SERVER-93584 Report 'maxTimestampEligibleForTruncate' in pre-image stats (#26972)

GitOrigin-RevId: cbb6b8543feeb6e110f646bbeb44d8779d838db1

5 files changed, 18 insertions, 3 deletions

diff --git a/src/mongo/db/change_stream_pre_images_collection_manager.cpp b/src/mongo/db/change_stream_pre_images_collection_manager.cpp
index 68e735a8570..8db61b3a58d 100644
--- a/src/mongo/db/change_stream_pre_images_collection_manager.cpp
+++ b/src/mongo/db/change_stream_pre_images_collection_manager.cpp
@@ -149,6 +149,7 @@ BSONObj ChangeStreamPreImagesCollectionManager::PurgingJobStats::toBSON() const
         .append("bytesDeleted", bytesDeleted.loadRelaxed())
         .append("scannedCollections", scannedCollections.loadRelaxed())
         .append("scannedInternalCollections", scannedInternalCollections.loadRelaxed())
+        .append("maxTimestampEligibleForTruncate", maxTimestampEligibleForTruncate.loadRelaxed())
         .append("maxStartWallTimeMillis", maxStartWallTime.loadRelaxed().toMillisSinceEpoch())
         .append("timeElapsedMillis", timeElapsedMillis.loadRelaxed());
     return builder.obj();
@@ -468,6 +469,9 @@ size_t ChangeStreamPreImagesCollectionManager::_deleteExpiredPreImagesWithTrunca
     const auto truncateStats =
         _truncateManager.truncateExpiredPreImages(opCtx, std::move(tenantId));
 
+    _purgingJobStats.maxTimestampEligibleForTruncate.store(
+        truncateStats.maxTimestampEligibleForTruncate);
+
     if (truncateStats.maxStartWallTime > _purgingJobStats.maxStartWallTime.loadRelaxed()) {
         _purgingJobStats.maxStartWallTime.store(truncateStats.maxStartWallTime);
     }
@@ -478,7 +482,6 @@ size_t ChangeStreamPreImagesCollectionManager::_deleteExpiredPreImagesWithTrunca
         truncateStats.scannedInternalCollections);
 
     _purgingJobStats.scannedCollections.fetchAndAddRelaxed(1);
-
     return truncateStats.docsDeleted;
 }
 
diff --git a/src/mongo/db/change_stream_pre_images_collection_manager.h b/src/mongo/db/change_stream_pre_images_collection_manager.h
index a5e4935b2dc..57c5a49ef03 100644
--- a/src/mongo/db/change_stream_pre_images_collection_manager.h
+++ b/src/mongo/db/change_stream_pre_images_collection_manager.h
@@ -109,6 +109,12 @@ public:
         AtomicWord<Date_t> maxStartWallTime;
 
         /**
+         * The maximum timestamp expired pre-images, in the most recent pass, could have to be
+         * eligible for truncate.
+         */
+        AtomicWord<Timestamp> maxTimestampEligibleForTruncate;
+
+        /**
          * Serializes the purging job statistics to the BSON object.
          */
         BSONObj toBSON() const;
diff --git a/src/mongo/db/change_stream_pre_images_remover_test.cpp b/src/mongo/db/change_stream_pre_images_remover_test.cpp
index 1c08b20f347..485d8c656c1 100644
--- a/src/mongo/db/change_stream_pre_images_remover_test.cpp
+++ b/src/mongo/db/change_stream_pre_images_remover_test.cpp
@@ -730,6 +730,7 @@ TEST_F(PreImagesRemoverTest, TruncatesAreOnlyAfterAllDurable) {
     setExpirationTime(Seconds{1});
 
     auto passStats = performPass(Milliseconds{0});
+    ASSERT_EQ(passStats["maxTimestampEligibleForTruncate"].timestamp(), allDurableTS);
     ASSERT_EQ(passStats["totalPass"].numberLong(), 1);
     ASSERT_EQ(passStats["docsDeleted"].numberLong(), numRecordsBeforeAllDurableTimestamp);
     ASSERT_EQ(passStats["scannedInternalCollections"].numberLong(), 1);
diff --git a/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.cpp b/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.cpp
index b13aa1f2436..7aa81abf674 100644
--- a/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.cpp
+++ b/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.cpp
@@ -532,12 +532,14 @@ PreImagesTruncateStats PreImagesTenantMarkers::truncateExpiredPreImages(Operatio
         opCtx, NamespaceStringOrUUID{_preImagesCollectionNss.dbName(), _preImagesCollectionUUID});
     const auto& preImagesColl = preImagesCollection.getCollectionPtr();
 
+    PreImagesTruncateStats stats;
+
     // All pre-images with 'ts' <= 'maxTSEligibleForTruncate' are candidates for truncation.
     // However, pre-images with 'ts' > 'maxTSEligibleForTruncate' are unsafe to truncate, as
     // there may be oplog holes or inconsistent data prior to it. Compute the value once, as it
     // requires making an additional call into the storage engine.
     Timestamp maxTSEligibleForTruncate = getMaxTSEligibleForTruncate(opCtx);
-
+    stats.maxTimestampEligibleForTruncate = maxTSEligibleForTruncate;
 
     // TODO SERVER-90305: Explore options for handling rollback-to-stable with truncate markers.
     //
@@ -553,7 +555,6 @@ PreImagesTruncateStats PreImagesTenantMarkers::truncateExpiredPreImages(Operatio
     //      (3) If a truncate is issued on data that is later rolled back, unexpired pre-images will
     //      be rolled back in the process. From the stable timestamp, oplog entries will be replayed
     //      and re-inserted into truncate markers (mirroring truncate behavior in a stable state).
-    PreImagesTruncateStats stats;
     for (auto& [nsUUID, truncateMarkersForNsUUID] : *markersMapSnapshot) {
         RecordId minRecordId =
             change_stream_pre_image_util::getAbsoluteMinPreImageRecordIdBoundForNs(nsUUID)
diff --git a/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.h b/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.h
index 5266bb928f0..4d453a683d6 100644
--- a/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.h
+++ b/src/mongo/db/change_stream_pre_images_tenant_truncate_markers.h
@@ -50,6 +50,10 @@ struct PreImagesTruncateStats {
     // The number of 'nsUUID's scanned in the truncate pass.
     int64_t scannedInternalCollections{0};
 
+    // Instantaneous maximum timestamp eligible for truncation. Expired documents will only be
+    // truncated when their timestamp is less than or equal to it.
+    Timestamp maxTimestampEligibleForTruncate;
+
     // The maximum wall time from the pre-images truncated across the collection.
     Date_t maxStartWallTime{};
 };