[HDFS-2709] HA: Appropriately handle error conditions in EditLogTailer

• Type: Sub-task
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: HA branch (HDFS-1623)
• Fix Version/s: HA branch (HDFS-1623)
• Component/s: ha, namenode
• Target Version/s: HA branch (HDFS-1623)
• Hadoop Flags: Reviewed
• Assignee: Aaron Myers
• Reporter: Todd Lipcon
• Created: 20/Dec/11 22:50
• Updated: 16/May/12 06:57
• Resolved: 06/Jan/12 20:44

Description

Currently if the edit log tailer experiences an error replaying edits in the middle of a file, it will go back to retrying from the beginning of the file on the next tailing iteration. This is incorrect since many of the edits will have already been replayed, and not all edits are idempotent.

Instead, we either need to (a) support reading from the middle of a finalized file (ie skip those edits already applied), or (b) abort the standby if it hits an error while tailing. If "a" isn't simple, let's do "b" for now and come back to 'a' later since this is a rare circumstance and better to abort than be incorrect.

Issue Links

• relates to: HDFS-2759 Pre-allocate HDFS edit log files after writing version number