SERVER-43617 Add metrics on the mongos to indicate the number of shards targeted for CRUD and agg commands

7 files changed, 41 insertions, 0 deletions

diff --git a/src/mongo/s/write_ops/batch_write_exec.cpp b/src/mongo/s/write_ops/batch_write_exec.cpp
index 0fd8842ce92..0020eb137f8 100644
--- a/src/mongo/s/write_ops/batch_write_exec.cpp
+++ b/src/mongo/s/write_ops/batch_write_exec.cpp
@@ -455,6 +455,10 @@ void BatchWriteExec::executeBatch(OperationContext* opCtx,
         }
     }
 
+    auto nShardsOwningChunks = batchOp.getNShardsOwningChunks();
+    if (nShardsOwningChunks.is_initialized())
+        stats->noteNumShardsOwningChunks(nShardsOwningChunks.get());
+
     batchOp.buildClientResponse(clientResponse);
 
     LOG(4) << "Finished execution of write batch"
@@ -476,6 +480,10 @@ void BatchWriteExecStats::noteWriteAt(const HostAndPort& host,
     _writeOpTimes[ConnectionString(host)] = HostOpTime(opTime, electionId);
 }
 
+void BatchWriteExecStats::noteNumShardsOwningChunks(const int nShardsOwningChunks) {
+    _numShardsOwningChunks.emplace(nShardsOwningChunks);
+}
+
 const std::set<ShardId>& BatchWriteExecStats::getTargetedShards() const {
     return _targetedShards;
 }
@@ -484,4 +492,8 @@ const HostOpTimeMap& BatchWriteExecStats::getWriteOpTimes() const {
     return _writeOpTimes;
 }
 
+const boost::optional<int> BatchWriteExecStats::getNumShardsOwningChunks() const {
+    return _numShardsOwningChunks;
+}
+
 }  // namespace mongo
diff --git a/src/mongo/s/write_ops/batch_write_exec.h b/src/mongo/s/write_ops/batch_write_exec.h
index c729561630a..9b6773ecb47 100644
--- a/src/mongo/s/write_ops/batch_write_exec.h
+++ b/src/mongo/s/write_ops/batch_write_exec.h
@@ -94,9 +94,11 @@ public:
 
     void noteWriteAt(const HostAndPort& host, repl::OpTime opTime, const OID& electionId);
     void noteTargetedShard(const ShardId& shardId);
+    void noteNumShardsOwningChunks(const int nShardsOwningChunks);
 
     const std::set<ShardId>& getTargetedShards() const;
     const HostOpTimeMap& getWriteOpTimes() const;
+    const boost::optional<int> getNumShardsOwningChunks() const;
 
     // Expose via helpers if this gets more complex
 
@@ -114,6 +116,7 @@ public:
 private:
     std::set<ShardId> _targetedShards;
     HostOpTimeMap _writeOpTimes;
+    boost::optional<int> _numShardsOwningChunks;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/s/write_ops/batch_write_op.cpp b/src/mongo/s/write_ops/batch_write_op.cpp
index 309d3f4f83e..47ece031758 100644
--- a/src/mongo/s/write_ops/batch_write_op.cpp
+++ b/src/mongo/s/write_ops/batch_write_op.cpp
@@ -38,6 +38,7 @@
 #include "mongo/db/operation_context.h"
 #include "mongo/db/ops/write_ops_parsers.h"
 #include "mongo/db/s/database_sharding_state.h"
+#include "mongo/s/client/num_hosts_targeted_metrics.h"
 #include "mongo/s/cluster_commands_helpers.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/transaction_router.h"
@@ -435,6 +436,8 @@ Status BatchWriteOp::targetBatch(const NSTargeter& targeter,
         targetedBatches->emplace(batch->getEndpoint().shardName, batch);
     }
 
+    _nShardsOwningChunks = targeter.getNShardsOwningChunks();
+
     return Status::OK();
 }
 
@@ -827,6 +830,10 @@ int BatchWriteOp::numWriteOpsIn(WriteOpState opState) const {
         });
 }
 
+boost::optional<int> BatchWriteOp::getNShardsOwningChunks() {
+    return _nShardsOwningChunks;
+}
+
 void BatchWriteOp::_incBatchStats(const BatchedCommandResponse& response) {
     const auto batchType = _clientRequest.getBatchType();
 
diff --git a/src/mongo/s/write_ops/batch_write_op.h b/src/mongo/s/write_ops/batch_write_op.h
index f4ef76bb2c8..eeccb02d2a0 100644
--- a/src/mongo/s/write_ops/batch_write_op.h
+++ b/src/mongo/s/write_ops/batch_write_op.h
@@ -201,6 +201,8 @@ public:
      */
     int numWriteOpsIn(WriteOpState state) const;
 
+    boost::optional<int> getNShardsOwningChunks();
+
 private:
     /**
      * Maintains the batch execution statistics when a response is received.
@@ -242,6 +244,8 @@ private:
 
     // Set to true if this write is part of a transaction.
     const bool _inTransaction{false};
+
+    boost::optional<int> _nShardsOwningChunks;
 };
 
 /**
diff --git a/src/mongo/s/write_ops/chunk_manager_targeter.cpp b/src/mongo/s/write_ops/chunk_manager_targeter.cpp
index 0d8cce10233..a36fb2b4feb 100644
--- a/src/mongo/s/write_ops/chunk_manager_targeter.cpp
+++ b/src/mongo/s/write_ops/chunk_manager_targeter.cpp
@@ -846,6 +846,14 @@ Status ChunkManagerTargeter::refreshIfNeeded(OperationContext* opCtx, bool* wasC
     MONGO_UNREACHABLE;
 }
 
+int ChunkManagerTargeter::getNShardsOwningChunks() const {
+    if (_routingInfo->cm()) {
+        return _routingInfo->cm()->getNShardsOwningChunks();
+    }
+
+    return 0;
+}
+
 Status ChunkManagerTargeter::_refreshShardVersionNow(OperationContext* opCtx) {
     Grid::get(opCtx)->catalogCache()->onStaleShardVersion(std::move(*_routingInfo));
 
diff --git a/src/mongo/s/write_ops/chunk_manager_targeter.h b/src/mongo/s/write_ops/chunk_manager_targeter.h
index e50bd2b1c24..ef8e2c6f8d2 100644
--- a/src/mongo/s/write_ops/chunk_manager_targeter.h
+++ b/src/mongo/s/write_ops/chunk_manager_targeter.h
@@ -111,6 +111,8 @@ public:
      */
     Status refreshIfNeeded(OperationContext* opCtx, bool* wasChanged) override;
 
+    int getNShardsOwningChunks() const override;
+
 private:
     using ShardVersionMap = std::map<ShardId, ChunkVersion>;
 
diff --git a/src/mongo/s/write_ops/mock_ns_targeter.h b/src/mongo/s/write_ops/mock_ns_targeter.h
index 210406d327d..959ac03086e 100644
--- a/src/mongo/s/write_ops/mock_ns_targeter.h
+++ b/src/mongo/s/write_ops/mock_ns_targeter.h
@@ -137,6 +137,11 @@ public:
         return Status::OK();
     }
 
+    int getNShardsOwningChunks() const override {
+        // No-op
+        return 0;
+    }
+
 private:
     static ChunkRange _parseRange(const BSONObj& query) {
         const StringData fieldName(query.firstElement().fieldName());