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https://issues.apache.org/jira/browse/HBASE-24558?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17135577#comment-17135577
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Pankaj Kumar commented on HBASE-24558:
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Yeah Anoop, we also observed similar problem in our production/test env where
whole cluster nodes were stopped due to power failure or abrupt shutdown.
There were lot many SCPs in the queue as we have limited master proc-thread and
each SCP wait for WAL split & region assignment completion. RS also took long
time in WAL split comparitively as there were huge number of WALs >2k and many
RS would be doing WAL split concurrently, so there will be high load on HDFS.
We tried to tune multiple configuration like,
hbase.master.persist.flushedsequenceid.enabled=true (HBASE-20727)
hbase.split.writer.creation.bounded=true (HBASE-19358)
hbase.regionserver.wal.max.splitters=20
hbase.regionserver.hlog.splitlog.writer.threads=50
Above tunning also MTTR is large time, so we backported HBASE-23286 but it
didn't help much because there were about 4 million revored.hfiles (2000 WALs *
2000 recovered.hfiles ) and that could cause IO overhead (bulkload, compaction).
We did HBase scalability analysis by analyzing HDFS calls through audit log and
profiling HM & RS, observed RS make >15M RPC to HDFS in 10 node cluster which
grows when scaled up. We tried with Observer NameNode but that also didnt help
much.
Currently we are working on reducing the HDFS call in WAL split and making WAL
split and region assignment async in SCP.
> Classic (ZK-based) distributed WAL splitter is inscrutable in operation
> -----------------------------------------------------------------------
>
> Key: HBASE-24558
> URL: https://issues.apache.org/jira/browse/HBASE-24558
> Project: HBase
> Issue Type: Bug
> Components: MTTR
> Reporter: Michael Stack
> Priority: Major
>
> Scenario: decent sized cluster (700 nodes) and WALs backing up (TBD: A
> Replication Peer was in place) such that many RSs had hundreds of WALs. Next,
> a power outage-like event where we have to cold-start. Master comes up and
> files SCPs for old server instances; hundreds. SCP finds there are hundreds
> of WALs and dutifully asks the wal-splitter to do its job. Meantime it goes
> to sleep until completion (See HBASE-24545); no status in log, just loads of
> complaint in log about STUCK procedure worker. Operator sees a stalled master
> dumping into its logs the occasional split completion and STUCK procedures
> but thats it. Operator tries poking up in zk under '/hbase/splitWAL' to see
> whats up but gets a spew back of one-line listing thousands of znodes.
> Operator gets no indication of how we are progressing or of when all is done.
> In my particular case, there were > 100k WALs backed-up. I could dig around
> some and could see that 40k WALs were in-flight at any one time
> (necessitating upping jute.maxbuffer for zk). I could do this:
> {code}$ echo "ls /hbase/splitWAL" | hbase -Djute.maxbuffer=10000000
> org.apache.hadoop.hbase.zookeeper.ZKMainServer | sed -e 's/, /\n/g'|wc{code}
> but it didn't help much as new WALs got added to the backlog. I could do the
> below but it didn't help when WAL count > 100k:
> {code}$ hdfs dfs -lsr /hbase/WALs/*|wc{code}
> Is the count here all the WALs that need splitting (yes, I think). Its less
> than zk count at any one time. How are they tied? Dunno.
> This issue is about improving visibility in our distributed wal-splitter. In
> particular the zk-based splitter visibility is poor (HBASE-21588 is a new
> splitter built on procedures that probably has similar issue). We need to
> have a count of overall outstanding tasks, of how long tasks are taking, and
> of how well distributed the job is (see below).
> An aside was that I had default for {code}HBASE_SPLIT_WAL_MAX_SPLITTER =
> "hbase.regionserver.wal.max.splitters"{code} which is {code}
> public static final int DEFAULT_HBASE_SPLIT_WAL_MAX_SPLITTER = 2; {code} so
> in extremis, I upped the count to 10 but even then looking at random RS's
> they were only getting work on occasion sometimes with hours passing between
> split tasks as though the Master was bad at passing out the jobs: hard to
> tell when no view on what is going on.
> Below is from log of random RS... notice how sporadically it gets split work
> though thousands of WALs to work on:
> {code}
> 89 2020-06-11 04:38:40,113 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@271eba8d
> in 12309ms. Status = DONE
> 90 2020-06-11 04:38:51,445 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@6c9e0b6
> in 13230ms. Status = DONE
> 91 2020-06-11 04:38:57,060 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@7f102aeb
> in 16759ms. Status = DONE
> 92 2020-06-11 09:17:12,762 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@28c31f7d
> in 1181ms. Status = DONE
> 93 2020-06-11 09:17:14,512 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@3ecd4959
> in 2224ms. Status = DONE
> 94 2020-06-11 09:17:14,750 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@5a72b3ad
> in 1345ms. Status = DONE
> 95 2020-06-11 09:17:19,898 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@6af0858d
> in 5319ms. Status = DONE
> 96 2020-06-11 09:17:21,558 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@1bca0d8b
> in 890ms. Status = DONE
> 97 2020-06-11 16:12:31,676 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@50a124bc
> in 1193ms. Status = DONE
> 98 2020-06-11 16:12:34,140 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@519c681c
> in 2383ms. Status = DONE
> 99 2020-06-11 16:12:35,943 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@4a47b062
> in 2278ms. Status = DONE
> 100 2020-06-11 16:12:36,437 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-0] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@f9bcea
> in 1497ms. Status = DONE
> 101 2020-06-11 16:12:39,953 INFO
> [RS_LOG_REPLAY_OPS-regionserver/ps1406:16020-1] handler.WALSplitterHandler:
> Worker ps1406.example.org,16020,1591849310794 done with task
> org.apache.hadoop.hbase.coordination.ZkSplitLogWorkerCoordination$ZkSplitTaskDetails@42d82ac4
> in 914ms. Status = DONE
> {code}
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