feat: implement loader error handling and refactor chunk processing in migration job

cmd/go_migrate/extractor-error-handler.go

@@ -81,20 +81,18 @@ func ExtractorErrorFromLastRowMssql(lastRow UnknownRowValues, indexPrimaryKey in
 	if !ok {
 		currentBatch := *batch
 		currentBatch.RetryCounter = maxRetryAttempts
-		exError := ExtractorError{
+		return ExtractorError{
 			Batch:     currentBatch,
 			HasLastId: true,
 			Msg:       fmt.Sprintf("Couldn't cast last id value as int: %s", previousError.Error()),
 		}
-		return exError
 
 	}
 
-	exError := ExtractorError{
+	return ExtractorError{
 		Batch:     *batch,
 		HasLastId: true,
 		LastId:    lastId,
 		Msg:       previousError.Error(),
 	}
-	return exError
 }

cmd/go_migrate/loader-error-handler.go

@@ -0,0 +1,61 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+type LoaderError struct {
+	Chunk
+	Msg string
+}
+
+func (e *LoaderError) Error() string {
+	return e.Msg
+}
+
+func loaderErrorHandler(
+	ctx context.Context,
+	chErrorsIn <-chan LoaderError,
+	chChunksOut chan<- Chunk,
+	chJobErrorsOut chan<- JobError,
+) {
+	for {
+		if ctx.Err() != nil {
+			return
+		}
+
+		select {
+		case <-ctx.Done():
+			return
+
+		case err, ok := <-chErrorsIn:
+			if !ok {
+				return
+			}
+
+			if err.RetryCounter >= maxRetryAttempts {
+				jobError := JobError{
+					ShouldCancelJob: false,
+					Msg:             fmt.Sprintf("chunk %v reached max retries (%d)", err.Id, maxRetryAttempts),
+					Prev:            &err,
+				}
+
+				select {
+				case chJobErrorsOut <- jobError:
+				case <-ctx.Done():
+					return
+				}
+				continue
+			}
+
+			err.RetryCounter++
+
+			select {
+			case chChunksOut <- err.Chunk:
+			case <-ctx.Done():
+				return
+			}
+		}
+	}
+}

cmd/go_migrate/loader.go

@@ -12,18 +12,48 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
-func loadRowsPostgres(ctx context.Context, job MigrationJob, columns []ColumnType, db *pgxpool.Pool, chChunksIn <-chan Chunk) error {
+func loadRowsPostgres(
-	chunkCount := 0
+	ctx context.Context,
-	totalRowsLoaded := 0
+	db *pgxpool.Pool,
-
+	job MigrationJob,
-	for chunk := range chChunksIn {
+	columns []ColumnType,
-		chunkStartTime := time.Now()
+	chChunksIn <-chan Chunk,
-		identifier := pgx.Identifier{job.Schema, job.Table}
+	chErrorsOut chan<- LoaderError,
+) {
+	tableId := pgx.Identifier{job.Schema, job.Table}
 	colNames := Map(columns, func(col ColumnType) string {
 		return col.name
 	})
 
-		copyStartTime := time.Now()
+	for {
+		if ctx.Err() != nil {
+			return
+		}
+
+		select {
+		case <-ctx.Done():
+			return
+		case chunk, ok := <-chChunksIn:
+			if !ok {
+				return
+			}
+
+			if abort := loadChunkPostgres(ctx, db, tableId, colNames, chunk, chErrorsOut); abort {
+				return
+			}
+		}
+	}
+}
+
+func loadChunkPostgres(
+	ctx context.Context,
+	db *pgxpool.Pool,
+	identifier pgx.Identifier,
+	colNames []string,
+	chunk Chunk,
+	chErrorsOut chan<- LoaderError,
+) (abort bool) {
+	chunkStartTime := time.Now()
 	_, err := db.CopyFrom(
 		ctx,
 		identifier,
@@ -32,19 +62,20 @@ func loadRowsPostgres(ctx context.Context, job MigrationJob, columns []ColumnTyp
 	)
 
 	if err != nil {
-			return err
+		select {
+		case chErrorsOut <- LoaderError{Chunk: chunk, Msg: err.Error()}:
+		case <-ctx.Done():
+			return true
+		}
+		return false
 	}
 
