diff --git a/src/graph/planner/Planner.h b/src/graph/planner/Planner.h
index ec207774491..49238ee1735 100644
--- a/src/graph/planner/Planner.h
+++ b/src/graph/planner/Planner.h
@@ -36,17 +36,28 @@ struct MatchAndInstantiate {
   PlannerInstantiateFunc instantiate;
 };
 
+// A planner generates plans for statements.
+// For example, we have MatchPlanner that generates plan for Match statement.
+// And we have GoPlanner that generates plan for Go statements. Each planner
+// will be registered into the plannersMap in the PlannersRegister when the
+// graphd service starts up.
 class Planner {
  public:
   virtual ~Planner() = default;
 
+  // Each statement might have many planners that match different situations.
+  // Each planner should provide two funtions:
+  // 1. MatchFunc that matchs the proper situation
+  // 2. PlannerInstantiateFunc that instantiates the planner
   static auto& plannersMap() {
     static std::unordered_map<Sentence::Kind, std::vector<MatchAndInstantiate>> plannersMap;
     return plannersMap;
   }
 
+  // Generates plans for each statement based on AsrContext.
   static StatusOr<SubPlan> toPlan(AstContext* astCtx);
 
+  // Transforms the AstContext to a plan which determined by the implementations.
   virtual StatusOr<SubPlan> transform(AstContext* astCtx) = 0;
 
  protected:
diff --git a/src/graph/planner/match/ArgumentFinder.h b/src/graph/planner/match/ArgumentFinder.h
index 381bf210254..1c7a31d3ba5 100644
--- a/src/graph/planner/match/ArgumentFinder.h
+++ b/src/graph/planner/match/ArgumentFinder.h
@@ -10,6 +10,8 @@
 
 namespace nebula {
 namespace graph {
+// ArgumentFinder finds if a pattern uses a named alias that has already been declared
+// in former patterns.
 class ArgumentFinder final : public StartVidFinder {
  public:
   static std::unique_ptr<ArgumentFinder> make() {
diff --git a/src/graph/planner/match/LabelIndexSeek.h b/src/graph/planner/match/LabelIndexSeek.h
index 932d3b7197d..24f6b550d23 100644
--- a/src/graph/planner/match/LabelIndexSeek.h
+++ b/src/graph/planner/match/LabelIndexSeek.h
@@ -11,10 +11,7 @@
 namespace nebula {
 namespace graph {
 
-/*
- * The LabelIndexSeek was designed to find if could get the starting vids by tag
- * index.
- */
+// The LabelIndexSeek finds if a plan could get the starting vids by tag index.
 class LabelIndexSeek final : public StartVidFinder {
  public:
   static std::unique_ptr<LabelIndexSeek> make() {
diff --git a/src/graph/planner/match/MatchClausePlanner.h b/src/graph/planner/match/MatchClausePlanner.h
index 446b7a8131e..e7c08e281bf 100644
--- a/src/graph/planner/match/MatchClausePlanner.h
+++ b/src/graph/planner/match/MatchClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The MatchClausePlanner was designed to generate plan for match clause;
- */
+// The MatchClausePlanner generates plan for match clause;
 class MatchClausePlanner final : public CypherClausePlanner {
  public:
   MatchClausePlanner() = default;
@@ -62,10 +60,8 @@ class MatchClausePlanner final : public CypherClausePlanner {
                         size_t startIndex,
                         SubPlan& subplan);
 
-  /*
-   * Project all named alias.
-   * TODO: Might not neccessary
-   */
+  // Project all named alias.
+  // TODO: Might not neccessary
   Status projectColumnsBySymbols(MatchClauseContext* matchClauseCtx, SubPlan& plan);
 
   YieldColumn* buildVertexColumn(MatchClauseContext* matchClauseCtx,
diff --git a/src/graph/planner/match/MatchPlanner.h b/src/graph/planner/match/MatchPlanner.h
index 0017ee66db3..7ce142dfe6d 100644
--- a/src/graph/planner/match/MatchPlanner.h
+++ b/src/graph/planner/match/MatchPlanner.h
@@ -11,6 +11,7 @@
 
