qos: disable dynamic replica reduction

Motivation:
Due to concurrent nature of message processing in dCache data migration
by `migration move` command we might observe a raise condition between PIN
and UNPIN operations, which might be sent and processed in different order.
Thus UNPIN, followed by PIN, with expected result in file being pinned may
be processed as PIN followed by UNPIN, with file ending in unpinned state.

The reduction of pinned replicas on migration event can be skipped. The
redundant pin will be adjusted by scanner on the next run.

Modification:
Skip unpinning if it's not done by scanner.

Result:
no danger in running into raise condition with a cost of redundant
pinned replica for some period of time.

Acked-by: Dmitry Litvintsev
Target: master, 11.0, 10.2, 10.1, 10.0, 9.2
Require-book: no
Require-notes: yes
(cherry picked from commit ef27b1f)
Signed-off-by: Tigran Mkrtchyan <[email protected]>

Author: kofemann

modules/dcache-qos/src/main/java/org/dcache/qos/services/verifier/handlers/FileStatusVerifier.java

@@ -87,6 +87,7 @@ LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 import org.dcache.cells.CellStub;
 import org.dcache.qos.data.FileQoSRequirements;
 import org.dcache.qos.data.QoSAction;
+import org.dcache.qos.data.QoSMessageType;
 import org.dcache.qos.services.verifier.data.PoolInfoMap;
 import org.dcache.qos.services.verifier.data.VerifiedLocations;
 import org.dcache.qos.services.verifier.data.VerifyOperation;
@@ -449,6 +450,18 @@ private Optional<QoSAction> checkForLocationAdjustment(FileQoSRequirements requi
             }
         }
 
+        // REVISIT: effectively disable adjustment if we need to reduce the number of replicas.
+        //
+        // This section is added due to race condition between PIN and UNPIN operations, which
+        // may lead to PIN and UNPIN requests processed out of order. Thus UNPIN, followed by PIN, with
+        // expected result in file being pinned may be processed as PIN followed by UNPIN, with
+        // file ending in unpinned state.
+        //
+         // The redundant pinned copy will be reduced by scanner at the next run.
+        if (missing < 0 && operation.getMessageType() != QoSMessageType.SYSTEM_SCAN) {
+            missing = 0;
+        }
+
         operation.setNeeded(Math.abs(missing));
 
         LOGGER.debug("{}, checkForLocationAdjustment; required {}, excluded {}, missing {}.",