core: report progress on log chain exports (#17066)

* core/blockchain: export progress

* core: polish up chain export progress report a bit

cmd/geth/chaincmd.go

@@ -94,7 +94,8 @@ processing will proceed even if an individual RLP-file import failure occurs.`,
 Requires a first argument of the file to write to.
 Optional second and third arguments control the first and
 last block to write. In this mode, the file will be appended
-if already existing.`,
+if already existing. If the file ends with .gz, the output will
+be gzipped.`,
 	}
 	importPreimagesCommand = cli.Command{
 		Action:    utils.MigrateFlags(importPreimages),

core/blockchain.go

@@ -450,15 +450,19 @@ func (bc *BlockChain) ExportN(w io.Writer, first uint64, last uint64) error {
 	}
 	log.Info("Exporting batch of blocks", "count", last-first+1)
 
+	start, reported := time.Now(), time.Now()
 	for nr := first; nr <= last; nr++ {
 		block := bc.GetBlockByNumber(nr)
 		if block == nil {
 			return fmt.Errorf("export failed on #%d: not found", nr)
 		}
-
 		if err := block.EncodeRLP(w); err != nil {
 			return err
 		}
+		if time.Since(reported) >= statsReportLimit {
+			log.Info("Exporting blocks", "exported", block.NumberU64()-first, "elapsed", common.PrettyDuration(time.Since(start)))
+			reported = time.Now()
+		}
 	}
 
 	return nil
@@ -1203,8 +1207,8 @@ type insertStats struct {
 	startTime                  mclock.AbsTime
 }
 
-// statsReportLimit is the time limit during import after which we always print
-// out progress. This avoids the user wondering what's going on.
+// statsReportLimit is the time limit during import and export after which we
+// always print out progress. This avoids the user wondering what's going on.
 const statsReportLimit = 8 * time.Second
 
 // report prints statistics if some number of blocks have been processed