 namespace nebula {
 namespace graph {
+// MatchPlanner generates plans for Match statement based on AstContext.
 class MatchPlanner final : public Planner {
  public:
   static std::unique_ptr<MatchPlanner> make() {
diff --git a/src/graph/planner/match/OrderByClausePlanner.h b/src/graph/planner/match/OrderByClausePlanner.h
index de6c0859311..fbb892cda53 100644
--- a/src/graph/planner/match/OrderByClausePlanner.h
+++ b/src/graph/planner/match/OrderByClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The OrderByClausePlanner was designed to generate plan for order by clause;
- */
+// The OrderByClausePlanner generates plan for order by clause;
 class OrderByClausePlanner final : public CypherClausePlanner {
  public:
   OrderByClausePlanner() = default;
diff --git a/src/graph/planner/match/PaginationPlanner.h b/src/graph/planner/match/PaginationPlanner.h
index c76bb9981f3..3cad9ab2a7a 100644
--- a/src/graph/planner/match/PaginationPlanner.h
+++ b/src/graph/planner/match/PaginationPlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The PaginationPlanner was designed to generate subplan for skip/limit clause.
- */
+// The PaginationPlanner generates subplan for skip/limit clause.
 class PaginationPlanner final : public CypherClausePlanner {
  public:
   PaginationPlanner() = default;
diff --git a/src/graph/planner/match/PropIndexSeek.h b/src/graph/planner/match/PropIndexSeek.h
index e83c65e600a..821178e1615 100644
--- a/src/graph/planner/match/PropIndexSeek.h
+++ b/src/graph/planner/match/PropIndexSeek.h
@@ -10,10 +10,8 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The PropIndexSeek was designed to find if could get starting vids by tag
- * props or edge props index.
- */
+// The PropIndexSeek finds if a plan could get starting vids by tag
+// props or edge props index.
 class PropIndexSeek final : public StartVidFinder {
  public:
   static std::unique_ptr<PropIndexSeek> make() {
diff --git a/src/graph/planner/match/ReturnClausePlanner.h b/src/graph/planner/match/ReturnClausePlanner.h
index 4431a2a7c7a..e93f741af4b 100644
--- a/src/graph/planner/match/ReturnClausePlanner.h
+++ b/src/graph/planner/match/ReturnClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The ReturnClausePlanner was designed to generated plan for return clause.
- */
+// The ReturnClausePlanner generates plan for return clause.
 class ReturnClausePlanner final : public CypherClausePlanner {
  public:
   ReturnClausePlanner() = default;
diff --git a/src/graph/planner/match/ScanSeek.h b/src/graph/planner/match/ScanSeek.h
index 1142723d974..c07243d8a7f 100644
--- a/src/graph/planner/match/ScanSeek.h
+++ b/src/graph/planner/match/ScanSeek.h
@@ -11,10 +11,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The ScanSeek was designed to find if could get the starting vids in
- * filter.
- */
+// The ScanSeek finds if a plan could get the starting vids in filter.
 class ScanSeek final : public StartVidFinder {
  public:
   static std::unique_ptr<ScanSeek> make() {
diff --git a/src/graph/planner/match/SegmentsConnector.h b/src/graph/planner/match/SegmentsConnector.h
index 1594879c348..29bf4ff8bfd 100644
--- a/src/graph/planner/match/SegmentsConnector.h
+++ b/src/graph/planner/match/SegmentsConnector.h
@@ -13,10 +13,7 @@
 
 namespace nebula {
 namespace graph {
-/**
- * The SegmentsConnector was designed to be a util to help connecting the
- * plan segment.
- */
+// The SegmentsConnector is a util to help connecting the plan segment.
 class SegmentsConnector final {
  public:
   SegmentsConnector() = delete;
diff --git a/src/graph/planner/match/StartVidFinder.h b/src/graph/planner/match/StartVidFinder.h
index 7a740fd57d9..bc841274e71 100644
--- a/src/graph/planner/match/StartVidFinder.h
+++ b/src/graph/planner/match/StartVidFinder.h
@@ -15,6 +15,27 @@ class StartVidFinder;
 
 using StartVidFinderInstantiateFunc = std::function<std::unique_ptr<StartVidFinder>()>;
 
+// A StartVidFinder finds a generally good solution for traversing from the vids.
+// Currently we have five StartVidFinders:
+// 1. VertexIdSeek find if a plan could traverse from a given vid.
+// MATCH(n) WHERE id(n) = value RETURN n
+//
+// 2. ArgumentFinder finds if a plan could traverse from some vids that already
+// beed traversed.
+// MATCH (n)-[]-(l), (l)-[]-(m) return n,l,m
+// MATCH (n)-[]-(l) MATCH (l)-[]-(m) return n,l,m
+//
+// 3. PropIndexSeek finds if a plan could traverse from some vids that could be
+// read from the property indices.
+// MATCH(n:Tag{prop:value}) RETURN n
+// MATCH(n:Tag) WHERE n.prop = value RETURN n
+//
+// 4. LabelIndexSeek finds if a plan could traverse from some vids that could be
+// read from the label indices.
+// MATCH(n: tag) RETURN n
+// MATCH(s)-[:edge]->(e) RETURN e
+//
+// 5. ScanSeek finds if a plan could traverse from some vids by scanning.
 class StartVidFinder {
  public:
   virtual ~StartVidFinder() = default;
@@ -26,8 +47,12 @@ class StartVidFinder {
 
   bool match(PatternContext* patternCtx);
 
