[HBASE-1876] DroppedSnapshotException when flushing memstore after a datanode dies

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.20.0
• Fix Version/s: 0.90.0
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Cosmin Lehene
• Reporter: Cosmin Lehene
• Created: 30/Sep/09 16:48
• Updated: 20/Nov/15 13:02
• Resolved: 17/Jul/10 15:38

Description

A dead datanode in the cluster can lead to multiple HRegionServer failures and corrupted data. The HRegionServer failures can be reproduced consistently on a 7 machines cluster with approx 2000 regions.

Steps to reproduce

The easiest and safest way is to reproduce it for the .META. table, however it will work with any table.

Locate a datanode that stores the .META. files and kill -9 it.
In order to get multiple writes to the .META. table bring up or shut down a region server this will eventually cause a flush on the memstore

2009-09-25 09:26:17,775 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Flush requested on .META.,demo__assets,asset_283132172,1252898166036,1253265069920
2009-09-25 09:26:17,775 DEBUG org.apache.hadoop.hbase.regionserver.HRegion: Started memstore flush for region .META.,demo__assets,asset_283132172,1252898166036,1253265069920. Current region memstore si
ze 16.3k
2009-09-25 09:26:17,791 INFO org.apache.hadoop.hdfs.DFSClient: Exception in createBlockOutputStream java.io.IOException: Bad connect ack with firstBadLink 10.72.79.108:50010
2009-09-25 09:26:17,791 INFO org.apache.hadoop.hdfs.DFSClient: Abandoning block blk_-8767099282771605606_176852

The DFSClient will retry for 3 times, but there's a high chance it will try on the same failed datanode (it takes around 10 minutes for dead datanode to be removed from cluster)

2009-09-25 09:26:41,810 WARN org.apache.hadoop.hdfs.DFSClient: DataStreamer Exception: java.io.IOException: Unable to create new block.
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2814)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2078)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2264)

2009-09-25 09:26:41,810 WARN org.apache.hadoop.hdfs.DFSClient: Error Recovery for block blk_5317304716016587434_176852 bad datanode[2] nodes == null
2009-09-25 09:26:41,810 WARN org.apache.hadoop.hdfs.DFSClient: Could not get block locations. Source file "/hbase/.META./225980069/info/5573114819456511457" - Aborting...
2009-09-25 09:26:41,810 FATAL org.apache.hadoop.hbase.regionserver.MemStoreFlusher: Replay of hlog required. Forcing server shutdown
org.apache.hadoop.hbase.DroppedSnapshotException: region: .META.,demo__assets,asset_283132172,1252898166036,1253265069920
at org.apache.hadoop.hbase.regionserver.HRegion.internalFlushcache(HRegion.java:942)
at org.apache.hadoop.hbase.regionserver.HRegion.flushcache(HRegion.java:835)
at org.apache.hadoop.hbase.regionserver.MemStoreFlusher.flushRegion(MemStoreFlusher.java:241)
at org.apache.hadoop.hbase.regionserver.MemStoreFlusher.run(MemStoreFlusher.java:149)
Caused by: java.io.IOException: Bad connect ack with firstBadLink 10.72.79.108:50010
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.createBlockOutputStream(DFSClient.java:2872)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:2795)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2000(DFSClient.java:2078)
at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:2264)

After the HRegionServer shuts down itself the regions will be reassigned however you might hit this

2009-09-26 08:04:23,646 INFO org.apache.hadoop.hbase.regionserver.HRegionServer: Worker: MSG_REGION_OPEN: .META.,demo__assets,asset_283132172,1252898166036,1253265069920
2009-09-26 08:04:23,684 WARN org.apache.hadoop.hbase.regionserver.Store: Skipping hdfs://b0:9000/hbase/.META./225980069/historian/1432202951743803786 because its empty. HBASE-646 DATA LOSS?
...
2009-09-26 08:04:23,776 INFO org.apache.hadoop.hbase.regionserver.HRegion: region .META.,demo__assets,asset_283132172,1252898166036,1253265069920/225980069 available; sequence id is 1331458484

We ended up with corrupted data in .META. "info:server" after master got confirmation that it was updated from the HRegionServer that got DroppedSnapshotException

Since after a cluster restart server:info will be correct, .META. is safer to test with. Also to detect data corruption you can just scan .META. get the start key for each region and attempt to retrieve it from the corresponding table. If .META. is corrupted you get a NotServingRegionException.

This issue is related to https://issues.apache.org/jira/browse/HDFS-630

I attached a patch for HDFS-630 https://issues.apache.org/jira/secure/attachment/12420919/HDFS-630.patch that fixes this problem.

Issue Links

• is blocked by: HDFS-630 In DFSOutputStream.nextBlockOutputStream(), the client can exclude specific datanodes when locating the next block.