[jira] [Created] (HBASE-25924) Seeing a spike in uncleanlyClosedWALs metric.

["Rushabh Shah (Jira)" <ji...@apache.org>]

Rushabh Shah created HBASE-25924:
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             Summary: Seeing a spike in uncleanlyClosedWALs metric.
                 Key: HBASE-25924
                 URL: https://issues.apache.org/jira/browse/HBASE-25924
             Project: HBase
          Issue Type: Bug
            Reporter: Rushabh Shah
            Assignee: Rushabh Shah


Getting the following log line in all of our production clusters when WALEntryStream is dequeuing WAL file.

{noformat}
 2021-05-02 04:01:30,437 DEBUG [04901996] regionserver.WALEntryStream - Reached the end of WAL file hdfs://<wal-file-name>. It was not closed cleanly, so we did not parse 8 bytes of data. This is normally ok.
{noformat}
The 8 bytes are usually the trailer size.

While dequeue'ing the WAL file from WALEntryStream, we reset the reader here.
[WALEntryStream|https://github.com/apache/hbase/blob/branch-1/hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/WALEntryStream.java#L199-L221]

{code:java}
  private void tryAdvanceEntry() throws IOException {
    if (checkReader()) {
      readNextEntryAndSetPosition();
      if (currentEntry == null) { // no more entries in this log file - see if log was rolled
        if (logQueue.getQueue(walGroupId).size() > 1) { // log was rolled
          // Before dequeueing, we should always get one more attempt at reading.
          // This is in case more entries came in after we opened the reader,
          // and a new log was enqueued while we were reading. See HBASE-6758
          resetReader(); ---> HERE
          readNextEntryAndSetPosition();
          if (currentEntry == null) {
            if (checkAllBytesParsed()) { // now we're certain we're done with this log file
              dequeueCurrentLog();
              if (openNextLog()) {
                readNextEntryAndSetPosition();
              }
            }
          }
        } // no other logs, we've simply hit the end of the current open log. Do nothing
      }
    }
    // do nothing if we don't have a WAL Reader (e.g. if there's no logs in queue)
  }
{code}

In resetReader, we call the following methods, WALEntryStream#resetReader  ---->  ProtobufLogReader#reset ---> ProtobufLogReader#initInternal.
In ProtobufLogReader#initInternal, we try to create the whole reader object from scratch to see if any new data has been written.
We reset all the fields of ProtobufLogReader except for ReaderBase#fileLength.
We calculate whether trailer is present or not depending on fileLength.



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