+  // The derived class should implement matchNode if the finder has
+  // the ability to find vids from node pattern.
   virtual bool matchNode(NodeContext* nodeCtx) = 0;
 
+  // The derived class should implement matchEdge if the finder has
+  // the ability to find vids from edge pattern.
   virtual bool matchEdge(EdgeContext* nodeCtx) = 0;
 
   StatusOr<SubPlan> transform(PatternContext* patternCtx);
diff --git a/src/graph/planner/match/UnwindClausePlanner.h b/src/graph/planner/match/UnwindClausePlanner.h
index 46b0f8777bd..36f21afe133 100644
--- a/src/graph/planner/match/UnwindClausePlanner.h
+++ b/src/graph/planner/match/UnwindClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The UnwindClausePlanner was designed to generate plan for unwind clause
- */
+// The UnwindClausePlanner generates plan for unwind clause
 class UnwindClausePlanner final : public CypherClausePlanner {
  public:
   UnwindClausePlanner() = default;
diff --git a/src/graph/planner/match/VertexIdSeek.h b/src/graph/planner/match/VertexIdSeek.h
index 2fd58a172aa..b3ea83d5f60 100644
--- a/src/graph/planner/match/VertexIdSeek.h
+++ b/src/graph/planner/match/VertexIdSeek.h
@@ -11,10 +11,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The VertexIdSeek was designed to find if could get the starting vids in
- * filter.
- */
+// The VertexIdSeek find if a plan could get the starting vids in filters.
 class VertexIdSeek final : public StartVidFinder {
  public:
   static std::unique_ptr<VertexIdSeek> make() {
diff --git a/src/graph/planner/match/WhereClausePlanner.h b/src/graph/planner/match/WhereClausePlanner.h
index c9a04e4c607..3a68b057f7e 100644
--- a/src/graph/planner/match/WhereClausePlanner.h
+++ b/src/graph/planner/match/WhereClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The WhereClausePlanner was designed to generate plan for where clause.
- */
+// The WhereClausePlanner generates plan for where clause.
 class WhereClausePlanner final : public CypherClausePlanner {
  public:
   explicit WhereClausePlanner(bool needStableFilter = false)
diff --git a/src/graph/planner/match/WithClausePlanner.h b/src/graph/planner/match/WithClausePlanner.h
index 812cba8ba19..4e481e8179b 100644
--- a/src/graph/planner/match/WithClausePlanner.h
+++ b/src/graph/planner/match/WithClausePlanner.h
@@ -10,9 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The WithClausePlanner was designed to generate plan for with clause.
- */
+// The WithClausePlanner generates plan for with clause.
 class WithClausePlanner final : public CypherClausePlanner {
  public:
   WithClausePlanner() = default;
diff --git a/src/graph/planner/match/YieldClausePlanner.h b/src/graph/planner/match/YieldClausePlanner.h
index 725335f5758..9260335532e 100644
--- a/src/graph/planner/match/YieldClausePlanner.h
+++ b/src/graph/planner/match/YieldClausePlanner.h
@@ -10,10 +10,7 @@
 
 namespace nebula {
 namespace graph {
-/*
- * The YieldClausePlanner was designed to generate plan for yield clause in
- * cypher
- */
+// The YieldClausePlanner generates plan for yield clause
 class YieldClausePlanner final : public CypherClausePlanner {
  public:
   YieldClausePlanner() = default;
diff --git a/src/graph/planner/ngql/GoPlanner.cpp b/src/graph/planner/ngql/GoPlanner.cpp
index 9142e40960c..8f7215b7bb0 100644
--- a/src/graph/planner/ngql/GoPlanner.cpp
+++ b/src/graph/planner/ngql/GoPlanner.cpp
@@ -90,11 +90,8 @@ Expression* GoPlanner::loopCondition(uint32_t steps, const std::string& var) {
   return LogicalExpression::makeAnd(pool, step, earlyEnd);
 }
 
-/*
- * extract vid and edge's prop from GN
- * for joinDst & joinInput
- * output colNames {srcProps, edgeProps, kVid, "JOIN_DST_VID"}
- */
+// Extracts vid and edge's prop from GN for joinDst & joinInput.
+// The root plan node will output colNames of {srcProps, edgeProps, kVid, "JOIN_DST_VID"}.
 PlanNode* GoPlanner::extractSrcEdgePropsFromGN(PlanNode* dep, const std::string& input) {
   auto& srcEdgePropsExpr = goCtx_->srcEdgePropsExpr;
   auto* pool = goCtx_->qctx->objPool();
@@ -116,11 +113,8 @@ PlanNode* GoPlanner::extractSrcEdgePropsFromGN(PlanNode* dep, const std::string&
   return project;
 }
 
