SERVER-56515 Make mergeChunks consider the 'incrementChunkMajorVersionOnChunkSplits' parameter

(cherry picked from commit 9261befabc2f3e922eec0f15e091e9881deb1960)

2 files changed, 49 insertions, 10 deletions

diff --git a/jstests/sharding/major_version_check.js b/jstests/sharding/major_version_check.js
index 0a55fdc8702..549b92ea47f 100644
--- a/jstests/sharding/major_version_check.js
+++ b/jstests/sharding/major_version_check.js
@@ -4,8 +4,7 @@
 (function() {
 'use strict';
 
-// Test with default value of incrementChunkMajorVersionOnChunkSplits, which is
-// false>
+// Test with default value of incrementChunkMajorVersionOnChunkSplits, which is false
 (() => {
     var st = new ShardingTest({shards: 1, mongos: 2});
 
@@ -51,6 +50,11 @@
     assert.eq(Timestamp(1, 0),
               staleMongos.getDB("admin").runCommand({getShardVersion: coll + ""}).version);
 
+    // Merge the just-split chunks and ensure the major version didn't go up
+    assert.commandWorked(
+        admin.runCommand({mergeChunks: coll + "", bounds: [{_id: MinKey}, {_id: MaxKey}]}));
+    assert.eq(Timestamp(1, 3), admin.runCommand({getShardVersion: coll + ""}).version);
+
     st.stop();
 })();
 
@@ -124,6 +128,11 @@
     assert.eq(Timestamp(2, 2),
               staleMongos.getDB("admin").runCommand({getShardVersion: coll + ""}).version);
 
+    // Merge the just-split chunks and ensure the major version went up
+    assert.commandWorked(
+        admin.runCommand({mergeChunks: coll + "", bounds: [{_id: MinKey}, {_id: MaxKey}]}));
+    assert.eq(Timestamp(3, 0), admin.runCommand({getShardVersion: coll + ""}).version);
+
     st.stop();
 })();
 })();
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp b/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
index 83d3eafb10f..f07c54d6341 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_chunk_operations.cpp
@@ -357,12 +357,12 @@ Status ShardingCatalogManager::commitChunkSplit(OperationContext* opCtx,
 
     ChunkVersion currentMaxVersion = collVersion;
 
-    // If the incrementChunkMajorVersionOnChunkSplits flag is set, increment
-    // the major version only if the shard that owns the chunk being split has
-    // version == collection version. See SERVER-41480 for details.
+    // If the incrementChunkMajorVersionOnChunkSplits flag is set, increment the major version only
+    // if the shard that owns the chunk being split has shardVersion == collectionVersion. See
+    // SERVER-41480 for details.
     //
-    // This flag is only useful if there are some 4.0 routers still in the
-    // cluster, so we only use it if FCV is not fully upgraded.
+    // This flag is only useful if there are some 4.0 routers still in the cluster, so we only use
+    // it if FCV is not fully upgraded.
     const auto currentFCV = serverGlobalParams.featureCompatibility.getVersion();
     if (currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42 &&
         incrementChunkMajorVersionOnChunkSplits.load() && shardVersion == collVersion) {
@@ -558,8 +558,7 @@ Status ShardingCatalogManager::commitChunkMerge(OperationContext* opCtx,
             1));                             // Limit 1.
 
     if (!swCollVersion.isOK()) {
-        return swCollVersion.getStatus().withContext(str::stream()
-                                                     << "mergeChunk cannot merge chunks.");
+        return swCollVersion.getStatus().withContext("mergeChunk cannot merge chunks.");
     }
 
     auto collVersion = swCollVersion.getValue();
@@ -571,6 +570,25 @@ Status ShardingCatalogManager::commitChunkMerge(OperationContext* opCtx,
                 "that the collection was dropped and re-created."};
     }
 
+    // Get the shard version (max chunk version) for the shard requesting the merge.
+    auto swShardVersion = getMaxChunkVersionFromQueryResponse(
+        nss,
+        Grid::get(opCtx)->shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
+            opCtx,
+            ReadPreferenceSetting{ReadPreference::PrimaryOnly},
+            repl::ReadConcernLevel::kLocalReadConcern,
+            ChunkType::ConfigNS,
+            BSON("ns" << nss.ns() << "shard"
+                      << shardName),         // Query all chunks for this namespace and shard.
+            BSON(ChunkType::lastmod << -1),  // Sort by version.
+            1));                             // Limit 1.
+
+    if (!swShardVersion.isOK()) {
+        return swShardVersion.getStatus().withContext("mergeChunk cannot merge chunks.");
+    }
+
+    auto shardVersion = swShardVersion.getValue();
+
     // Build chunks to be merged
     std::vector<ChunkType> chunksToMerge;
 
@@ -608,7 +626,19 @@ Status ShardingCatalogManager::commitChunkMerge(OperationContext* opCtx,
     }
 
     ChunkVersion mergeVersion = collVersion;
-    mergeVersion.incMinor();
+    // If the incrementChunkMajorVersionOnChunkSplits flag is set, increment the major version only
+    // if the shard that owns the chunks being merged has shardVersion == collectionVersion. See
+    // SERVER-41480 for details.
+    //
+    // This flag is only useful if there are some 4.0 routers still in the cluster, so we only use
+    // it if FCV is not fully upgraded.
+    const auto currentFCV = serverGlobalParams.featureCompatibility.getVersion();
+    if (currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42 &&
+        incrementChunkMajorVersionOnChunkSplits.load() && shardVersion == collVersion) {
+        mergeVersion.incMajor();
+    } else {
+        mergeVersion.incMinor();
+    }
 
     auto updates = buildMergeChunksTransactionUpdates(chunksToMerge, mergeVersion, validAfter);
     auto preCond = buildMergeChunksTransactionPrecond(chunksToMerge, collVersion);