SERVER-80188 Remove epoch from migration source manager once 8.0 becomes last-lts (#35323)

pierlauro · MongoDB Bot · commit 1ac9c53eadb5 · 2025-04-28T09:23:01.000Z
GitOrigin-RevId: fd4fdd60c6c52b2122cf8b82813225a96d9811f7
diff --git a/src/mongo/db/s/active_migrations_registry_test.cpp b/src/mongo/db/s/active_migrations_registry_test.cpp
@@ -67,8 +67,7 @@ ShardsvrMoveRange createMoveRangeRequest(const NamespaceString& nss,
                                          const OID& epoch = OID::gen()) {
     const ShardId fromShard = ShardId("shard0001");
     const long long maxChunkSizeBytes = 1024;
-    ShardsvrMoveRange req(nss, fromShard, maxChunkSizeBytes);
-    req.setEpoch(epoch);
+    ShardsvrMoveRange req(nss, Timestamp(10), fromShard, maxChunkSizeBytes);
     req.getMoveRangeRequestBase().setToShard(ShardId("shard0002"));
     req.setMaxChunkSizeBytes(1024);
     req.getMoveRangeRequestBase().setMin(BSON("Key" << -100));
diff --git a/src/mongo/db/s/balancer/balancer.cpp b/src/mongo/db/s/balancer/balancer.cpp
@@ -415,7 +415,6 @@ void enqueueChunkMigrations(OperationContext* opCtx,
         shardSvrRequest.setMaxChunkSizeBytes(maxChunkSizeBytes);
         shardSvrRequest.setFromShard(migrateInfo.from);
         shardSvrRequest.setCollectionTimestamp(migrateInfo.version.getTimestamp());
-        shardSvrRequest.setEpoch(migrateInfo.version.epoch());
         shardSvrRequest.setForceJumbo(migrateInfo.forceJumbo);
         const auto [secondaryThrottle, wc] =
             getSecondaryThrottleAndWriteConcern(balancerConfig->getSecondaryThrottle());
@@ -778,7 +777,6 @@ Status Balancer::moveRange(OperationContext* opCtx,
     shardSvrRequest.setMaxChunkSizeBytes(maxChunkSize);
     shardSvrRequest.setFromShard(fromShardId);
     shardSvrRequest.setCollectionTimestamp(coll.getTimestamp());
-    shardSvrRequest.setEpoch(coll.getEpoch());
     const auto [secondaryThrottle, wc] =
         getSecondaryThrottleAndWriteConcern(request.getSecondaryThrottle());
     shardSvrRequest.setSecondaryThrottle(secondaryThrottle);
diff --git a/src/mongo/db/s/balancer/balancer_commands_scheduler_test.cpp b/src/mongo/db/s/balancer/balancer_commands_scheduler_test.cpp
@@ -111,7 +111,7 @@ class BalancerCommandsSchedulerTest : public ConfigServerTestFixture {
         shardSvrRequest.setDbName(DatabaseName::kAdmin);
         shardSvrRequest.setMoveRangeRequestBase(base);
         shardSvrRequest.setFromShard(from);
-        shardSvrRequest.setEpoch(OID::gen());
+        shardSvrRequest.setCollectionTimestamp(Timestamp(10));
         shardSvrRequest.setMaxChunkSizeBytes(1024 * 1024);
 
         return shardSvrRequest;
diff --git a/src/mongo/db/s/migration_chunk_cloner_source_test.cpp b/src/mongo/db/s/migration_chunk_cloner_source_test.cpp
@@ -759,7 +759,7 @@ class MigrationChunkClonerSourceTest : public ShardServerTestFixture {
      */
     static ShardsvrMoveRange createMoveRangeRequest(const ChunkRange& chunkRange) {
         ShardsvrMoveRange req(kNss);
-        req.setEpoch(OID::gen());
+        req.setCollectionTimestamp(Timestamp(10));
         req.setFromShard(ShardId(kDonorConnStr.getSetName()));
         req.setMaxChunkSizeBytes(1024);
         req.getMoveRangeRequestBase().setToShard(ShardId(kRecipientConnStr.getSetName()));
diff --git a/src/mongo/db/s/migration_source_manager.cpp b/src/mongo/db/s/migration_source_manager.cpp
@@ -199,8 +199,12 @@ MigrationSourceManager MigrationSourceManager::createMigrationSourceManager(
             AutoGetCollection autoColl(opCtx, nss, MODE_IS);
             const auto scopedCsr =
                 CollectionShardingRuntime::assertCollectionLockedAndAcquireShared(opCtx, nss);
-            const auto [metadata, _] = checkCollectionIdentity(
-                opCtx, nss, args.getEpoch(), args.getCollectionTimestamp(), *autoColl, *scopedCsr);
+            const auto [metadata, _] = checkCollectionIdentity(opCtx,
+                                                               nss,
+                                                               boost::none /* epoch */,
+                                                               args.getCollectionTimestamp(),
+                                                               *autoColl,
+                                                               *scopedCsr);
             return metadata;
         }();
 