-/*
- * extract vid and dst from GN
- * for trackStartVid
- * output ColNames {srcVidColName, "TRACK_DST_VID"}
- */
+// Extracts vid and dst from GN for trackStartVid.
+// The root plan node will output ColNames of {srcVidColName, "TRACK_DST_VID"}.
 PlanNode* GoPlanner::extractSrcDstFromGN(PlanNode* dep, const std::string& input) {
   auto qctx = goCtx_->qctx;
   auto* pool = qctx->objPool();
@@ -138,11 +132,8 @@ PlanNode* GoPlanner::extractSrcDstFromGN(PlanNode* dep, const std::string& input
   return dedup;
 }
 
-/*
- * extract vid from runTime input
- * for joinInput
- * output ColNames {runtimeVidName, dstVidColName}
- */
+// Extracts vid from runTime input for joinInput.
+// The root plan node will output ColNames of {runtimeVidName, dstVidColName}.
 PlanNode* GoPlanner::extractVidFromRuntimeInput(PlanNode* dep) {
   if (dep == nullptr) {
     return dep;
@@ -166,13 +157,11 @@ PlanNode* GoPlanner::extractVidFromRuntimeInput(PlanNode* dep) {
   return dedup;
 }
 
-/*
- * establish a mapping between the original vId and the expanded destination vId
- * during each step of the expansion in the n-step and mton-step scenario
- * left: n-1 steps
- * right: step n
- * output ColNames {runtimeVidName, dstVidColName}
- */
+// Establishes a mapping between the original vId and the expanded destination vId
+// during each step of the expansion in the n-step and mton-step scenario.
+// The root plan node will output ColNames of {runtimeVidName, dstVidColName}.
+// left: (n-1)th step
+// right: (n)th step
 PlanNode* GoPlanner::trackStartVid(PlanNode* left, PlanNode* right) {
   auto qctx = goCtx_->qctx;
   auto* pool = qctx->objPool();
@@ -207,10 +196,8 @@ PlanNode* GoPlanner::trackStartVid(PlanNode* left, PlanNode* right) {
   return dedup;
 }
 
-/*
- * output ColNames {srcProps, edgeProps, kVid, "JOIN_DST_VID", "DST_VID",
- * dstProps}
- */
+// The root plan node will output ColNames of
+// {srcProps, edgeProps, kVid, "JOIN_DST_VID", "DST_VID", dstProps}
 PlanNode* GoPlanner::buildJoinDstPlan(PlanNode* dep) {
   auto qctx = goCtx_->qctx;
   auto* pool = qctx->objPool();
@@ -279,11 +266,10 @@ PlanNode* GoPlanner::buildJoinInputPlan(PlanNode* dep) {
   return join;
 }
 
-/*
- * left's colName dstVidColName join right's colName kVid
- * left  : n-1 steps
- * right : last step
- */
+// The column named as dstVidColName of the left plan node join on the column named as kVid of the
+// right one.
+// left  : (n-1)th step
+// right : last step
 PlanNode* GoPlanner::lastStepJoinInput(PlanNode* left, PlanNode* right) {
   auto qctx = goCtx_->qctx;
   auto* pool = qctx->objPool();
@@ -374,8 +360,7 @@ PlanNode* GoPlanner::buildSampleLimitImpl(PlanNode* input, T sampleLimit) {
   return node;
 }
 
-// generate
-// $limits[$step-1]
+// Generates $limits[$step-1]
 Expression* GoPlanner::stepSampleLimit() {
   auto qctx = goCtx_->qctx;
   // $limits
diff --git a/src/graph/planner/ngql/PathPlanner.cpp b/src/graph/planner/ngql/PathPlanner.cpp
index 297d749d936..1d18be5b45a 100644
--- a/src/graph/planner/ngql/PathPlanner.cpp
+++ b/src/graph/planner/ngql/PathPlanner.cpp
@@ -469,29 +469,29 @@ PlanNode* PathPlanner::buildEdgePlan(PlanNode* dep, const std::string& input) {
   return getEdge;
 }
 
