[HDFS-7990] IBR delete ack should not be delayed

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.0-alpha
• Fix Version/s: 2.8.0, 2.7.4, 3.0.0-alpha1
• Component/s: namenode
• Target Version/s: 2.8.0
• Hadoop Flags: Reviewed
• Assignee: Daryn Sharp
• Reporter: Daryn Sharp
• Created: 25/Mar/15 22:09
• Updated: 18/May/17 07:39
• Resolved: 27/Mar/15 14:08

Description

HDFS-395 added the incremental BR feature. A concern was avoiding a race condition with ack-ing block invalidates followed by the directory scanner re-adding the block before the async delete service removes the block, possibly resulting in a full BR that includes the previously delete ack-ed block.

The solution was to batch & delay block deletion acks via a hardcoded interval of 100 * heartbeat interval (default: 5min). The delay isn't required:

1. The FSDatasetSpi tracks blocks pending deletions precisely so the scanner won't re-add the block to the volume map
2. Block receiving, received, and deleted go into the same pending report. A block received event will trigger an immediate IBR which includes the deletion acks. Ie. The delay is meaningless for all but a quiescent cluster
3. Failing to promptly report deleted blocks on a quiescent cluster prevents the NN from updating the block maps to remove the locations

Issue Links

• is depended upon by: HDFS-7967 Reduce the performance impact of the balancer
• is related to: HDFS-11838 Backport HDFS-7990 to branch-2.7: IBR delete ack should not be delayed