SERVER-27704 persist chunk metadata on shard primary

1 files changed, 27 insertions, 0 deletions

diff --git a/src/mongo/db/s/metadata_loader.h b/src/mongo/db/s/metadata_loader.h
index e4624a73f8f..8c12233da2e 100644
--- a/src/mongo/db/s/metadata_loader.h
+++ b/src/mongo/db/s/metadata_loader.h
@@ -29,14 +29,18 @@
 #pragma once
 
 #include <string>
+#include <vector>
 
 #include "mongo/base/status.h"
 
 namespace mongo {
 
 class ShardingCatalogClient;
+class ChunkType;
 class CollectionMetadata;
 class CollectionType;
+class NamespaceString;
+class OID;
 class OperationContext;
 
 /**
@@ -125,6 +129,29 @@ private:
                               const std::string& shard,
                               const CollectionMetadata* oldMetadata,
                               CollectionMetadata* metadata);
+
+
+    /**
+     * Takes a vector of 'chunks' and updates the config.chunks.ns collection specified by 'nss'.
+     * Any chunk documents in config.chunks.ns that overlap with a chunk in 'chunks' is removed
+     * as the new chunk document is inserted. If the epoch of any chunk in 'chunks' does not match
+     * 'currEpoch', the chunk metadata is dropped.
+     *
+     * @nss - the regular collection namespace for which chunk metadata is being updated.
+     * @chunks - a range of chunks retrieved from the config server, sorted in ascending chunk
+     * version order.
+     * @currEpoch - what this shard server knows to be the collection epoch.
+     *
+     * Returns:
+     * - OK if not primary and no writes are needed.
+     * - RemoteChangeDetected if the chunk version epoch of any chunk in 'chunks' is different than
+     * 'currEpoch'
+     * - Other errors in writes/reads to the config.chunks.ns collection fails.
+     */
+    static Status _writeNewChunksIfPrimary(OperationContext* txn,
+                                           const NamespaceString& nss,
+                                           const std::vector<ChunkType>& chunks,
+                                           const OID& currEpoch);
 };
 
 }  // namespace mongo