-/*
-          The Plan looks like this:
-                 +--------+---------+
-             +-->+   PassThrough    +<----+
-             |   +------------------+     |
-    +--------+---------+        +---------+------------+
-    |  Project(Nodes)  |        |Project(RelationShips)|
-    +--------+---------+        +---------+------------+
-             |                            |
-    +--------+---------+        +---------+--------+
-    |      Unwind      |        |      Unwind      |
-    +--------+---------+        +---------+--------+
-             |                            |
-    +--------+---------+        +---------+--------+
-    |   GetVertices    |        |    GetEdges      |
-    +--------+---------+        +---------+--------+
-             |                            |
-             +------------+---------------+
-                          |
-                 +--------+---------+
-                 |   DataCollect    |
-                 +--------+---------+
-*/
+//
+//        The Plan looks like this:
+//               +--------+---------+
+//           +-->+   PassThrough    +<----+
+//           |   +------------------+     |
+//  +--------+---------+        +---------+------------+
+//  |  Project(Nodes)  |        |Project(RelationShips)|
+//  +--------+---------+        +---------+------------+
+//           |                            |
+//  +--------+---------+        +---------+--------+
+//  |      Unwind      |        |      Unwind      |
+//  +--------+---------+        +---------+--------+
+//           |                            |
+//  +--------+---------+        +---------+--------+
+//  |   GetVertices    |        |    GetEdges      |
+//  +--------+---------+        +---------+--------+
+//           |                            |
+//           +------------+---------------+
+//                        |
+//               +--------+---------+
+//               |   DataCollect    |
+//               +--------+---------+
+//
 PlanNode* PathPlanner::buildPathProp(PlanNode* dep) {
   auto qctx = pathCtx_->qctx;
   auto* pt = PassThroughNode::make(qctx, dep);
diff --git a/src/graph/planner/plan/Admin.h b/src/graph/planner/plan/Admin.h
index d9204647c02..2fd3526fc0b 100644
--- a/src/graph/planner/plan/Admin.h
+++ b/src/graph/planner/plan/Admin.h
@@ -10,12 +10,10 @@
 #include "graph/planner/plan/Query.h"
 #include "interface/gen-cpp2/meta_types.h"
 
-/**
- * All admin-related nodes would be put in this file.
- * These nodes would not exist in a same plan with maintain-related/
- * mutate-related/query-related nodes. And they are also isolated
- * from each other. This would be guaranteed by parser and validator.
- */
+// All admin-related nodes would be put in this file.
+// These nodes would not exist in a same plan with maintain-related/
+// mutate-related/query-related nodes. And they are also isolated
+// from each other. This would be guaranteed by parser and validator.
 namespace nebula {
 namespace graph {
 
diff --git a/src/graph/planner/plan/ExecutionPlan.h b/src/graph/planner/plan/ExecutionPlan.h
index 86bfe10cbbd..469a7ed4b89 100644
--- a/src/graph/planner/plan/ExecutionPlan.h
+++ b/src/graph/planner/plan/ExecutionPlan.h
@@ -23,6 +23,7 @@ struct SubPlan {
   PlanNode* tail{nullptr};
 };
 
+// An ExecutionPlan is a Directed Cyclic Graph which composed by PlanNodes.
 class ExecutionPlan final {
  public:
   explicit ExecutionPlan(PlanNode* root = nullptr);
diff --git a/src/graph/planner/plan/Logic.h b/src/graph/planner/plan/Logic.h
index c128031c811..286a2352364 100644
--- a/src/graph/planner/plan/Logic.h
+++ b/src/graph/planner/plan/Logic.h
@@ -11,6 +11,7 @@
 namespace nebula {
 namespace graph {
 
+// StartNode is a spetial leaf node that helps the scheduler to work properly.
 class StartNode final : public PlanNode {
  public:
   static StartNode* make(QueryContext* qctx) {
@@ -47,6 +48,7 @@ class BinarySelect : public SingleInputNode {
   Expression* condition_{nullptr};
 };
 
+// Select the if branch or else branch at runtime
 class Select final : public BinarySelect {
  public:
   static Select* make(QueryContext* qctx,
@@ -92,6 +94,7 @@ class Select final : public BinarySelect {
   PlanNode* else_{nullptr};
 };
 
+// Executing the branch multi times at runtime.
 class Loop final : public BinarySelect {
  public:
   static Loop* make(QueryContext* qctx,
@@ -123,9 +126,7 @@ class Loop final : public BinarySelect {
   PlanNode* body_{nullptr};
 };
 
-/**
- * This operator is used for pass through situation.
- */
+// This operator is used for pass through situation.
 class PassThroughNode final : public SingleInputNode {
  public:
   static PassThroughNode* make(QueryContext* qctx, PlanNode* input) {
@@ -141,9 +142,7 @@ class PassThroughNode final : public SingleInputNode {
   void cloneMembers(const PassThroughNode&);
 };
 
