SERVER-71792 Log list of cursors a range deletion is going to wait on

4 files changed, 79 insertions, 0 deletions

diff --git a/src/mongo/db/cursor_manager.cpp b/src/mongo/db/cursor_manager.cpp
index 214c1c2bf3f..eb2e3dad8bb 100644
--- a/src/mongo/db/cursor_manager.cpp
+++ b/src/mongo/db/cursor_manager.cpp
@@ -186,6 +186,24 @@ std::size_t CursorManager::timeoutCursors(OperationContext* opCtx, Date_t now) {
     return toDisposeWithoutMutex.size();
 }
 
+std::vector<CursorId> CursorManager::getCursorIdsForNamespace(const NamespaceString& nss) {
+    std::vector<CursorId> cursorIds;
+
+    // Lock and inspect one partition at a time in order to avoid contention. It is acceptable for
+    // the output not to include info about cursors opened/closed while iterating.
+    for (size_t partitionId = 0; partitionId < kNumPartitions; ++partitionId) {
+        auto lockedPartition = _cursorMap->lockOnePartitionById(partitionId);
+        for (auto it = lockedPartition->begin(); it != lockedPartition->end(); ++it) {
+            auto* cursor = it->second;
+            if (cursor->nss() == nss) {
+                cursorIds.push_back(cursor->cursorid());
+            }
+        }
+    }
+
+    return cursorIds;
+}
+
 StatusWith<ClientCursorPin> CursorManager::pinCursor(
     OperationContext* opCtx,
     CursorId id,
diff --git a/src/mongo/db/cursor_manager.h b/src/mongo/db/cursor_manager.h
index bce3b05fdea..ed5cdb4e876 100644
--- a/src/mongo/db/cursor_manager.h
+++ b/src/mongo/db/cursor_manager.h
@@ -194,6 +194,17 @@ public:
                                                            const SessionKiller::Matcher& matcher);
 
     /**
+     * Returns a vector of open cursor ids registered on the `nss`. The result doesn't include
+     * cursors registered for a different namespace but also acting on `nss` (e.g. in presence of
+     * sub-pipelines).
+     *
+     * Locks/inspects one partition at a time, hence the result might not include new cursors being
+     * opened on the namespace. The only guarantee is that the result will include any cursor opened
+     * before calling this method and not closed before iterating the partition holding it.
+     */
+    std::vector<CursorId> getCursorIdsForNamespace(const NamespaceString& nss);
+
+    /**
      * Set the CursorManager's ClockSource*.
      */
     void setPreciseClockSource(ClockSource* preciseClockSource) {
diff --git a/src/mongo/db/s/range_deleter_service_op_observer.cpp b/src/mongo/db/s/range_deleter_service_op_observer.cpp
index 7c0d0084963..93de39a2377 100644
--- a/src/mongo/db/s/range_deleter_service_op_observer.cpp
+++ b/src/mongo/db/s/range_deleter_service_op_observer.cpp
@@ -30,6 +30,7 @@
 #include "mongo/db/s/range_deleter_service_op_observer.h"
 
 #include "mongo/db/catalog_raii.h"
+#include "mongo/db/cursor_manager.h"
 #include "mongo/db/persistent_task_store.h"
 #include "mongo/db/s/collection_sharding_runtime.h"
 #include "mongo/db/s/range_deleter_service.h"
@@ -54,6 +55,16 @@ void registerTaskWithOngoingQueriesOnOpLogEntryCommit(OperationContext* opCtx,
                                                                                   rdt.getNss())
                     ->getOngoingQueriesCompletionFuture(rdt.getCollectionUuid(), rdt.getRange())
                     .semi();
+            if (!waitForActiveQueriesToComplete.isReady()) {
+                const auto openCursorsIds =
+                    CursorManager::get(opCtx)->getCursorIdsForNamespace(rdt.getNss());
+                LOGV2_INFO(
+                    7179200,
+                    "Range deletion will be scheduled after all possibly dependent queries finish",
+                    "namespace"_attr = rdt.getNss(),
+                    "range"_attr = rdt.getRange(),
+                    "cursorsDirectlyReferringTheNamespace"_attr = openCursorsIds);
+            }
             (void)RangeDeleterService::get(opCtx)->registerTask(
                 rdt, std::move(waitForActiveQueriesToComplete));
         } catch (const DBException& ex) {
diff --git a/src/mongo/dbtests/cursor_manager_test.cpp b/src/mongo/dbtests/cursor_manager_test.cpp
index fa85089ff26..61845775695 100644
--- a/src/mongo/dbtests/cursor_manager_test.cpp
+++ b/src/mongo/dbtests/cursor_manager_test.cpp
@@ -754,5 +754,44 @@ TEST_F(CursorManagerTestCustomOpCtx, CursorsMarkedAsKilledAreReturnedForOpKeyLoo
     auto cursors = useCursorManager()->getCursorsForOpKeys({opKey});
     ASSERT_EQ(cursors.size(), size_t(1));
 }
+
+TEST_F(CursorManagerTestCustomOpCtx,
+       GetCursorIdsForNamespaceReturnsSingleEntryForMatchingNamespace) {
+    auto opCtx = _queryServiceContext->makeOperationContext();
+    auto pinned = makeCursor(opCtx.get());
+    auto cursorId = pinned.getCursor()->cursorid();
+    auto cursorsForNamespace = useCursorManager()->getCursorIdsForNamespace(kTestNss);
+    ASSERT_EQUALS(cursorsForNamespace.size(), 1ull);
+    ASSERT_EQUALS(cursorsForNamespace[0], cursorId);
+}
+
+TEST_F(CursorManagerTestCustomOpCtx,
+       GetCursorIdsForNamespaceReturnsMultipleEntriesForMatchingNamespace) {
+    auto opCtx = _queryServiceContext->makeOperationContext();
+    auto pinned1 = makeCursor(opCtx.get());
+    auto pinned2 = makeCursor(opCtx.get());
+    auto cursorId1 = pinned1.getCursor()->cursorid();
+    auto cursorId2 = pinned2.getCursor()->cursorid();
+    auto cursorsForNamespace = useCursorManager()->getCursorIdsForNamespace(kTestNss);
+    ASSERT_EQUALS(cursorsForNamespace.size(), 2ull);
+    // The results for cursorsForNamespace won't necessarily be the same as the order of insertion.
+    std::set<CursorId> cursorsForNamespaceSet(cursorsForNamespace.begin(),
+                                              cursorsForNamespace.end());
+
+    ASSERT_EQUALS(cursorsForNamespaceSet.count(cursorId1), 1ull);
+    ASSERT_EQUALS(cursorsForNamespaceSet.count(cursorId2), 1ull);
+}
+
+TEST_F(CursorManagerTestCustomOpCtx,
+       GetCursorIdsForNamespaceDoesNotReturnEntriesForNonMatchingNamespace) {
+    auto opCtx = _queryServiceContext->makeOperationContext();
+    // Add a cursor for kTestNss.
+    auto pinned = makeCursor(opCtx.get());
+    // Get cursors for a different NamespaceString.
+    auto cursorsForNamespace =
+        useCursorManager()->getCursorIdsForNamespace(NamespaceString("somerandom.nss"));
+    ASSERT_EQUALS(cursorsForNamespace.size(), 0ull);
+}
+
 }  // namespace
 }  // namespace mongo