[jira] [Created] (HBASE-21544) WAL writer for recovered.edits file in WalSplitting should not require hflush from filesystem

["Josh Elser (JIRA)" <ji...@apache.org>]

Josh Elser created HBASE-21544:
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             Summary: WAL writer for recovered.edits file in WalSplitting should not require hflush from filesystem
                 Key: HBASE-21544
                 URL: https://issues.apache.org/jira/browse/HBASE-21544
             Project: HBase
          Issue Type: Bug
          Components: wal
            Reporter: Josh Elser
            Assignee: Josh Elser
             Fix For: 3.0.0, 2.2.0, 2.1.2, 2.0.4


Been talking through this with a bunch of folks. [~enis] brought me back from the cliff of despair though.

Context: running HBase on top of a filesystem that doesn't have hflush for hfiles. In our case, on top of Azure's Hadoop-compatible filesystems (WASB, ABFS).

When a RS fails and we have an SCP running for it, you'll see log splitting get into an "infinite" loop where the master keeps resubmitting and the RS which takes the action deterministically fails with the following:
{noformat}
2018-11-26 20:59:18,415 ERROR [RS_LOG_REPLAY_OPS-regionserver/wn2-b831f9:16020-0-Writer-2] wal.FSHLogProvider: The RegionServer write ahead log provider for FileSystem implementations relies on the ability to call hflush for proper operation during component failures, but the current FileSystem does not support doing so. Please check the config value of 'hbase.wal.dir' and ensure it points to a FileSystem mount that has suitable capabilities for output streams.
2018-11-26 20:59:18,415 WARN  [RS_LOG_REPLAY_OPS-regionserver/wn2-b831f9:16020-0-Writer-2] wal.AbstractProtobufLogWriter: WALTrailer is null. Continuing with default.
2018-11-26 20:59:18,467 ERROR [RS_LOG_REPLAY_OPS-regionserver/wn2-b831f9:16020-0-Writer-2] wal.WALSplitter: Got while writing log entry to log
java.io.IOException: cannot get log writer
        at org.apache.hadoop.hbase.wal.FSHLogProvider.createWriter(FSHLogProvider.java:96)
        at org.apache.hadoop.hbase.wal.FSHLogProvider.createWriter(FSHLogProvider.java:61)
        at org.apache.hadoop.hbase.wal.WALFactory.createRecoveredEditsWriter(WALFactory.java:370)
        at org.apache.hadoop.hbase.wal.WALSplitter.createWriter(WALSplitter.java:804)
        at org.apache.hadoop.hbase.wal.WALSplitter$LogRecoveredEditsOutputSink.createWAP(WALSplitter.java:1530)
        at org.apache.hadoop.hbase.wal.WALSplitter$LogRecoveredEditsOutputSink.getWriterAndPath(WALSplitter.java:1501)
        at org.apache.hadoop.hbase.wal.WALSplitter$LogRecoveredEditsOutputSink.appendBuffer(WALSplitter.java:1584)
        at org.apache.hadoop.hbase.wal.WALSplitter$LogRecoveredEditsOutputSink.append(WALSplitter.java:1566)
        at org.apache.hadoop.hbase.wal.WALSplitter$WriterThread.writeBuffer(WALSplitter.java:1090)
        at org.apache.hadoop.hbase.wal.WALSplitter$WriterThread.doRun(WALSplitter.java:1082)
        at org.apache.hadoop.hbase.wal.WALSplitter$WriterThread.run(WALSplitter.java:1052)
Caused by: org.apache.hadoop.hbase.util.CommonFSUtils$StreamLacksCapabilityException: hflush
        at org.apache.hadoop.hbase.regionserver.wal.ProtobufLogWriter.initOutput(ProtobufLogWriter.java:99)
        at org.apache.hadoop.hbase.regionserver.wal.AbstractProtobufLogWriter.init(AbstractProtobufLogWriter.java:165)
        at org.apache.hadoop.hbase.wal.FSHLogProvider.createWriter(FSHLogProvider.java:77)
        ... 10 more{noformat}
This is the sanity check added by HBASE-18784, failing on creating the writer for the recovered.edits file.

The odd-ball here is that our recovered.edits writer is just a WAL writer class. The WAL writer class thinks it always should have hflush support; however, we don't _actually_ need that for writing out the recovered.edits files. If {{close()}} on the recovered.edits file would fail, we're trash any intermediate data in the filesystem and rerun the whole process.

It's my understanding that this check is over-bearing and we should not make the check when the ProtobufLogWriter is being used for the recovered.edits file.

[~zyork], [~busbey] fyi



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