fix comments

Author: D3Hunter

Makefile

@@ -530,7 +530,7 @@ br_bins:
 
 .PHONY: data_parsers
 data_parsers: tools/bin/vfsgendev pkg/lightning/mydump/parser_generated.go lightning_web
-	PATH="$(GOPATH)/bin":"$(PATH)":"$(TOOLS)" protoc -I. -I"$(GOPATH)/pkg/mod" pkg/lightning/checkpoints/checkpointspb/file_checkpoints.proto --gogofaster_out=.
+	PATH="$(GOPATH)/bin":"$(PATH)":"$(TOOLS)" protoc -I. -I"$(GOMODCACHE)" pkg/lightning/checkpoints/checkpointspb/file_checkpoints.proto --gogofaster_out=.
 	tools/bin/vfsgendev -source='"github.com/pingcap/tidb/lightning/pkg/web".Res' && mv res_vfsdata.go lightning/pkg/web/
 
 .PHONY: build_dumpling

Makefile.common

@@ -14,6 +14,7 @@
 
 PROJECT=tidb
 GOPATH ?= $(shell go env GOPATH)
+GOMODCACHE ?= $(shell go env GOMODCACHE)
 P=8
 
 # Ensure GOPATH is set before running build process.
@@ -132,4 +133,4 @@ ifneq ("$(CI)", "")
 endif
 BAZEL_INSTRUMENTATION_FILTER := --instrument_test_targets --instrumentation_filter=//pkg/...,//br/...,//dumpling/...
 
-NOGO_FLAG=true
+NOGO_FLAG=true

lightning/pkg/importer/import.go

@@ -1990,6 +1990,11 @@ type deliverResult struct {
 }
 
 func saveCheckpoint(rc *Controller, t *TableImporter, engineID int32, chunk *checkpoints.ChunkCheckpoint) {
+	// we save the XXXBase every time a chunk is finished.
+	// Note, it's possible some chunk with larger autoID range finished first, so
+	// the saved XXXBase is larger, when chunks with smaller autoID range finished
+	// it might have no effect on the saved XXXBase, but it's OK, we only need
+	// the largest.
 	rc.saveCpCh <- saveCp{
 		tableName: t.tableName,
 		merger: &checkpoints.RebaseCheckpointMerger{