pool: Improve logging for hot file replication

Motivation:

To facilitate debug of user reports regarding hot file replication.

Modification:

- Add enablement information to mover request debug messages.
- Add new debug messages to `MigrationModule.reportFileRequests()` on:

  - NOP due to failure to exceed replication threshold.
  - Discovery of an existing hot file replication job for the same `PnfsId`.

Result:

Improved logging for diagnostic purposes when addressing user reports of
hot file replication issues.

Target: master
Request: 11.2
Patch: https://rb.dcache.org/r/14655/diff/raw
Closes:
Requires-notes: yes
Requires-book: no
Acked-by: Dmitry Litvintsev

Author: greenc-FNAL

modules/dcache/src/main/java/org/dcache/pool/classic/PoolV4.java

@@ -752,8 +752,9 @@ private int queueIoRequest(CellMessage envelope, PoolIoFileMessage message)
     private void ioFile(CellMessage envelope, PoolIoFileMessage message) {
         try {
             message.setMoverId(queueIoRequest(envelope, message));
-            LOGGER.debug("moverId {} received request for pnfsId {}", message.getMoverId(),
-                  message.getPnfsId());
+            LOGGER.debug("moverId {} received request for pnfsId {}, hotfile replication is {}",
+                         message.getMoverId(), message.getPnfsId(), _hotFileReplicationEnabled
+                         ? "enabled" : "disabled");
             if (_hotFileReplicationEnabled) {
                 _fileRequestMonitor.reportFileRequest(message.getPnfsId(),
                       _ioQueue.numberOfRequestsFor(message.getPnfsId()),

modules/dcache/src/main/java/org/dcache/pool/migration/MigrationModule.java

@@ -1252,12 +1252,15 @@ public Object messageArrived(CellMessage envelope, PoolMigrationJobCancelMessage
     public synchronized void reportFileRequest(PnfsId pnfsId, long numberOfRequests,
           ProtocolInfo protocolInfo) {
         if (numberOfRequests < hotFileThreshold) {
+            LOGGER.debug("hotfile replication : conditions not satisfied numberOfRequests {} < hotFileThreshold {}",
+                         numberOfRequests, hotFileThreshold);
             return;
         }
         String jobId = "hotfile-" + pnfsId;
         try {
             Job job = _jobs.get(jobId);
             if (job != null) {
+                LOGGER.debug("hotfile replication : found job with jobid {} in state {}", jobId, job.getState());
                 switch (job.getState()) {
                     case FINISHED:
                     case CANCELLED: