diff --git a/br/pkg/lightning/mydump/region.go b/br/pkg/lightning/mydump/region.go
index d5d5b06f9ded4..796a09a38a3f3 100644
--- a/br/pkg/lightning/mydump/region.go
+++ b/br/pkg/lightning/mydump/region.go
@@ -35,6 +35,7 @@ const (
 	// the increment ratio of large CSV file size threshold by `region-split-size`
 	largeCSVLowerThresholdRation = 10
 	// TableFileSizeINF for compressed size, for lightning 10TB is a relatively big value and will strongly affect efficiency
+	// It's used to make sure compressed files can be read until EOF. Because we can't get the exact decompressed size of the compressed files.
 	TableFileSizeINF = 10 * 1024 * tableRegionSizeWarningThreshold
 )
 
@@ -300,7 +301,7 @@ func MakeSourceFileRegion(
 	// set fileSize to INF to make sure compressed files can be read until EOF. Because we can't get the exact size of the compressed files.
 	// TODO: update progress bar calculation for compressed files.
 	if fi.FileMeta.Compression != CompressionNone {
-		rowIDMax = fileSize * 100 / divisor
+		rowIDMax = fileSize * 100 / divisor // FIXME: this is not accurate. Need more tests and fix solution.
 		fileSize = TableFileSizeINF
 	}
 	tableRegion := &TableRegion{