SERVER-28120 persist config.collections entries on shards for the collections that the shards possess

1 files changed, 114 insertions, 0 deletions

diff --git a/src/mongo/db/s/shard_metadata_util.h b/src/mongo/db/s/shard_metadata_util.h
new file mode 100644
index 00000000000..2acbd138a1c
--- /dev/null
+++ b/src/mongo/db/s/shard_metadata_util.h
@@ -0,0 +1,114 @@
+/**
+ *    Copyright (C) 2017 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "mongo/base/status.h"
+
+namespace mongo {
+
+class BSONObj;
+class ChunkType;
+class CollectionMetadata;
+class ShardCollectionType;
+class NamespaceString;
+class OID;
+class OperationContext;
+class ShardingCatalogClient;
+template <typename T>
+class StatusWith;
+
+/**
+ * Function helpers to locally, using a DBDirectClient, read and write sharding metadata on a shard.
+ * Also retrieves metadata from the config server, copies of which are then persisted on the shard.
+ */
+namespace shardmetadatautil {
+
+/**
+ * Gets the config.collections for 'nss' entry either remotely from the config server if
+ * 'isShardPrimary' is true or locally from the shard if false. Additionally updates the shard's
+ * config.collections entry with the remotely retrieved metadata if 'isShardPrimary' is true.
+ */
+StatusWith<std::pair<BSONObj, OID>> getCollectionShardKeyAndEpoch(
+    OperationContext* opCtx,
+    ShardingCatalogClient* catalogClient,
+    const NamespaceString& nss,
+    bool isShardPrimary);
+
+/**
+ * Reads the shard server's config.collections entry identified by 'nss'.
+ */
+StatusWith<ShardCollectionType> readShardCollectionEntry(OperationContext* opCtx,
+                                                         const NamespaceString& nss);
+
+/**
+ * Updates the config.collections entry matching 'query' with 'update' using local write concern.
+ * Only the fields specified in 'update' are modified.
+ * Sets upsert to true on the update operation in case the entry does not exist locally yet.
+ */
+Status updateCollectionEntry(OperationContext* opCtx,
+                             const NamespaceString& nss,
+                             const BSONObj& query,
+                             const BSONObj& update);
+
+/**
+ * Two threads running this function in parallel for the same collection can corrupt the collection
+ * data!
+ *
+ * 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 and a RemoteChangeDetected error returned.
+ *
+ * @nss - the regular collection namespace for which chunk metadata is being updated.
+ * @chunks - chunks retrieved from the config server, sorted in ascending chunk version order
+ * @currEpoch - what this shard server expects to be the collection epoch.
+ *
+ * Returns:
+ * - RemoteChangeDetected if the chunk version epoch of any chunk in 'chunks' is different than
+ * 'currEpoch'
+ * - Other errors if unable to do local writes/reads to the config.chunks.ns colection.
+ */
+Status writeNewChunks(OperationContext* opCtx,
+                      const NamespaceString& nss,
+                      const std::vector<ChunkType>& chunks,
+                      const OID& currEpoch);
+
+/**
+ * Locally on this shard, drops the config.chunks.ns corresponding to 'chunkMetadataNss' and then
+ * deletes the config.collections entry for 'collectionEntryNss'.
+ */
+Status dropChunksAndDeleteCollectionsEntry(OperationContext* opCtx,
+                                           const NamespaceString& chunkMetadataNss,
+                                           const NamespaceString& collectionsEntryNss);
+
+}  // namespace shardmetadatautil
+}  // namespace mongo