Remove CachingBlockstore

The improvements in the range-export code lead to avoid reading most blocks
twice, as well as to allowing some blocks to be written to disk multiple times.

The cache hit-rate went down from being close to 50% to a maximum of 12% at
the very end.

These numbers do not support the maintenance of the CachingBlockstore, which
increases memory usage and causes in the end a time-penalty on the export (as
proven when testing).

api/types.go

@@ -403,7 +403,6 @@ func (m *MsgUuidMapType) UnmarshalJSON(b []byte) error {
 type ChainExportConfig struct {
 	WriteBufferSize   int
 	NumWorkers        int
-	CacheSize         int
 	IncludeMessages   bool
 	IncludeReceipts   bool
 	IncludeStateRoots bool

chain/store/snapshot.go

@@ -508,8 +508,7 @@ func (cs *ChainStore) ExportRange(
 	w io.Writer,
 	head, tail *types.TipSet,
 	messages, receipts, stateroots bool,
-	workers int,
-	cacheSize int) error {
+	workers int) error {
 
 	h := &car.CarHeader{
 		Roots:   head.Cids(),
@@ -520,11 +519,6 @@ func (cs *ChainStore) ExportRange(
 		return xerrors.Errorf("failed to write car header: %s", err)
 	}
 
-	cacheStore, err := NewCachingBlockstore(cs.UnionStore(), cacheSize)
-	if err != nil {
-		return err
-	}
-
 	start := time.Now()
 	log.Infow("walking snapshot range",
 		"head", head.Key(),
@@ -544,7 +538,7 @@ func (cs *ChainStore) ExportRange(
 		includeReceipts: receipts,
 	}
 
-	pw, err := newWalkScheduler(ctx, cacheStore, cfg, w)
+	pw, err := newWalkScheduler(ctx, cs.UnionStore(), cfg, w)
 	if err != nil {
 		return err
 	}

cli/chain.go

@@ -1182,11 +1182,6 @@ var ChainExportRangeCmd = &cli.Command{
 			Usage: "specify the number of workers",
 			Value: 1,
 		},
-		&cli.IntFlag{
-			Name:  "cache-size",
-			Usage: "specify the size of the cache (in objects) to use while exporting",
-			Value: 100_000,
-		},
 		&cli.IntFlag{
 			Name:  "write-buffer",
 			Usage: "specify write buffer size",
@@ -1243,7 +1238,6 @@ var ChainExportRangeCmd = &cli.Command{
 			if err := api.ChainExportRangeInternal(ctx, head.Key(), tail.Key(), lapi.ChainExportConfig{
 				WriteBufferSize:   cctx.Int("write-buffer"),
 				NumWorkers:        cctx.Int("workers"),
-				CacheSize:         cctx.Int("cache-size"),
 				IncludeMessages:   cctx.Bool("messages"),
 				IncludeReceipts:   cctx.Bool("receipts"),
 				IncludeStateRoots: cctx.Bool("stateroots"),
@@ -1256,7 +1250,6 @@ var ChainExportRangeCmd = &cli.Command{
 		stream, err := api.ChainExportRange(ctx, head.Key(), tail.Key(), lapi.ChainExportConfig{
 			WriteBufferSize:   cctx.Int("write-buffer"),
 			NumWorkers:        cctx.Int("workers"),
-			CacheSize:         cctx.Int("cache-size"),
 			IncludeMessages:   cctx.Bool("messages"),
 			IncludeReceipts:   cctx.Bool("receipts"),
 			IncludeStateRoots: cctx.Bool("stateroots"),

node/impl/full/chain.go

@@ -630,7 +630,7 @@ func (a ChainAPI) ChainExportRangeInternal(ctx context.Context, head, tail types
 		bw,
 		headTs, tailTs,
 		cfg.IncludeMessages, cfg.IncludeReceipts, cfg.IncludeStateRoots,
-		cfg.NumWorkers, cfg.CacheSize,
+		cfg.NumWorkers,
 	); err != nil {
 		return fmt.Errorf("exporting chain range: %w", err)
 	}
@@ -658,7 +658,7 @@ func (a ChainAPI) ChainExportRange(ctx context.Context, head, tail types.TipSetK
 			headTs,
 			tailTs,
 			cfg.IncludeMessages, cfg.IncludeReceipts, cfg.IncludeStateRoots,
-			cfg.NumWorkers, cfg.CacheSize,
+			cfg.NumWorkers,
 		)
 		bw.Flush()            //nolint:errcheck // it is a write to a pipe
 		w.CloseWithError(err) //nolint:errcheck // it is a pipe