[HDFS-4350] Make enabling of stale marking on read and write paths independent - ASF JIRA

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Details

Type: Bug
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: 3.0.0-alpha1
Fix Version/s: 1.2.0, 2.0.3-alpha
Component/s: None
Labels:
None

Target Version/s:

1.2.0, 2.0.3-alpha
Hadoop Flags:

Incompatible change, Reviewed
Release Note:

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This patch makes an incompatible configuration change, as described below:
In releases 1.1.0 and other point releases 1.1.x, the configuration parameter "dfs.namenode.check.stale.datanode" could be used to turn on checking for the stale nodes. This configuration is no longer supported in release 1.2.0 onwards and is renamed as "dfs.namenode.avoid.read.stale.datanode".

How feature works and configuring this feature:
As described in ~~HDFS-3703~~ release notes, datanode stale period can be configured using parameter "dfs.namenode.stale.datanode.interval" in seconds (default value is 30 seconds). NameNode can be configured to use this staleness information for reads using configuration "dfs.namenode.avoid.read.stale.datanode". When this parameter is set to true, namenode picks a stale datanode as the last target to read from when returning block locations for reads. Using staleness information for writes is as described in the releases notes of ~~HDFS-3912~~.

Show
This patch makes an incompatible configuration change, as described below: In releases 1.1.0 and other point releases 1.1.x, the configuration parameter "dfs.namenode.check.stale.datanode" could be used to turn on checking for the stale nodes. This configuration is no longer supported in release 1.2.0 onwards and is renamed as "dfs.namenode.avoid.read.stale.datanode". How feature works and configuring this feature: As described in HDFS-3703 release notes, datanode stale period can be configured using parameter "dfs.namenode.stale.datanode.interval" in seconds (default value is 30 seconds). NameNode can be configured to use this staleness information for reads using configuration "dfs.namenode.avoid.read.stale.datanode". When this parameter is set to true, namenode picks a stale datanode as the last target to read from when returning block locations for reads. Using staleness information for writes is as described in the releases notes of HDFS-3912 .

Description

Marking of datanodes as stale for the read and write path was introduced in ~~HDFS-3703~~ and ~~HDFS-3912~~ respectively. This is enabled using two new keys, DFS_NAMENODE_CHECK_STALE_DATANODE_KEY and DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_WRITE_KEY. However, there currently exists a dependency, since you cannot enable write marking without also enabling read marking, since the first key enables both checking of staleness and read marking.

I propose renaming the first key to DFS_NAMENODE_AVOID_STALE_DATANODE_FOR_READ_KEY, and make checking enabled if either of the keys are set. This will allow read and write marking to be enabled independently.