check was on the DN to ensure
that when using HDFS federation (multiple block pool ids), the provided volume
wasn't report to the NN which doesn't expect the blocks to be reported.
bq. If an administrator is running with
{{DFSConfigKeys.DFS_NAMENODE_PROVIDED_ENABLED}} set to false but
{{DFSConfigKeys.DFS_USE_ALIASMAP}} set to true, it's pretty lame. Should we
throw or just log a warning about the misconfiguration
I think logging a warning and disabling this makes sense.
> [AliasMap] Create a version of the AliasMap that runs in memory in the
> Namenode (leveldb)
> -----------------------------------------------------------------------------------------
>
> Key: HDFS-12665
> URL: https://issues.apache.org/jira/browse/HDFS-12665
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Ewan Higgs
> Assignee: Ewan Higgs
> Attachments: HDFS-12665-HDFS-9806.001.patch,
> HDFS-12665-HDFS-9806.002.patch
>
>
> The design of Provided Storage requires the use of an AliasMap to manage the
> mapping between blocks of files on the local HDFS and ranges of files on a
> remote storage system. To reduce load from the Namenode, this can be done
> using a pluggable external service (e.g. AzureTable, Cassandra, Ratis).
> However, to aide adoption and ease of deployment, we propose an in memory
> version.
> This AliasMap will be a wrapper around LevelDB (already a dependency from the
> Timeline Service) and use protobuf for the key (blockpool, blockid, and
> genstamp) and the value (url, offset, length, nonce). The in memory service
> will also have a configurable port on which it will listen for updates from
> Storage Policy Satisfier (SPS) Coordinating Datanodes (C-DN).
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