feat: support dry run execution with EXPLAIN

mc2mc/internal/client/odps.go

@@ -39,8 +39,7 @@ func NewODPSClient(logger *slog.Logger, client *odps.Odps) *odpsClient {
 // when context is cancelled.
 func (c *odpsClient) ExecSQL(ctx context.Context, query string, additionalHints map[string]string) error {
 	if c.isDryRun {
-		c.logger.Info("dry run mode, skipping execution")
-		return nil
+		c.logger.Info("[DRY-RUN] running query in dry-run mode with EXPLAIN.")
 	}
 
 	hints := addHints(additionalHints, query)

mc2mc/mc2mc.go

@@ -17,7 +17,7 @@ import (
 	"github.com/goto/transformers/mc2mc/internal/client"
 	"github.com/goto/transformers/mc2mc/internal/config"
 	"github.com/goto/transformers/mc2mc/internal/logger"
-	"github.com/goto/transformers/mc2mc/internal/query"
+	"github.com/goto/transformers/mc2mc/pkg/query"
 )
 
 func mc2mc(envs []string) error {
@@ -84,6 +84,7 @@ func mc2mc(envs []string) error {
 			query.WithPartitionValue(cfg.DevEnablePartitionValue == "true"),
 			query.WithCostAttributionLabel(cfg.CostAttributionTeam),
 			query.WithColumnOrder(),
+			query.WithDryRun(cfg.DryRun),
 		).Build()
 		if err != nil {
 			return errors.WithStack(err)
@@ -100,6 +101,7 @@ func mc2mc(envs []string) error {
 			query.WithPartitionValue(cfg.DevEnablePartitionValue == "true"),
 			query.WithCostAttributionLabel(cfg.CostAttributionTeam),
 			query.WithColumnOrder(),
+			query.WithDryRun(cfg.DryRun),
 		)
 
 		// -- TODO(START): refactor this part --
@@ -155,6 +157,7 @@ func mc2mc(envs []string) error {
 			query.WithQuery(string(raw)),
 			query.WithCostAttributionLabel(cfg.CostAttributionTeam),
 			query.WithMethod(query.MERGE),
+			query.WithDryRun(cfg.DryRun),
 		).Build()
 		if err != nil {
 			return errors.WithStack(err)

mc2mc/internal/query/builder.go → mc2mc/pkg/query/builder.go

@@ -30,6 +30,7 @@ type Builder struct {
 
 	enableAutoPartition  bool
 	enablePartitionValue bool
+	enableDryRun         bool
 }
 
 // NewBuilder creates a new query builder with the given options
@@ -68,12 +69,6 @@ func (b *Builder) Build() (string, error) {
 	if b.method == MERGE {
 		// split query components
 		hrs, vars, queries := SplitQueryComponents(b.query)
-		if len(queries) <= 1 {
-			if b.costAttributionTeam != "" {
-				return fmt.Sprintf("%s\n%s", b.query, getCostAttributionComment(b.costAttributionTeam)), nil
-			}
-			return b.query, nil
-		}
 		query := b.constructMergeQuery(hrs, vars, queries)
 		return query, nil
 	}
@@ -141,18 +136,30 @@ func (b *Builder) Build() (string, error) {
 		}
 	}
 
+	if b.enableDryRun {
+		// append explain to the query for dry run
+		query = fmt.Sprintf("EXPLAIN\n%s", query)
+	}
+
 	// construct final query with headers, drops, variables and udfs
 	if hr != "" {
 		hr += "\n"
 	}
-	if drops != "" {
-		drops += "\n"
+	dropsStr := ""
+	if len(drops) > 0 {
+		if b.enableDryRun {
+			for i, drop := range drops {
+				drops[i] = fmt.Sprintf("EXPLAIN\n%s", drop)
+			}
+		}
+		dropsStr = strings.Join(drops, "\n;\n")
+		dropsStr += "\n;\n"
 	}
 	if varsAndUDFs != "" {
 		varsAndUDFs += "\n"
 	}
 
-	query = fmt.Sprintf("%s%s%s%s", hr, drops, varsAndUDFs, query)
+	query = fmt.Sprintf("%s%s%s%s", hr, dropsStr, varsAndUDFs, query)
 	if b.costAttributionTeam != "" {
 		query = fmt.Sprintf("%s\n%s\n", query, getCostAttributionComment(b.costAttributionTeam))
 	}
@@ -201,6 +208,14 @@ func (b *Builder) constructOverridedValues(query string) (string, error) {
 
 // constructMergeQueries constructs merge queries with headers and variables
 func (b *Builder) constructMergeQuery(hrs, vars, queries []string) string {
+	if !b.enableDryRun && len(queries) == 1 {
+		// maintaining existing logic for single query
+		if b.costAttributionTeam != "" {
+			return fmt.Sprintf("%s\n%s", b.query, getCostAttributionComment(b.costAttributionTeam))
+		}
+		return b.query
+	}
+
 	builder := strings.Builder{}
 	for i, q := range queries {
 		q = strings.TrimSpace(q)
@@ -215,6 +230,10 @@ func (b *Builder) constructMergeQuery(hrs, vars, queries []string) string {
 		if variables != "" && !IsDDL(q) { // skip variables if it's ddl
 			builder.WriteString(fmt.Sprintf("%s\n", variables))
 		}
+		if b.enableDryRun {
+			// append explain to the DDL query part
+			builder.WriteString("EXPLAIN\n")
+		}
 		builder.WriteString(fmt.Sprintf("%s\n;", q))
 		if b.costAttributionTeam != "" {
 			builder.WriteString(fmt.Sprintf("\n%s\n", getCostAttributionComment(b.costAttributionTeam)))