Bug: After RegionProcedureStore completes migration of WALProcedureStore, still running WALProcedureStore.syncThread keeps trying to delete now inexistent log files.  
Status: Resolved | Priority: Major | Resolution: Fixed
Created: 15/Jan/20 16:55
Affects Version/s: 3.0.0-alpha-1

With the introduction of the new procedure store to save procs on a table, instead of proc WALs, we added some migration logic to enable a smooth upgrade of clusters under previous versions that used to have proc wal files as the underlying procedure store.

While running a fresh install with latest master branch version, I had noticed that once the old _WALProcedureStore_ directory is detected, it creates and start a WPS instance [here|https://github.com/apache/hbase/blob/master/hbase-server/src/main/java/org/apache/hadoop/hbase/procedure2/store/region/RegionProcedureStore.java#L311], passing a built-in _ProcedureLoader_ [here|https://github.com/apache/hbase/blob/master/hbase-server/src/main/java/org/apache/hadoop/hbase/procedure2/store/region/RegionProcedureStore.java#L315] to perform the conversion from proc wal files to table based.

At the end of this conversion, the builtin loader deletes the proc wal dir [here|https://github.com/apache/hbase/blob/master/hbase-server/src/main/java/org/apache/hadoop/hbase/procedure2/store/region/RegionProcedureStore.java#L363]. This may cause a race condition where a running _WALProcedureStore_ internal thread may be trying to delete the first proc wal file that may had already rolled, then failing with FNFE.

Even worse is that _WALProcedureStore.syncLoop_ keeps trying indefinitely, flooding Master logs with messages such as below:
{noformat}
2020-01-14 06:13:23,331 INFO  [master/hbase01:16000:becomeActiveMaster] region.RegionProcedureStore: The old WALProcedureStore wal directory file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs exists, migrating...
2020-01-14 06:13:23,361 DEBUG [master/hbase01:16000:becomeActiveMaster] wal.WALProcedureStore: Starting WAL Procedure Store lease recovery
2020-01-14 06:13:23,453 INFO  [master/hbase01:16000:becomeActiveMaster] wal.WALProcedureStore: Rolled new Procedure Store WAL, id=1
2020-01-14 06:13:23,454 DEBUG [master/hbase01:16000:becomeActiveMaster] wal.WALProcedureStore: Lease acquired for flushLogId=1
2020-01-14 06:13:23,454 DEBUG [master/hbase01:16000:becomeActiveMaster] wal.WALProcedureStore: No state logs to replay.
2020-01-14 06:13:23,454 INFO  [master/hbase01:16000:becomeActiveMaster] region.RegionProcedureStore: The WALProcedureStore max pid is 0, and the max pid of all loaded procedures is -1
2020-01-14 06:13:23,455 INFO  [master/hbase01:16000:becomeActiveMaster] region.RegionProcedureStore: Migration of WALProcedureStore finished
2020-01-14 06:13:23,455 INFO  [master/hbase01:16000:becomeActiveMaster] procedure2.ProcedureExecutor: Recovered RegionProcedureStore lease in 784 msec
2020-01-14 06:13:23,471 TRACE [WALProcedureStoreSyncThread] wal.WALProcedureStore: no active procedures
2020-01-14 06:13:23,516 INFO  [master/hbase01:16000:becomeActiveMaster] procedure2.ProcedureExecutor: Loaded RegionProcedureStore in 61 msec
2020-01-14 06:13:23,516 INFO  [master/hbase01:16000:becomeActiveMaster] procedure2.RemoteProcedureDispatcher: Instantiated, coreThreads=128 (allowCoreThreadTimeOut=true), queueMaxSize=32, operationDelay=150
2020-01-14 06:13:23,628 INFO  [WALProcedureStoreSyncThread] wal.WALProcedureStore: Rolled new Procedure Store WAL, id=2
2020-01-14 06:13:23,634 INFO  [WALProcedureStoreSyncThread] wal.WALProcedureStore: Remove all state logs with ID less than 1, since no active procedures
2020-01-14 06:13:23,634 TRACE [WALProcedureStoreSyncThread] wal.WALProcedureStore: Removing log=file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log
2020-01-14 06:13:23,634 INFO  [WALProcedureStoreSyncThread] wal.ProcedureWALFile: Archiving file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log to file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/oldWALs/pv2-00000000000000000001.log
2020-01-14 06:13:23,634 ERROR [WALProcedureStoreSyncThread] wal.WALProcedureStore: Unable to remove log: file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log
java.io.FileNotFoundException: File file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log does not exist
...
2020-01-14 06:13:23,635 ERROR [WALProcedureStoreSyncThread] wal.WALProcedureStore: Unable to remove log: file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log
java.io.FileNotFoundException: File file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log does not exist
        at org.apache.hadoop.fs.RawLocalFileSystem.deprecatedGetFileStatus(RawLocalFileSystem.java:635)
...
2020-01-14 06:13:37,352 ERROR [WALProcedureStoreSyncThread] wal.WALProcedureStore: Unable to remove log: file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log
java.io.FileNotFoundException: File file:/root/hbase-3.0.0-SNAPSHOT/hbase-data/MasterProcWALs/pv2-00000000000000000001.log does not exist
        at org.apache.hadoop.fs.RawLocalFileSystem.deprecatedGetFileStatus(RawLocalFileSystem.java:635)
{noformat}
I believe a simple solution in this case is to explicitly call _WALProcedureStore.stop_ method at the end of the migration, which stops _WALProcedureStore_ internal _syncLoop_ thread. 

Am opening a PR soon.