[HDFS-12594] snapshotDiff fails if the report exceeds the RPC response limit

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.1.0
• Component/s: hdfs
• Hadoop Flags: Reviewed
• Assignee: Shashikant Banerjee
• Reporter: Shashikant Banerjee
• Created: 05/Oct/17 13:32
• Updated: 02/Oct/18 22:22
• Resolved: 30/Nov/17 20:22

Description

The snapshotDiff command fails if the snapshotDiff report size is larger than the configuration value of ipc.maximum.response.length which is by default 128 MB.

Worst case, with all Renames ops in sanpshots each with source and target name equal to MAX_PATH_LEN which is 8k characters, this would result in at 8192 renames.

SnapshotDiff is currently used by distcp to optimize copy operations and in case of the the diff report exceeding the limit , it fails with the below exception:

Test set: org.apache.hadoop.hdfs.server.namenode.snapshot.TestSnapshotDiffReport
-------------------------------------------------------------------------------
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 112.095 sec <<< FAILURE! - in org.apache.hadoop.hdfs.server.namenode.snapshot.TestSnapshotDiffReport
testDiffReportWithMillionFiles(org.apache.hadoop.hdfs.server.namenode.snapshot.TestSnapshotDiffReport) Time elapsed: 111.906 sec <<< ERROR!
java.io.IOException: Failed on local exception: org.apache.hadoop.ipc.RpcException: RPC response exceeds maximum data length; Host Details : local host is: "hw15685.local/10.200.5.230"; destination host is: "localhost":59808;

Attached is the proposal for the changes required.

Issue Links

• is related to: HDFS-12165 getSnapshotDiffReport throws NegativeArraySizeException for very large snapshot diff summary
• relates to: HDFS-13143 SnapshotDiff - snapshotDiffReport might be inconsistent if the snapshotDiff calculation happens between a snapshot and the current tree