-/**
- * This operator is used for getting a named alias from another executed operator.
- */
+// This operator is used for getting a named alias from another executed operator.
 class Argument final : public PlanNode {
  public:
   static Argument* make(QueryContext* qctx, std::string alias) {
diff --git a/src/graph/planner/plan/Mutate.h b/src/graph/planner/plan/Mutate.h
index f6ffc49ea07..a45d01dff69 100644
--- a/src/graph/planner/plan/Mutate.h
+++ b/src/graph/planner/plan/Mutate.h
@@ -10,9 +10,7 @@
 #include "graph/planner/plan/Query.h"
 #include "parser/TraverseSentences.h"
 
-/**
- * All mutate-related nodes would put in this file.
- */
+// All mutate-related nodes would put in this file.
 namespace nebula {
 namespace graph {
 class InsertVertices final : public SingleDependencyNode {
diff --git a/src/graph/planner/plan/PlanNode.h b/src/graph/planner/plan/PlanNode.h
index 71ea608440d..774e57eed21 100644
--- a/src/graph/planner/plan/PlanNode.h
+++ b/src/graph/planner/plan/PlanNode.h
@@ -16,10 +16,8 @@ namespace graph {
 
 class PlanNodeVisitor;
 
-/**
- * PlanNode is an abstraction of nodes in an execution plan which
- * is a kind of directed cyclic graph.
- */
+// PlanNode is an abstraction of nodes in an execution plan which
+// is a kind of directed cyclic graph.
 class PlanNode {
  public:
   enum class Kind : uint8_t {
@@ -362,6 +360,7 @@ class SingleDependencyNode : public PlanNode {
   std::unique_ptr<PlanNodeDescription> explain() const override;
 };
 
+// SingleInputNode has one dependency and it sinks data from the dependency.
 class SingleInputNode : public SingleDependencyNode {
  public:
   std::unique_ptr<PlanNodeDescription> explain() const override;
@@ -385,6 +384,7 @@ class SingleInputNode : public SingleDependencyNode {
   SingleInputNode(QueryContext* qctx, Kind kind, const PlanNode* dep);
 };
 
+// BinaryInputNode has two dependencies and it sinks data from them.
 class BinaryInputNode : public PlanNode {
  public:
   void setLeftDep(const PlanNode* left) {
diff --git a/src/graph/planner/plan/Query.h b/src/graph/planner/plan/Query.h
index 14d97f7ee38..76ca25acd9c 100644
--- a/src/graph/planner/plan/Query.h
+++ b/src/graph/planner/plan/Query.h
@@ -13,19 +13,15 @@
 #include "parser/Clauses.h"
 #include "parser/TraverseSentences.h"
 
-/**
- * All query-related nodes would be put in this file,
- * and they are derived from PlanNode.
- */
+// All query-related nodes would be put in this file,
+// and they are derived from PlanNode.
 namespace nebula {
 namespace graph {
-/**
- * Now we have four kind of exploration nodes:
- *  GetNeighbors,
- *  GetVertices,
- *  GetEdges,
- *  IndexScan
- */
+// Now we have four kind of exploration nodes:
+//  GetNeighbors,
+//  GetVertices,
+//  GetEdges,
+//  IndexScan
 class Explore : public SingleInputNode {
  public:
   GraphSpaceID space() const {
@@ -137,9 +133,8 @@ using EdgeProp = nebula::storage::cpp2::EdgeProp;
 using StatProp = nebula::storage::cpp2::StatProp;
 using Expr = nebula::storage::cpp2::Expr;
 using Direction = nebula::storage::cpp2::EdgeDirection;
-/**
- * Get neighbors' property
- */
+
+// Get neighbors' property
 class GetNeighbors : public Explore {
  public:
   static GetNeighbors* make(QueryContext* qctx, PlanNode* input, GraphSpaceID space) {
@@ -263,9 +258,7 @@ class GetNeighbors : public Explore {
   bool random_{false};
 };
 
-/**
- * Get property with given vertex keys.
- */
+// Get property with given vertex keys.
 class GetVertices : public Explore {
  public:
   static GetVertices* make(QueryContext* qctx,
@@ -346,9 +339,7 @@ class GetVertices : public Explore {
   std::unique_ptr<std::vector<Expr>> exprs_;
 };
 
-/**
- * Get property with given edge keys.
- */
+// Get property with given edge keys.
 class GetEdges final : public Explore {
  public:
   static GetEdges* make(QueryContext* qctx,
@@ -450,9 +441,7 @@ class GetEdges final : public Explore {
   std::unique_ptr<std::vector<Expr>> exprs_;
 };
 
