[HDFS-11565] Use compact identifiers for built-in ECPolicies in HdfsFileStatus

• Type: Improvement
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 3.0.0-alpha2
• Fix Version/s: 3.0.0-alpha4
• Component/s: erasure-coding
• Labels: hdfs-ec-3.0-must-do
• Target Version/s: 3.0.0-alpha4
• Hadoop Flags: Incompatible change
• Release Note: Some of the existing fields in ErasureCodingPolicyProto have changed from required to optional. For system EC policies, these fields are populated from hardcoded values.
• Assignee: Andrew Wang
• Reporter: Andrew Wang
• Created: 22/Mar/17 23:45
• Updated: 18/Oct/17 22:53
• Resolved: 12/Apr/17 19:25

Description

Discussed briefly on HDFS-7337 with Kai Zheng. Quoting our convo:

From looking at the protos, one other question I had is about the overhead of these protos when using the hardcoded policies. There are a bunch of strings and ints, which can be kind of heavy since they're added to each HdfsFileStatus. Should we make the built-in ones identified by purely an ID, with these fully specified protos used for the pluggable policies?

Sounds like this could be considered separately because, either built-in policies or plugged-in polices, the full meta info is maintained either by the codes or in the fsimage persisted, so identifying them by purely an ID should works fine. If agree, we could refactor the codes you mentioned above separately.

Issue Links

• depends upon: HDFS-11623 Move system erasure coding policies into hadoop-hdfs-client
• is related to: HDFS-12682 ECAdmin -listPolicies will always show SystemErasureCodingPolicies state as DISABLED