HBASE-21721 reduce write#syncs() times (apache#2220)

Signed-off-by: Anoop <anoopsamjohn@apache.org>
Signed-off-by: stack <stack@apache.org>

Author: cuibo01

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/FSHLog.java

@@ -1006,7 +1006,7 @@ public Path getCurrentFileName() {
   public long getFilenum() {
     return filenum.get();
   }
-  
+
   @Override
   public String toString() {
     return "FSHLog " + logFilePrefix + ":" + logFileSuffix + "(num " + filenum + ")";
@@ -1283,8 +1283,12 @@ public void run() {
           Throwable lastException = null;
           try {
             Trace.addTimelineAnnotation("syncing writer");
+            long unSyncedFlushSeq = highestUnsyncedSequence;
             writer.sync();
             Trace.addTimelineAnnotation("writer synced");
+            if (unSyncedFlushSeq > currentSequence) {
+              currentSequence = unSyncedFlushSeq;
+            }
             currentSequence = updateHighestSyncedSequence(currentSequence);
           } catch (IOException e) {
             LOG.error("Error syncing, request close of WAL", e);