-/**
- * Read data through the index.
- */
+// Read data through the index.
 class IndexScan : public Explore {
  public:
   using IndexQueryContext = storage::cpp2::IndexQueryContext;
@@ -569,9 +558,7 @@ class IndexScan : public Explore {
   YieldColumns* yieldColumns_;
 };
 
-/**
- * Scan vertices
- */
+// Scan vertices
 class ScanVertices final : public Explore {
  public:
   static ScanVertices* make(QueryContext* qctx,
@@ -636,9 +623,7 @@ class ScanVertices final : public Explore {
   std::unique_ptr<std::vector<Expr>> exprs_;
 };
 
-/**
- * Scan edges
- */
+// Scan edges
 class ScanEdges final : public Explore {
  public:
   static ScanEdges* make(QueryContext* qctx,
@@ -703,9 +688,7 @@ class ScanEdges final : public Explore {
   std::unique_ptr<std::vector<Expr>> exprs_;
 };
 
-/**
- * A Filter node helps filt some records with condition.
- */
+// A Filter node helps filt some records with condition.
 class Filter final : public SingleInputNode {
  public:
   static Filter* make(QueryContext* qctx,
@@ -742,12 +725,10 @@ class Filter final : public SingleInputNode {
   bool needStableFilter_;
 };
 
-/**
- * Now we have three kind of set operations:
- *   UNION,
- *   INTERSECT,
- *   MINUS
- */
+// Now we have three kind of set operations:
+//   UNION,
+//   INTERSECT,
+//   MINUS
 class SetOp : public BinaryInputNode {
  protected:
   SetOp(QueryContext* qctx, Kind kind, PlanNode* left, PlanNode* right)
@@ -758,9 +739,7 @@ class SetOp : public BinaryInputNode {
   void cloneMembers(const SetOp&);
 };
 
-/**
- * Combine two set of records.
- */
+// Combine two set of records.
 class Union final : public SetOp {
  public:
   static Union* make(QueryContext* qctx, PlanNode* left, PlanNode* right) {
@@ -776,9 +755,7 @@ class Union final : public SetOp {
   void cloneMembers(const Union&);
 };
 
-/**
- * Return the intersected records between two sets.
- */
+// Return the intersected records between two sets.
 class Intersect final : public SetOp {
  public:
   static Intersect* make(QueryContext* qctx, PlanNode* left, PlanNode* right) {
@@ -794,9 +771,7 @@ class Intersect final : public SetOp {
   void cloneMembers(const Intersect&);
 };
 
-/**
- * Do subtraction between two sets.
- */
+// Do subtraction between two sets.
 class Minus final : public SetOp {
  public:
   static Minus* make(QueryContext* qctx, PlanNode* left, PlanNode* right) {
@@ -812,9 +787,7 @@ class Minus final : public SetOp {
   void cloneMembers(const Minus&);
 };
 
-/**
- * Project is used to specify output vars or field.
- */
+// Project is used to specify output vars or field.
 class Project final : public SingleInputNode {
  public:
   static Project* make(QueryContext* qctx, PlanNode* input, YieldColumns* cols = nullptr) {
@@ -839,6 +812,7 @@ class Project final : public SingleInputNode {
   YieldColumns* cols_{nullptr};
 };
 
+// Thansforms a list to column.
 class Unwind final : public SingleInputNode {
  public:
   static Unwind* make(QueryContext* qctx,
@@ -870,9 +844,7 @@ class Unwind final : public SingleInputNode {
   std::string alias_;
 };
 
-/**
- * Sort the given record set.
- */
+// Sort the given record set.
 class Sort final : public SingleInputNode {
  public:
   static Sort* make(QueryContext* qctx,
@@ -916,9 +888,7 @@ class Sort final : public SingleInputNode {
   std::vector<std::pair<size_t, OrderFactor::OrderType>> factors_;
 };
 
-/**
- * Output the records with the given limitation.
- */
+// Output the records with the given limitation.
 class Limit final : public SingleInputNode {
  public:
   static Limit* make(QueryContext* qctx, PlanNode* input, int64_t offset = -1, int64_t count = -1) {
@@ -976,9 +946,7 @@ class Limit final : public SingleInputNode {
   Expression* count_{nullptr};
 };
 
-/**
- * Get the Top N record set.
- */
+// Get the Top N record set.
 class TopN final : public SingleInputNode {
  public:
   static TopN* make(QueryContext* qctx,
@@ -1040,9 +1008,7 @@ class TopN final : public SingleInputNode {
   int64_t count_{-1};
 };
 
-/**
- * Sample the given input data.
- */
+// Sample the given input data.
 class Sample final : public SingleInputNode {
  public:
   static Sample* make(QueryContext* qctx, PlanNode* input, const int64_t count) {
@@ -1093,10 +1059,8 @@ class Sample final : public SingleInputNode {
   Expression* count_{nullptr};
 };
 
