Group by in Coordinator SHOW

pkg/clientinteractor/interactor.go

@@ -85,6 +85,9 @@ const TEXTOID = 25
 // DOUBLEOID https://github.com/postgres/postgres/blob/master/src/include/catalog/pg_type.dat#L223
 const DOUBLEOID = 701
 
+// INTOID https://github.com/postgres/postgres/blob/master/src/include/catalog/pg_type.dat#L55
+const INTOID = 20
+
 // TODO : unit tests
 
 // TextOidFD generates a pgproto3.FieldDescription object with the provided statement text.
@@ -106,6 +109,13 @@ func TextOidFD(stmt string) pgproto3.FieldDescription {
 	}
 }
 
+// FloatOidFD generates a pgproto3.FieldDescription object of FLOAT8 type with the provided statement text.
+//
+// Parameters:
+// - stmt (string): The statement text to use in the FieldDescription.
+//
+// Returns:
+// - A pgproto3.FieldDescription object initialized with the provided statement text and default values.
 func FloatOidFD(stmt string) pgproto3.FieldDescription {
 	return pgproto3.FieldDescription{
 		Name:                 []byte(stmt),
@@ -118,6 +128,25 @@ func FloatOidFD(stmt string) pgproto3.FieldDescription {
 	}
 }
 
+// IntOidFD generates a pgproto3.FieldDescription object of INT type with the provided statement text.
+//
+// Parameters:
+// - stmt (string): The statement text to use in the FieldDescription.
+//
+// Returns:
+// - A pgproto3.FieldDescription object initialized with the provided statement text and default values.
+func IntOidFD(stmt string) pgproto3.FieldDescription {
+	return pgproto3.FieldDescription{
+		Name:                 []byte(stmt),
+		TableOID:             0,
+		TableAttributeNumber: 0,
+		DataTypeOID:          INTOID,
+		DataTypeSize:         8,
+		TypeModifier:         -1,
+		Format:               0,
+	}
+}
+
 // TODO : unit tests
 
 // WriteHeader sends the row description message with the specified field descriptions.
@@ -1298,32 +1327,58 @@ func (pi *PSQLInteractor) KillClient(clientID uint) error {
 // BackendConnections writes backend connection information to the PSQL client.
 //
 // Parameters:
-// - ctx (context.Context): The context for the operation.
+// - _ (context.Context): The context for the operation.
 // - shs ([]shard.Shardinfo): The list of shard information.
+// - stmt (*spqrparser.Show): The query itself.
 //
 // Returns:
 // - error: An error if any occurred during the operation.
-func (pi *PSQLInteractor) BackendConnections(ctx context.Context, shs []shard.Shardinfo) error {
-	if err := pi.WriteHeader("backend connection id", "router", "shard key name", "hostname", "pid", "user", "dbname", "sync", "tx_served", "tx status"); err != nil {
-		spqrlog.Zero.Error().Err(err).Msg("")
-		return err
-	}
-
-	for _, sh := range shs {
-		router := "no data"
-		s, ok := sh.(shard.CoordShardinfo)
-		if ok {
-			router = s.Router()
-		}
-
-		if err := pi.WriteDataRow(fmt.Sprintf("%d", sh.ID()), router, sh.ShardKeyName(), sh.InstanceHostname(), fmt.Sprintf("%d", sh.Pid()), sh.Usr(), sh.DB(), strconv.FormatInt(sh.Sync(), 10), strconv.FormatInt(sh.TxServed(), 10), sh.TxStatus().String()); err != nil {
+func (pi *PSQLInteractor) BackendConnections(_ context.Context, shs []shard.Shardinfo, stmt *spqrparser.Show) error {
+	headers := []string{"backend connection id", "router", "shard key name", "hostname", "pid", "user", "dbname", "sync", "tx_served", "tx status"}
+	getters := []func(sh shard.Shardinfo) string{
+		func(sh shard.Shardinfo) string { return fmt.Sprintf("%d", sh.ID()) },
+		func(sh shard.Shardinfo) string {
+			router := "no data"
+			s, ok := sh.(shard.CoordShardinfo)
+			if ok {
+				router = s.Router()
+			}
+			return router
+		},
+		func(sh shard.Shardinfo) string { return sh.ShardKeyName() },
+		func(sh shard.Shardinfo) string { return sh.InstanceHostname() },
+		func(sh shard.Shardinfo) string { return fmt.Sprintf("%d", sh.Pid()) },
+		func(sh shard.Shardinfo) string { return sh.Usr() },
+		func(sh shard.Shardinfo) string { return sh.DB() },
+		func(sh shard.Shardinfo) string { return strconv.FormatInt(sh.Sync(), 10) },
+		func(sh shard.Shardinfo) string { return strconv.FormatInt(sh.TxServed(), 10) },
+		func(sh shard.Shardinfo) string { return sh.TxStatus().String() },
+	}
+
+	switch gb := stmt.GroupBy.(type) {
+	case spqrparser.GroupBy:
+		return groupBy(headers, shs, getters, gb.Col.ColName, pi)
+	case spqrparser.GroupByClauseEmpty:
+		if err := pi.WriteHeader(headers...); err != nil {
 			spqrlog.Zero.Error().Err(err).Msg("")
 			return err
 		}
 