-		chunkCount++
-		totalRowsLoaded += len(chunk.Data)
-		copyDuration := time.Since(copyStartTime)
 	chunkDuration := time.Since(chunkStartTime)
 	rowsPerSec := float64(len(chunk.Data)) / chunkDuration.Seconds()
 
-		log.Infof("Loaded chunk #%d: %d rows in %v (copy: %v, %.0f rows/sec) - Total: %d rows", chunkCount, len(chunk.Data), chunkDuration, copyDuration, rowsPerSec, totalRowsLoaded)
+	log.Infof("Loaded chunk: %d rows in %v (%.0f rows/sec)", len(chunk.Data), chunkDuration, rowsPerSec)
-	}
 
-	return nil
+	return false
 }
 
 func loadRowsMssql(ctx context.Context, job MigrationJob, columns []ColumnType, db *sql.DB, in <-chan []UnknownRowValues) error {

cmd/go_migrate/process.go

@@ -50,7 +50,7 @@ func processMigrationJob(sourceDb *sql.DB, targetDb *pgxpool.Pool, job Migration
 		extractorErrorHandler(ctx, chExtractorErrors, chBatches, chJobErrors)
 	}()
 
-	chChunks := make(chan Chunk, QueueSize)
+	chChunksRaw := make(chan Chunk, QueueSize)
 	maxExtractors := min(NumExtractors, len(batches))
 	var wgMssqlExtractors sync.WaitGroup
 
@@ -58,7 +58,7 @@ func processMigrationJob(sourceDb *sql.DB, targetDb *pgxpool.Pool, job Migration
 	extractStartTime := time.Now()
 	for range maxExtractors {
 		wgMssqlExtractors.Go(func() {
-			extractFromMssql(ctx, sourceDb, job, sourceColTypes, ChunkSize, chBatches, chChunks, chExtractorErrors, chJobErrors)
+			extractFromMssql(ctx, sourceDb, job, sourceColTypes, ChunkSize, chBatches, chChunksRaw, chExtractorErrors, chJobErrors)
 		})
 	}
 
@@ -72,41 +72,45 @@ func processMigrationJob(sourceDb *sql.DB, targetDb *pgxpool.Pool, job Migration
 
 	go func() {
 		wgMssqlExtractors.Wait()
-		close(chChunks)
+		close(chChunksRaw)
 		log.Infof("Extraction completed in %v", time.Since(extractStartTime))
 	}()
 
-	chChunksTransform := make(chan Chunk, QueueSize)
+	chChunksTransformed := make(chan Chunk, QueueSize)
 	var wgMssqlTransformers sync.WaitGroup
 
 	log.Infof("Starting %d MSSQL transformers...", maxExtractors)
 	transformStartTime := time.Now()
 	for range maxExtractors {
 		wgMssqlTransformers.Go(func() {
-			transformRowsMssql(ctx, sourceColTypes, chChunks, chChunksTransform, chJobErrors)
+			transformRowsMssql(ctx, sourceColTypes, chChunksRaw, chChunksTransformed, chJobErrors)
 		})
 	}
 
 	go func() {
 		wgMssqlTransformers.Wait()
-		close(chChunksTransform)
+		close(chChunksTransformed)
 		log.Infof("Transformation completed in %v", time.Since(transformStartTime))
 	}()
 
 	var wgPostgresLoaders sync.WaitGroup
+	chLoadersErrors := make(chan LoaderError)
+
+	go func() {
+		loaderErrorHandler(ctx, chLoadersErrors, chChunksTransformed, chJobErrors)
+	}()
 
 	log.Infof("Starting %d PostgreSQL loader(s)...", NumLoaders)
 	loaderStartTime := time.Now()
 
 	for range NumLoaders {
 		wgPostgresLoaders.Go(func() {
-			if err := loadRowsPostgres(ctx, job, targetColTypes, targetDb, chChunksTransform); err != nil {
+			loadRowsPostgres(ctx, targetDb, job, targetColTypes, chChunksTransformed, chLoadersErrors)
-				log.Error("Unexpected error loading data into postgres: ", err)
-			}
 		})
 	}
 
 	wgPostgresLoaders.Wait()
+	close(chLoadersErrors)
 	log.Infof("Loading completed in %v", time.Since(loaderStartTime))
 
 	totalDuration := time.Since(jobStartTime)