refactor: update extractor interfaces to return row counts instead of using pointers for rows read

internal/app/etl/extractors/postgres.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"strings"
 	"sync"
-	"sync/atomic"
 
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
 	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
@@ -60,17 +59,17 @@ func (postgresEx *PostgresExtractor) ProcessPartition(
 	partition models.Partition,
 	indexPrimaryKey int,
 	chBatchesOut chan<- models.Batch,
-	rowsRead *int64,
-) error {
+) (int, error) {
 	query := buildExtractQueryPostgres(tableInfo, columns)
 
 	if partition.ShouldUseRange {
-		return errors.New("Batch config not yet supported")
+		return 0, errors.New("Batch config not yet supported")
 	}
 
+	rowsRead := 0
 	rows, err := postgresEx.db.Query(ctx, query)
 	if err != nil {
-		return &custom_errors.ExtractorError{Partition: partition, HasLastId: false, Msg: err.Error()}
+		return rowsRead, &custom_errors.ExtractorError{Partition: partition, HasLastId: false, Msg: err.Error()}
 	}
 	defer rows.Close()
 
@@ -79,8 +78,9 @@ func (postgresEx *PostgresExtractor) ProcessPartition(
 	for rows.Next() {
 		values, err := rows.Values()
 		if err != nil {
-			return errors.New("Unexpected error reading rows from source")
+			return rowsRead, errors.New("Unexpected error reading rows from source")
 		}
+		rowsRead++
 
 		batchRows = append(batchRows, values)
 
@@ -88,29 +88,26 @@ func (postgresEx *PostgresExtractor) ProcessPartition(
 			select {
 			case chBatchesOut <- models.Batch{Id: uuid.New(), PartitionId: partition.Id, Rows: batchRows, RetryCounter: 0}:
 			case <-ctx.Done():
-				return nil
+				return rowsRead, ctx.Err()
 			}
 
-			atomic.AddInt64(rowsRead, int64(len(batchRows)))
 			batchRows = make([]models.UnknownRowValues, 0, batchSize)
 		}
 	}
 
 	if err := rows.Err(); err != nil {
-		return errors.New("Unexpected error reading rows from source")
+		return rowsRead, errors.New("Unexpected error reading rows from source")
 	}
 
 	if len(batchRows) > 0 {
 		select {
 		case chBatchesOut <- models.Batch{Id: uuid.New(), PartitionId: partition.Id, Rows: batchRows, RetryCounter: 0}:
 		case <-ctx.Done():
-			return nil
+			return rowsRead, nil
 		}
-
-		atomic.AddInt64(rowsRead, int64(len(batchRows)))
 	}
 
-	return nil
+	return rowsRead, nil
 }
 
 func (postgresEx *PostgresExtractor) Exec(