-/**
- * Do Aggregation with the given set of records,
- * such as AVG(), COUNT()...
- */
+// Do Aggregation with the given set of records,
+// such as AVG(), COUNT()...
 class Aggregate final : public SingleInputNode {
  public:
   static Aggregate* make(QueryContext* qctx,
@@ -1137,6 +1101,7 @@ class Aggregate final : public SingleInputNode {
   std::vector<Expression*> groupItems_;
 };
 
+// Change the space that specified for current session.
 class SwitchSpace final : public SingleInputNode {
  public:
   static SwitchSpace* make(QueryContext* qctx, PlanNode* input, std::string spaceName) {
@@ -1162,6 +1127,7 @@ class SwitchSpace final : public SingleInputNode {
   std::string spaceName_;
 };
 
+// Dedup the rows.
 class Dedup final : public SingleInputNode {
  public:
   static Dedup* make(QueryContext* qctx, PlanNode* input) {
@@ -1176,6 +1142,7 @@ class Dedup final : public SingleInputNode {
   void cloneMembers(const Dedup&);
 };
 
+// Collect the variable results.
 class DataCollect final : public VariableDependencyNode {
  public:
   enum class DCKind : uint8_t {
@@ -1252,6 +1219,8 @@ class DataCollect final : public VariableDependencyNode {
   bool distinct_{false};
 };
 
+// Join two result set based on the keys
+// We have LeftJoin and InnerJoin now.
 class Join : public SingleDependencyNode {
  public:
   const std::pair<std::string, int64_t>& leftVar() const {
@@ -1309,9 +1278,7 @@ class Join : public SingleDependencyNode {
   std::vector<Expression*> probeKeys_;
 };
 
-/*
- *  left join
- */
+// Left join
 class LeftJoin final : public Join {
  public:
   static LeftJoin* make(QueryContext* qctx,
@@ -1349,9 +1316,7 @@ class LeftJoin final : public Join {
   void cloneMembers(const LeftJoin&);
 };
 
-/*
- *  inner join
- */
+// Inner join
 class InnerJoin final : public Join {
  public:
   static InnerJoin* make(QueryContext* qctx,
@@ -1389,9 +1354,7 @@ class InnerJoin final : public Join {
   void cloneMembers(const InnerJoin&);
 };
 
-/*
- * set var = value
- */
+// Binding a value to a variable
 class Assign final : public SingleInputNode {
  public:
   static Assign* make(QueryContext* qctx, PlanNode* input) {
@@ -1421,10 +1384,8 @@ class Assign final : public SingleInputNode {
   std::vector<std::pair<std::string, Expression*>> items_;
 };
 
-/**
- * Union all versions of the variable in the dependency
- * The input is a single PlanNode
- */
+// Union all versions of the variable in the dependency
+// The input is a single PlanNode
 class UnionAllVersionVar final : public SingleInputNode {
  public:
   static UnionAllVersionVar* make(QueryContext* qctx, PlanNode* input) {
@@ -1440,6 +1401,7 @@ class UnionAllVersionVar final : public SingleInputNode {
   void cloneMembers(const UnionAllVersionVar&);
 };
 
+// Traverse several steps based on condition.
 class Traverse final : public GetNeighbors {
  public:
   using VertexProps = std::unique_ptr<std::vector<storage::cpp2::VertexProp>>;
@@ -1535,6 +1497,7 @@ class Traverse final : public GetNeighbors {
   bool trackPrevPath_{true};
 };
 
+// Append vertices to a path.
 class AppendVertices final : public GetVertices {
  public:
   static AppendVertices* make(QueryContext* qctx, PlanNode* input, GraphSpaceID space) {
@@ -1584,6 +1547,7 @@ class AppendVertices final : public GetVertices {
   bool trackPrevPath_{true};
 };
 
+// Binary Join that joins two results from two inputs.
 class BiJoin : public BinaryInputNode {
  public:
   const std::vector<Expression*>& hashKeys() const {
@@ -1621,9 +1585,7 @@ class BiJoin : public BinaryInputNode {
   std::vector<Expression*> probeKeys_;
 };
 
-/*
- *  left join
- */
+// Left join
 class BiLeftJoin final : public BiJoin {
  public:
   static BiLeftJoin* make(QueryContext* qctx,
@@ -1649,9 +1611,7 @@ class BiLeftJoin final : public BiJoin {
   void cloneMembers(const BiLeftJoin&);
 };
 
-/*
- *  inner join
- */
+// Inner join
 class BiInnerJoin final : public BiJoin {
  public:
   static BiInnerJoin* make(QueryContext* qctx,