@@ -259,7 +263,8 @@ MigrationSourceManager::MigrationSourceManager(OperationContext* opCtx,
                         _args.getMax(),
                         6,  // Total number of steps
                         _args.getToShard(),
-                        _args.getFromShard()) {
+                        _args.getFromShard()),
+      _collectionTimestamp(_args.getCollectionTimestamp()) {
     // Since the MigrationSourceManager is registered on the CSR from the constructor, another
     // thread can get it and abort the migration (and get a reference to the completion promise's
     // future). When this happens, since we throw an exception from the constructor, the destructor
@@ -279,8 +284,12 @@ MigrationSourceManager::MigrationSourceManager(OperationContext* opCtx,
         auto scopedCsr =
             CollectionShardingRuntime::assertCollectionLockedAndAcquireExclusive(opCtx, nss());
 
-        auto [metadata, indexInfo] = checkCollectionIdentity(
-            _opCtx, nss(), _args.getEpoch(), _args.getCollectionTimestamp(), *autoColl, *scopedCsr);
+        auto [metadata, indexInfo] = checkCollectionIdentity(_opCtx,
+                                                             nss(),
+                                                             boost::none /* epoch */,
+                                                             _args.getCollectionTimestamp(),
+                                                             *autoColl,
+                                                             *scopedCsr);
 
         UUID collectionUUID = autoColl.getCollection()->uuid();
 
@@ -350,9 +359,7 @@ MigrationSourceManager::MigrationSourceManager(OperationContext* opCtx,
                           collectionIndexInfo,
                           ChunkRange(*_args.getMin(), *_args.getMax()));
 
-    _collectionEpoch = _args.getEpoch();
     _collectionUUID = collectionUUID;
-    _collectionTimestamp = _args.getCollectionTimestamp();
 
     _chunkVersion = collectionMetadata.getChunkManager()
                         ->findIntersectingChunkWithSimpleCollation(*_args.getMin())
@@ -776,27 +783,16 @@ CollectionMetadata MigrationSourceManager::_getCurrentMetadataAndCheckForConflic
                 optMetadata);
         return *optMetadata;
     }();
-    if (_collectionTimestamp) {
-        uassert(ErrorCodes::ConflictingOperationInProgress,
-                str::stream()
-                    << "The collection's timestamp has changed since the migration began. Expected "
-                       "timestamp: "
-                    << _collectionTimestamp->toStringPretty() << ", but found: "
-                    << (metadata.isSharded()
-                            ? metadata.getCollPlacementVersion().getTimestamp().toStringPretty()
-                            : "unsharded collection"),
-                metadata.isSharded() &&
-                    *_collectionTimestamp == metadata.getCollPlacementVersion().getTimestamp());
-    } else {
-        uassert(
-            ErrorCodes::ConflictingOperationInProgress,
+    uassert(ErrorCodes::ConflictingOperationInProgress,
             str::stream()
-                << "The collection's epoch has changed since the migration began. Expected epoch: "
-                << _collectionEpoch->toString() << ", but found: "
-                << (metadata.isSharded() ? metadata.getCollPlacementVersion().toString()
-                                         : "unsharded collection"),
-            metadata.isSharded() && metadata.getCollPlacementVersion().epoch() == _collectionEpoch);
-    }
+                << "The collection's timestamp has changed since the migration began. Expected "
+                   "timestamp: "
+                << _collectionTimestamp.toStringPretty() << ", but found: "
+                << (metadata.isSharded()
+                        ? metadata.getCollPlacementVersion().getTimestamp().toStringPretty()
+                        : "unsharded collection"),
+            metadata.isSharded() &&
+                _collectionTimestamp == metadata.getCollPlacementVersion().getTimestamp());
 
     return metadata;
 }
diff --git a/src/mongo/db/s/migration_source_manager.h b/src/mongo/db/s/migration_source_manager.h
@@ -288,13 +288,11 @@ class MigrationSourceManager {
     };
     boost::optional<ScopedRegisterer> _scopedRegisterer;
 
-    // The epoch of the collection being migrated and its UUID, as of the time the migration
-    // started. Values are boost::optional only up until the constructor runs, because UUID doesn't
-    // have a default constructor.
-    // TODO SERVER-80188: remove _collectionEpoch once 8.0 becomes last-lts.
-    boost::optional<OID> _collectionEpoch;
+    // The UUID and timesetamp of the collection being migrated. The UUID values is boost::optional
+    // only up until the constructor runs, because UUID doesn't have a default constructor.
     boost::optional<UUID> _collectionUUID;
-    boost::optional<Timestamp> _collectionTimestamp;
+
+    Timestamp _collectionTimestamp;
 
     // The version of the chunk at the time the migration started.
     boost::optional<ChunkVersion> _chunkVersion;
diff --git a/src/mongo/s/request_types/move_range_request.idl b/src/mongo/s/request_types/move_range_request.idl
@@ -130,15 +130,9 @@ commands:
         chained_structs:
             MoveRangeRequestBase: MoveRangeRequestBase
         fields:
-            # TODO SERVER-80188: remove _collectionEpoch once 8.0 becomes last-lts.
-            epoch:
-                type: objectid
-                description: "Epoch of the collection"
-                optional: true
             collectionTimestamp:
                 type: timestamp
                 description: "Timestamp of the collection"
-                optional: true
             fromShard:
                 type: shard_id
                 description: "ID of the donor shard"
