feat: implement batch processing for MSSQL extraction and transformation with range handling

cmd/go_migrate/build-extract-query.go

@@ -5,30 +5,36 @@ import (
 	"strings"
 )
 
-func buildExtractQueryMssql(job MigrationJob, columns []ColumnType) string {
-	var sbColumns strings.Builder
+func buildExtractQueryMssql(job MigrationJob, columns []ColumnType, includeRange bool) string {
+	var sbQuery strings.Builder
+
+	sbQuery.WriteString("SELECT ")
 
 	if len(columns) == 0 {
-		sbColumns.WriteString("*")
+		sbQuery.WriteString("*")
 	} else {
 		for i, col := range columns {
-			sbColumns.WriteString("[")
-			sbColumns.WriteString(col.name)
-			sbColumns.WriteString("]")
+			fmt.Fprintf(&sbQuery, "[%s]", col.name)
 
 			if col.unifiedType == "GEOMETRY" {
-				sbColumns.WriteString(".STAsBinary() AS [")
-				sbColumns.WriteString(col.name)
-				sbColumns.WriteString("]")
+				fmt.Fprintf(&sbQuery, ".STAsBinary() AS [%s]", col.name)
 			}
 
 			if i < len(columns)-1 {
-				sbColumns.WriteString(", ")
+				sbQuery.WriteString(", ")
 			}
 		}
 	}
 
-	return fmt.Sprintf(`SELECT %s FROM [%s].[%s] ORDER BY [%s] ASC`, sbColumns.String(), job.Schema, job.Table, job.PrimaryKey)
+	fmt.Fprintf(&sbQuery, " FROM [%s].[%s]", job.Schema, job.Table)
+
+	if includeRange {
+		fmt.Fprintf(&sbQuery, " WHERE [%s] BETWEEN @minRange AND @maxRange", job.PrimaryKey)
+	}
+
+	fmt.Fprintf(&sbQuery, " ORDER BY [%s] ASC", job.PrimaryKey)
+
+	return sbQuery.String()
 }
 
 func buildExtractQueryPostgres(job MigrationJob, columns []ColumnType) string {

cmd/go_migrate/chunk-planner.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+type BatchRange struct {
+	LowerLimit int
+	UpperLimit int
+	validRange bool
+}
+
+func estimateTotalRowsMssql(ctx context.Context, db *sql.DB, job MigrationJob) (int, error) {
+	query := `
+SELECT
+	SUM(p.rows) AS count
+FROM sys.tables t
+JOIN sys.schemas s ON t.schema_id = s.schema_id
+JOIN sys.partitions p ON t.object_id = p.object_id
+WHERE s.name = @schema AND t.name = @table AND p.index_id IN (0, 1)
+GROUP BY t.name`
+
+	var rowsCount int
+	err := db.QueryRowContext(ctx, query, sql.Named("schema", job.Schema), sql.Named("table", job.Table)).Scan(&rowsCount)
+	if err != nil {
+		return 0, err
+	}
+
+	return rowsCount, nil
+}
+
+func calculateChunkRangesMssql(ctx context.Context, db *sql.DB, job MigrationJob, batchCount int) ([]BatchRange, error) {
+	query := fmt.Sprintf(`
+SELECT
+	MIN([%s]) AS lower_limit,
+	MAX([%s]) AS upper_limit
+FROM
+	(SELECT [%s], NTILE(@batchCount) OVER (ORDER BY [%s]) AS chunk_id FROM [%s].[%s]) AS T
+GROUP BY chunk_id
+ORDER BY chunk_id`, job.PrimaryKey, job.PrimaryKey, job.PrimaryKey, job.PrimaryKey, job.Schema, job.Table)
+
+	rows, err := db.QueryContext(ctx, query, sql.Named("batchCount", batchCount))
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	batchRanges := make([]BatchRange, 0, batchCount)
+
+	for rows.Next() {
+		var br BatchRange
+		br.validRange = true
+
+		if err := rows.Scan(&br.LowerLimit, &br.UpperLimit); err != nil {
+			return nil, err
+		}
+
+		batchRanges = append(batchRanges, br)
+	}
+
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+
+	return batchRanges, nil
+}
+
+const estimatedRowsPerBatch = 100_000
+
+func calculateBatchMetrics(ctx context.Context, db *sql.DB, job MigrationJob) ([]BatchRange, error) {
+	rowsCount, err := estimateTotalRowsMssql(ctx, db, job)
+	if err != nil {
+		return nil, err
+	}
+
+	batchCount := 1
+	if rowsCount > estimatedRowsPerBatch {
+		batchCount = rowsCount / estimatedRowsPerBatch
+	} else {
+		return []BatchRange{{validRange: false}}, nil
+	}
+
+	chunksRange, err := calculateChunkRangesMssql(ctx, db, job, batchCount)
+	if err != nil {
+		return nil, err
+	}
+
+	return chunksRange, nil
+}

