[HBASE-10499] In write heavy scenario one of the regions does not get flushed causing RegionTooBusyException

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.98.0
• Fix Version/s: 1.0.0, 0.98.10, 1.1.0
• Hadoop Flags: Reviewed
• Assignee: Ted Yu
• Reporter: ramkrishna.s.vasudevan
• Created: 11/Feb/14 12:00
• Updated: 06/Apr/18 17:55
• Resolved: 23/Jan/15 21:58

Description

I got this while testing 0.98RC. But am not sure if it is specific to this version. Doesn't seem so to me.
Also it is something similar to HBASE-5312 and HBASE-5568.

Using 10 threads i do writes to 4 RS using YCSB. The table created has 200 regions. In one of the run with 0.98 server and 0.98 client I faced this problem like the hlogs became more and the system requested flushes for those many regions.
One by one everything was flushed except one and that one thing remained unflushed. The ripple effect of this on the client side

com.yahoo.ycsb.DBException: org.apache.hadoop.hbase.client.RetriesExhaustedWithDetailsException: Failed 54 actions: RegionTooBusyException: 54 times,
        at com.yahoo.ycsb.db.HBaseClient.cleanup(HBaseClient.java:245)
        at com.yahoo.ycsb.DBWrapper.cleanup(DBWrapper.java:73)
        at com.yahoo.ycsb.ClientThread.run(Client.java:307)
Caused by: org.apache.hadoop.hbase.client.RetriesExhaustedWithDetailsException: Failed 54 actions: RegionTooBusyException: 54 times,
        at org.apache.hadoop.hbase.client.AsyncProcess$BatchErrors.makeException(AsyncProcess.java:187)
        at org.apache.hadoop.hbase.client.AsyncProcess$BatchErrors.access$500(AsyncProcess.java:171)
        at org.apache.hadoop.hbase.client.AsyncProcess.getErrors(AsyncProcess.java:897)
        at org.apache.hadoop.hbase.client.HTable.backgroundFlushCommits(HTable.java:961)
        at org.apache.hadoop.hbase.client.HTable.flushCommits(HTable.java:1225)
        at com.yahoo.ycsb.db.HBaseClient.cleanup(HBaseClient.java:232)
        ... 2 more

On one of the RS

2014-02-11 08:45:58,714 INFO  [regionserver60020.logRoller] wal.FSHLog: Too many hlogs: logs=38, maxlogs=32; forcing flush of 23 regions(s): 97d8ae2f78910cc5ded5fbb1ddad8492, d396b8a1da05c871edcb68a15608fdf2, 01a68742a1be3a9705d574ad68fec1d7, 1250381046301e7465b6cf398759378e, 127c133f47d0419bd5ab66675aff76d4, 9f01c5d25ddc6675f750968873721253, 29c055b5690839c2fa357cd8e871741e, ca4e33e3eb0d5f8314ff9a870fc43463, acfc6ae756e193b58d956cb71ccf0aa3, 187ea304069bc2a3c825bc10a59c7e84, 0ea411edc32d5c924d04bf126fa52d1e, e2f9331fc7208b1b230a24045f3c869e, d9309ca864055eddf766a330352efc7a, 1a71bdf457288d449050141b5ff00c69, 0ba9089db28e977f86a27f90bbab9717, fdbb3242d3b673bbe4790a47bc30576f, bbadaa1f0e62d8a8650080b824187850, b1a5de30d8603bd5d9022e09c574501b, cc6a9fabe44347ed65e7c325faa72030, 313b17dbff2497f5041b57fe13fa651e, 6b788c498503ddd3e1433a4cd3fb4e39, 3d71274fe4f815882e9626e1cfa050d1, acc43e4b42c1a041078774f4f20a3ff5
......................................................
2014-02-11 08:47:49,580 INFO  [regionserver60020.logRoller] wal.FSHLog: Too many hlogs: logs=53, maxlogs=32; forcing flush of 2 regions(s): fdbb3242d3b673bbe4790a47bc30576f, 6b788c498503ddd3e1433a4cd3fb4e39

2014-02-11 09:42:44,237 INFO  [regionserver60020.periodicFlusher] regionserver.HRegionServer: regionserver60020.periodicFlusher requesting flush for region usertable,user3654,1392107806977.fdbb3242d3b673bbe4790a47bc30576f. after a delay of 16689
2014-02-11 09:42:44,237 INFO  [regionserver60020.periodicFlusher] regionserver.HRegionServer: regionserver60020.periodicFlusher requesting flush for region usertable,user6264,1392107806983.6b788c498503ddd3e1433a4cd3fb4e39. after a delay of 15868
2014-02-11 09:42:54,238 INFO  [regionserver60020.periodicFlusher] regionserver.HRegionServer: regionserver60020.periodicFlusher requesting flush for region usertable,user3654,1392107806977.fdbb3242d3b673bbe4790a47bc30576f. after a delay of 20847
2014-02-11 09:42:54,238 INFO  [regionserver60020.periodicFlusher] regionserver.HRegionServer: regionserver60020.periodicFlusher requesting flush for region usertable,user6264,1392107806983.6b788c498503ddd3e1433a4cd3fb4e39. after a delay of 20099
2014-02-11 09:43:04,238 INFO  [regionserver60020.periodicFlusher] regionserver.HRegionServer: regionserver60020.periodicFlusher requesting flush for region usertable,user3654,1392107806977.fdbb3242d3b673bbe4790a47bc30576f. after a delay of 8677

2014-02-11 10:31:21,020 INFO  [regionserver60020.logRoller] wal.FSHLog: Too many hlogs: logs=54, maxlogs=32; forcing flush of 1 regions(s): fdbb3242d3b673bbe4790a47bc30576f

I restarted another RS and there were region movements with other regions but this region stays with the RS that has this issue. One important observation is that in HRegion.internalflushCache() we need to add a debug log here

// If nothing to flush, return and avoid logging start/stop flush.
    if (this.memstoreSize.get() <= 0) {
      return false;
    }

Because we can see that the region is requsted for a flush but it does not happen and no logs related to flush are printed in the logs. so due to some reason this memstore.size() has become 0( I assume this). The earlier bugs were also due to similar reason.