SERVER-65208 Check the top-chunk before refreshing the local metadata

1 files changed, 44 insertions, 40 deletions

diff --git a/src/mongo/db/s/split_chunk.cpp b/src/mongo/db/s/split_chunk.cpp
index cd3f7d15322..a97efd9be55 100644
--- a/src/mongo/db/s/split_chunk.cpp
+++ b/src/mongo/db/s/split_chunk.cpp
@@ -163,6 +163,49 @@ StatusWith<boost::optional<ChunkRange>> splitChunk(OperationContext* opCtx,
                                      std::move(splitPoints),
                                      fromChunkSplitter);
 
+    // Get the chunk containing a single document (if any) to perform the top-chunk optimization.
+    auto topChunkRange = [&] {
+        AutoGetCollection collection(opCtx, nss, MODE_IS);
+        if (!collection) {
+            LOGV2_WARNING(23778,
+                          "will not perform top-chunk checking since {namespace} does not "
+                          "exist after splitting",
+                          logAttrs(nss));
+            return boost::optional<ChunkRange>(boost::none);
+        }
+
+        // Allow multiKey based on the invariant that shard keys must be single-valued.
+        // Therefore, any multi-key index prefixed by shard key cannot be multikey over the
+        // shard key fields.
+        auto shardKeyIdx = findShardKeyPrefixedIndex(opCtx,
+                                                     *collection,
+                                                     collection->getIndexCatalog(),
+                                                     keyPatternObj,
+                                                     false /* requireSingleKey */);
+        if (!shardKeyIdx) {
+            return boost::optional<ChunkRange>(boost::none);
+        }
+
+        auto backChunk = ChunkType();
+        backChunk.setMin(request.getSplitPoints().back());
+        backChunk.setMax(chunkRange.getMax());
+
+        auto frontChunk = ChunkType();
+        frontChunk.setMin(chunkRange.getMin());
+        frontChunk.setMax(request.getSplitPoints().front());
+
+        KeyPattern shardKeyPattern(keyPatternObj);
+        if (shardKeyPattern.globalMax().woCompare(backChunk.getMax()) == 0 &&
+            checkIfSingleDoc(opCtx, collection.getCollection(), *shardKeyIdx, &backChunk)) {
+            return boost::optional<ChunkRange>(ChunkRange(backChunk.getMin(), backChunk.getMax()));
+        } else if (shardKeyPattern.globalMin().woCompare(frontChunk.getMin()) == 0 &&
+                   checkIfSingleDoc(opCtx, collection.getCollection(), *shardKeyIdx, &frontChunk)) {
+            return boost::optional<ChunkRange>(
+                ChunkRange(frontChunk.getMin(), frontChunk.getMax()));
+        }
+        return boost::optional<ChunkRange>(boost::none);
+    }();
+
     auto configCmdObj =
         request.toConfigCommandBSON(ShardingCatalogClient::kMajorityWriteConcern.toBSON());
 
@@ -202,14 +245,11 @@ StatusWith<boost::optional<ChunkRange>> splitChunk(OperationContext* opCtx,
         return commandStatus;
     }
 
-    //
     // If _configsvrCommitChunkSplit returned an error, look at the metadata to
     // determine if the split actually did happen. This can happen if there's a network error
     // getting the response from the first call to _configsvrCommitChunkSplit, but it actually
     // succeeds, thus the automatic retry fails with a precondition violation, for example.
-    //
     if (!commandStatus.isOK() || !writeConcernStatus.isOK()) {
-
         if (checkMetadataForSuccessfulSplitChunk(
                 opCtx, nss, expectedCollectionEpoch, chunkRange, request.getSplitPoints())) {
             // Split was committed.
@@ -220,43 +260,7 @@ StatusWith<boost::optional<ChunkRange>> splitChunk(OperationContext* opCtx,
         }
     }
 
-    AutoGetCollection collection(opCtx, nss, MODE_IS);
-    if (!collection) {
-        LOGV2_WARNING(
-            23778,
-            "will not perform top-chunk checking since {namespace} does not exist after splitting",
-            logAttrs(nss));
-        return boost::optional<ChunkRange>(boost::none);
-    }
-
-    // Allow multiKey based on the invariant that shard keys must be single-valued. Therefore,
-    // any multi-key index prefixed by shard key cannot be multikey over the shard key fields.
-    auto shardKeyIdx = findShardKeyPrefixedIndex(opCtx,
-                                                 *collection,
-                                                 collection->getIndexCatalog(),
-                                                 keyPatternObj,
-                                                 /*requireSingleKey=*/false);
-    if (!shardKeyIdx) {
-        return boost::optional<ChunkRange>(boost::none);
-    }
-
-    auto backChunk = ChunkType();
-    backChunk.setMin(request.getSplitPoints().back());
-    backChunk.setMax(chunkRange.getMax());
-
-    auto frontChunk = ChunkType();
-    frontChunk.setMin(chunkRange.getMin());
-    frontChunk.setMax(request.getSplitPoints().front());
-
-    KeyPattern shardKeyPattern(keyPatternObj);
-    if (shardKeyPattern.globalMax().woCompare(backChunk.getMax()) == 0 &&
-        checkIfSingleDoc(opCtx, collection.getCollection(), *shardKeyIdx, &backChunk)) {
-        return boost::optional<ChunkRange>(ChunkRange(backChunk.getMin(), backChunk.getMax()));
-    } else if (shardKeyPattern.globalMin().woCompare(frontChunk.getMin()) == 0 &&
-               checkIfSingleDoc(opCtx, collection.getCollection(), *shardKeyIdx, &frontChunk)) {
-        return boost::optional<ChunkRange>(ChunkRange(frontChunk.getMin(), frontChunk.getMax()));
-    }
-    return boost::optional<ChunkRange>(boost::none);
+    return topChunkRange;
 }
 
 }  // namespace mongo