cmd/go_migrate/extractor.go

@@ -12,12 +12,20 @@ import (
 
 type UnknownRowValues = []any
 
-func extractFromMssql(ctx context.Context, job MigrationJob, columns []ColumnType, chunkSize int, db *sql.DB, out chan<- []UnknownRowValues) error {
-	query := buildExtractQueryMssql(job, columns)
+func extractFromMssql(ctx context.Context, db *sql.DB, job MigrationJob, columns []ColumnType, chunkSize int, batchRange BatchRange, out chan<- []UnknownRowValues) error {
+	query := buildExtractQueryMssql(job, columns, batchRange.validRange)
 	log.Debug("Query used to extract data from mssql: ", query)
 
+	var queryArgs []any
+	if batchRange.validRange {
+		queryArgs = append(queryArgs,
+			sql.Named("minRange", batchRange.LowerLimit),
+			sql.Named("maxRange", batchRange.UpperLimit),
+		)
+	}
+
 	queryStartTime := time.Now()
-	rows, err := db.QueryContext(ctx, query)
+	rows, err := db.QueryContext(ctx, query, queryArgs...)
 	if err != nil {
 		return err
 	}

cmd/go_migrate/main.go

@@ -21,10 +21,10 @@ var migrationJobs []MigrationJob = []MigrationJob{
 }
 
 const (
-	NumExtractors int = 1
-	NumLoaders    int = 4
-	ChunkSize     int = 50000
-	QueueSize     int = 10
+	NumExtractors   int = 4
+	NumLoaders      int = 4
+	ChunkSize       int = 50000
+	QueueSize       int = 10
 )
 
 func main() {

cmd/go_migrate/process.go

@@ -24,24 +24,56 @@ func processMigrationJob(sourceDb *sql.DB, targetDb *pgxpool.Pool, job Migration
 	logColumnTypes(sourceColTypes, "Source col types")
 	logColumnTypes(targetColTypes, "Target col types")
 
-	chRowsExtract := make(chan []UnknownRowValues, QueueSize)
-	chRowsTransform := make(chan []UnknownRowValues)
 	mssqlCtx := context.Background()
+	batchRanges, err := calculateBatchMetrics(mssqlCtx, sourceDb, job)
+	if err != nil {
+		log.Error("Unexpected error calculating batch ranges: ", err)
+	}
+
+	chBatchRanges := make(chan BatchRange, len(batchRanges))
+
+	maxExtractors := min(NumExtractors, len(batchRanges))
+	chRowsExtract := make(chan []UnknownRowValues, QueueSize)
+	var wgMssqlExtractors sync.WaitGroup
+
+	log.Infof("Starting %d MSSQL extractors...", maxExtractors)
+	extractStartTime := time.Now()
+	for range maxExtractors {
+		wgMssqlExtractors.Go(func() {
+			for br := range chBatchRanges {
+				if err := extractFromMssql(mssqlCtx, sourceDb, job, sourceColTypes, ChunkSize, br, chRowsExtract); err != nil {
+					log.Error("Unexpected error extracting data from mssql: ", err)
+				}
+			}
+		})
+	}
 
 	go func() {
-		log.Info("Starting extraction from MSSQL...")
-		extractStartTime := time.Now()
-		if err := extractFromMssql(mssqlCtx, job, sourceColTypes, ChunkSize, sourceDb, chRowsExtract); err != nil {
-			log.Error("Unexpected error extracting data from mssql: ", err)
+		for _, br := range batchRanges {
+			chBatchRanges <- br
 		}
+		close(chBatchRanges)
+	}()
+
+	go func() {
+		wgMssqlExtractors.Wait()
 		close(chRowsExtract)
 		log.Infof("Extraction completed in %v", time.Since(extractStartTime))
 	}()
 
+	chRowsTransform := make(chan []UnknownRowValues, QueueSize)
+	var wgMssqlTransformers sync.WaitGroup
+
+	log.Infof("Starting %d MSSQL transformers...", maxExtractors)
+	transformStartTime := time.Now()
+	for range maxExtractors {
+		wgMssqlTransformers.Go(func() {
+			transformRowsMssql(sourceColTypes, chRowsExtract, chRowsTransform)
+		})
+	}
+
 	go func() {
-		log.Info("Starting transformation of rows...")
-		transformStartTime := time.Now()
-		transformRowsMssql(sourceColTypes, chRowsExtract, chRowsTransform)
+		wgMssqlTransformers.Wait()
 		close(chRowsTransform)
 		log.Infof("Transformation completed in %v", time.Since(transformStartTime))
 	}()