cta/CTA#777 Minimize mounts for dual copy tape pool recalls

A temporary fix that tries to force recalls to use the
tape copies with the lowest tape copy numbers.

scheduler/Scheduler.cpp

@@ -193,6 +193,42 @@ std::string Scheduler::queueRetrieve(
   common::dataStructures::RetrieveFileQueueCriteria queueCriteria;
   queueCriteria = m_catalogue.prepareToRetrieveFile(instanceName, request.archiveFileID, request.requester, request.activity, lc);
   queueCriteria.archiveFile.diskFileInfo = request.diskFileInfo;
+
+  // The following if statement is a temporary fix for the following CTA issue:
+  //
+  //   cta/CTA#777 Minimize mounts for dual copy tape pool recalls
+  //
+  // The code tries to force a recall to use the tape copy with the lowest
+  // tape copy number.  On the one hand this increases wear and tear on tapes
+  // containing files with lower tape copy numbers but on the other hand it
+  // reduces the number of overall number tape mounts in situations where files
+  // with multiple tape copies are being recalled.
+  if (1 < queueCriteria.archiveFile.tapeFiles.size()) {
+    uint8_t lowestCopyNb = std::numeric_limits<uint8_t>::max();
+    std::map<uint8_t, common::dataStructures::TapeFile> copyNbToTapeFile;
+    for (auto tapeFile: queueCriteria.archiveFile.tapeFiles) {
+      if (copyNbToTapeFile.end() == copyNbToTapeFile.find(tapeFile.copyNb)) {
+        if (tapeFile.copyNb < lowestCopyNb) {
+          lowestCopyNb = tapeFile.copyNb;
+        }
+        copyNbToTapeFile[tapeFile.copyNb] = tapeFile;
+      } else {
+        std::ostringstream msg;
+        msg << __FUNCTION__ << ": Found archive file with duplicate tape copy number: vid=" << tapeFile.vid <<
+            " copyNb=" << (uint32_t)tapeFile.copyNb;
+        lc.log(log::WARNING, msg.str());
+      }
+    }
+
+    if (!copyNbToTapeFile.empty()) {
+      const auto lowestCopyNbTapeFile = copyNbToTapeFile.find(lowestCopyNb);
+      if (copyNbToTapeFile.end() != lowestCopyNbTapeFile) {
+        queueCriteria.archiveFile.tapeFiles.clear();
+        queueCriteria.archiveFile.tapeFiles.push_back(lowestCopyNbTapeFile->second);
+      }
+    }
+  }
+
   auto diskSystemList = m_catalogue.getAllDiskSystems();
   auto catalogueTime = t.secs(cta::utils::Timer::resetCounter);
   // By default, the scheduler makes its decision based on all available vids. But if a vid is specified in the protobuf,