SERVER-20854 Pull the diff tracker's query generation logic outside of the template

4 files changed, 18 insertions, 29 deletions

diff --git a/src/mongo/db/s/metadata_loader.cpp b/src/mongo/db/s/metadata_loader.cpp
index 762b1382412..2a57f654d84 100644
--- a/src/mongo/db/s/metadata_loader.cpp
+++ b/src/mongo/db/s/metadata_loader.cpp
@@ -183,9 +183,9 @@ Status MetadataLoader::_initChunks(OperationContext* txn,
         ns, &metadata->_chunksMap, &metadata->_collVersion, &versionMap, shard);
 
     try {
-        // Get any new chunks.
+        const auto diffQuery = SCMConfigDiffTracker::createConfigDiffQuery(NamespaceString(ns),
+                                                                           metadata->_collVersion);
         std::vector<ChunkType> chunks;
-        const auto diffQuery = differ.configDiffQuery();
         Status status = catalogClient->getChunks(txn,
                                                  diffQuery.query,
                                                  diffQuery.sort,
diff --git a/src/mongo/s/chunk_diff.cpp b/src/mongo/s/chunk_diff.cpp
index 6e065a44e9a..90ec41b8923 100644
--- a/src/mongo/s/chunk_diff.cpp
+++ b/src/mongo/s/chunk_diff.cpp
@@ -32,6 +32,7 @@
 
 #include "mongo/s/chunk_diff.h"
 
+#include "mongo/db/namespace_string.h"
 #include "mongo/db/s/collection_metadata.h"
 #include "mongo/s/catalog/type_chunk.h"
 #include "mongo/s/chunk_version.h"
@@ -169,36 +170,26 @@ int ConfigDiffTracker<ValType>::calculateConfigDiff(OperationContext* txn,
     return _validDiffs;
 }
 
-template <class ValType>
-typename ConfigDiffTracker<ValType>::QueryAndSort ConfigDiffTracker<ValType>::configDiffQuery()
-    const {
+ConfigDiffTrackerBase::QueryAndSort ConfigDiffTrackerBase::createConfigDiffQuery(
+    const NamespaceString& nss, ChunkVersion collectionVersion) {
     // The query has to find all the chunks $gte the current max version. Currently, any splits and
     // merges will increment the current max version.
     BSONObjBuilder queryB;
-    queryB.append(ChunkType::ns(), _ns);
+    queryB.append(ChunkType::ns(), nss.ns());
 
     {
         BSONObjBuilder tsBuilder(queryB.subobjStart(ChunkType::DEPRECATED_lastmod()));
-        tsBuilder.appendTimestamp("$gte", _maxVersion->toLong());
+        tsBuilder.appendTimestamp("$gte", collectionVersion.toLong());
         tsBuilder.done();
     }
 
     // NOTE: IT IS IMPORTANT FOR CONSISTENCY THAT WE SORT BY ASC VERSION, IN ORDER TO HANDLE CURSOR
-    // YIELDING BETWEEN CHUNKS BEING MIGRATED.
+    // YIELDING BETWEEN CHUNKS BEING MIGRATED
     //
     // This ensures that changes to chunk version (which will always be higher) will always come
     // *after* our current position in the chunk cursor.
 
-    QueryAndSort queryObj(queryB.obj(), BSON(ChunkType::DEPRECATED_lastmod() << 1));
-
-    LOG(2) << "major version query from " << *_maxVersion << " and over "
-           << _maxShardVersions->size() << " shards is " << queryObj;
-
-    return queryObj;
-}
-
-std::string ConfigDiffTrackerBase::QueryAndSort::toString() const {
-    return str::stream() << "query: " << query << ", sort: " << sort;
+    return QueryAndSort{queryB.obj(), BSON(ChunkType::DEPRECATED_lastmod() << 1)};
 }
 
 // Ensures that these instances of the template are compiled
diff --git a/src/mongo/s/chunk_diff.h b/src/mongo/s/chunk_diff.h
index cf691358f38..9ea6ed5b62e 100644
--- a/src/mongo/s/chunk_diff.h
+++ b/src/mongo/s/chunk_diff.h
@@ -46,13 +46,15 @@ public:
      * Structure repsenting the generated query and sort order for a chunk diffing operation.
      */
     struct QueryAndSort {
-        QueryAndSort(BSONObj inQuery, BSONObj inSort) : query(inQuery), sort(inSort) {}
-
-        std::string toString() const;
-
         const BSONObj query;
         const BSONObj sort;
     };
+
+    /**
+     * Returns the query needed to find incremental changes to a collection from the config server.
+     */
+    static QueryAndSort createConfigDiffQuery(const NamespaceString& nss,
+                                              ChunkVersion collectionVersion);
 };
 
 /**
@@ -103,10 +105,6 @@ public:
     // Returns the number of diffs processed, or -1 if the diffs were inconsistent.
     int calculateConfigDiff(OperationContext* txn, const std::vector<ChunkType>& chunks);
 
-    // Returns the query needed to find new changes to a collection from the config server
-    // Needed only if a custom connection is required to the config server
-    QueryAndSort configDiffQuery() const;
-
 protected:
     /**
      * Determines which chunks are actually being remembered by our RangeMap. Allows individual
diff --git a/src/mongo/s/chunk_manager.cpp b/src/mongo/s/chunk_manager.cpp
index be9ee5a25eb..75f2cc7c11c 100644
--- a/src/mongo/s/chunk_manager.cpp
+++ b/src/mongo/s/chunk_manager.cpp
@@ -243,13 +243,13 @@ bool ChunkManager::_load(OperationContext* txn,
                << oldChunkMap.size() << " chunks";
     }
 
+    // Get the diff query required
+    const auto diffQuery = CMConfigDiffTracker::createConfigDiffQuery(_nss, _version);
+
     // Attach a diff tracker for the versioned chunk data
     CMConfigDiffTracker differ(_nss.ns(), &chunkMap, &_version, shardVersions, this);
 
     // Diff tracker should *always* find at least one chunk if collection exists
-    // Get the diff query required
-    auto diffQuery = differ.configDiffQuery();
-
     repl::OpTime opTime;
     std::vector<ChunkType> chunks;
     uassertStatusOK(Grid::get(txn)->catalogClient(txn)->getChunks(