-	}
+		for _, sh := range shs {
+			vals := make([]string, 0)
+			for _, getter := range getters {
+				vals = append(vals, getter(sh))
+			}
+			if err := pi.WriteDataRow(vals...); err != nil {
+				spqrlog.Zero.Error().Err(err).Msg("")
+				return err
+			}
+		}
 
-	return pi.CompleteMsg(len(shs))
+		return pi.CompleteMsg(len(shs))
+	default:
+		return spqrerror.NewByCode(spqrerror.SPQR_INVALID_REQUEST)
+	}
 }
 
 // TODO unit tests
@@ -1408,3 +1463,32 @@ func (pi *PSQLInteractor) PreparedStatements(ctx context.Context, shs []shard.Pr
 
 	return pi.CompleteMsg(len(shs))
 }
+
+func groupBy[T any](headers []string, values []T, getters []func(s T) string, groupByCol string, pi *PSQLInteractor) error {
+	ind := -1
+	for i, header := range headers {
+		if header == groupByCol {
+			if err := pi.cl.Send(&pgproto3.RowDescription{
+				Fields: []pgproto3.FieldDescription{TextOidFD(groupByCol), IntOidFD("count")},
+			}); err != nil {
+				spqrlog.Zero.Error().Err(err).Msg("Could not write header for backend connections")
+				return err
+			}
+			ind = i
+			break
+		}
+	}
+
+	cnt := make(map[string]int)
+	for _, value := range values {
+		cnt[getters[ind](value)]++
+	}
+
+	for k, v := range cnt {
+		if err := pi.WriteDataRow(k, fmt.Sprintf("%d", v)); err != nil {
+			return err
+		}
+	}
+
+	return pi.CompleteMsg(len(cnt))
+}

pkg/meta/meta.go

@@ -455,7 +455,7 @@ func ProcessShow(ctx context.Context, stmt *spqrparser.Show, mngr EntityMgr, ci
 			return err
 		}
 
-		return cli.BackendConnections(ctx, resp)
+		return cli.BackendConnections(ctx, resp, stmt)
 	case spqrparser.ShardsStr:
 		shards, err := mngr.ListShards(ctx)
 		if err != nil {

test/feature/features/coordinator_show.feature

@@ -313,6 +313,61 @@ Feature: Coordinator show clients, pools and backend_connections
         ]
         """
 
+    Scenario: 'show backend_connections group by hostname' works 
+        When I run SQL on host "coordinator"
+        """
+        SHOW backend_connections group by hostname
+        """
+        Then command return code should be "0"
+        And SQL result should match json
+        """
+        [
+            {
+                "hostname":"spqr_shard_1:6432",
+                "count": 2
+            }
+        ]
+        """
+        And SQL result should match json
+        """
+        [
+            {
+                "hostname":"spqr_shard_2:6432",
+                "count": 2
+            }
+        ]
+        """
+
+        When I run SQL on host "coordinator"
+        """
+        SHOW backend_connections group by user
+        """
+        Then command return code should be "0"
+        And SQL result should match json
+        """
+        [
+            {
+                "user":"regress",
+                "count": 4
+            }
+        ]
+        """
+
+        When I run SQL on host "coordinator"
+        """
+        SHOW backend_connections group by dbname
+        """
+        Then command return code should be "0"
+        And SQL result should match json
+        """
+        [
+            {
+                "dbname":"regress",
+                "count": 4
+            }
+        ]
+        """
+
     Scenario: show pools works
         When I run SQL on host "coordinator"
         """

yacc/console/ast.go

@@ -23,6 +23,17 @@ type Order struct {
 	Col        ColumnRef
 }
 
+type GroupByClause interface{}
+
+type GroupByClauseEmpty struct {
+	GroupByClause
+}
+
+type GroupBy struct {
+	GroupByClause
+	Col ColumnRef
+}
+
 type WhereClauseNode interface {
 }
 
@@ -47,9 +58,10 @@ type WhereClauseOp struct {
 }
 
 type Show struct {
-	Cmd   string
-	Where WhereClauseNode
-	Order OrderClause
+	Cmd     string
+	Where   WhereClauseNode
+	Order   OrderClause
+	GroupBy GroupByClause
 }
 
 type Set struct {