Return virtual timestamp for scan query (#14001)

Author: dcherednik

include/ydb-cpp-sdk/client/table/table.h

@@ -2063,6 +2063,8 @@ class TReadTableSnapshot {
     uint64_t TxId_;
 };
 
+using TVirtualTimestamp = TReadTableSnapshot;
+
 template<typename TPart>
 class TSimpleStreamPart : public TStreamPartStatus {
 public:
@@ -2117,6 +2119,10 @@ class TScanQueryPart : public TStreamPartStatus {
     const std::string& GetDiagnostics() const { return *Diagnostics_; }
     std::string&& ExtractDiagnostics() { return std::move(*Diagnostics_); }
 
+    bool HasVirtualTimestamp() const { return Vt_.has_value(); }
+    const TVirtualTimestamp& GetVirtualTimestamp() const { return *Vt_; }
+    TVirtualTimestamp&& ExtractVirtualTimestamp() { return std::move(*Vt_); }
+
     TScanQueryPart(TStatus&& status)
         : TStreamPartStatus(std::move(status))
     {}
@@ -2127,17 +2133,20 @@ class TScanQueryPart : public TStreamPartStatus {
         , Diagnostics_(diagnostics)
     {}
 
-    TScanQueryPart(TStatus&& status, TResultSet&& resultSet, const std::optional<TQueryStats>& queryStats, const std::optional<std::string>& diagnostics)
+    TScanQueryPart(TStatus&& status, TResultSet&& resultSet, const std::optional<TQueryStats>& queryStats,
+        const std::optional<std::string>& diagnostics, std::optional<TVirtualTimestamp>&& vt)
         : TStreamPartStatus(std::move(status))
         , ResultSet_(std::move(resultSet))
         , QueryStats_(queryStats)
         , Diagnostics_(diagnostics)
+        , Vt_(std::move(vt))
     {}
 
 private:
     std::optional<TResultSet> ResultSet_;
     std::optional<TQueryStats> QueryStats_;
     std::optional<std::string> Diagnostics_;
+    std::optional<TVirtualTimestamp> Vt_;
 };
 
 using TAsyncScanQueryPart = NThreading::TFuture<TScanQueryPart>;

src/api/protos/ydb_query.proto

@@ -8,6 +8,7 @@ option java_outer_classname = "QueryProtos";
 import "google/protobuf/duration.proto";
 
 import "src/api/protos/annotations/validation.proto";
+import "src/api/protos/ydb_common.proto";
 import "src/api/protos/ydb_issue_message.proto";
 import "src/api/protos/ydb_operation.proto";
 import "src/api/protos/ydb_query_stats.proto";
@@ -200,6 +201,7 @@ message ExecuteQueryResponsePart {
     Ydb.TableStats.QueryStats exec_stats = 5;
 
     TransactionMeta tx_meta = 6;
+    VirtualTimestamp snapshot_timestamp = 7;
 }
 
 message ExecuteScriptRequest {

src/api/protos/ydb_table.proto

@@ -1293,6 +1293,8 @@ message ExecuteScanQueryPartialResult {
     // works only in mode: MODE_EXPLAIN,
     // collects additional diagnostics about query compilation, including query plan and scheme
     string query_full_diagnostics = 7 [deprecated = true];
+    // Optional snapshot that corresponds to the returned data
+    VirtualTimestamp snapshot = 8;
 }
 
 // Returns information about an external data source with a given path.

src/client/table/impl/readers.cpp

@@ -89,9 +89,16 @@ TAsyncScanQueryPart TScanQueryPartIterator::TReaderImpl::ReadNext(std::shared_pt
 
             diagnostics = self->Response_.result().query_full_diagnostics();
 
+            std::optional<TVirtualTimestamp> vt;
+
+            if (self->Response_.result().has_snapshot()) {
+                const auto& snap = self->Response_.result().snapshot();
+                vt = TVirtualTimestamp(snap.plan_step(), snap.tx_id());
+            }
+
             if (self->Response_.result().has_result_set()) {
                 promise.SetValue({std::move(status),
-                    TResultSet(std::move(*self->Response_.mutable_result()->mutable_result_set())), queryStats, diagnostics});
+                    TResultSet(std::move(*self->Response_.mutable_result()->mutable_result_set())), queryStats, diagnostics, std::move(vt)});
             } else {
                 promise.SetValue({std::move(status), queryStats, diagnostics});
             }