core/rawdb: add logging and fix comments around AncientRange function…

core/rawdb/accessors_chain.go

@@ -351,13 +351,18 @@ func ReadHeaderRange(db ctxcdb.Reader, number uint64, count uint64) []rlp.RawVal
 		return rlpHeaders
 	}
 	// read remaining from ancients
-	max := count * 700
-	data, err := db.AncientRange(ChainFreezerHeaderTable, i+1-count, count, max)
-	if err == nil && uint64(len(data)) == count {
-		// the data is on the order [h, h+1, .., n] -- reordering needed
-		for i := range data {
-			rlpHeaders = append(rlpHeaders, data[len(data)-1-i])
-		}
+	data, err := db.AncientRange(ChainFreezerHeaderTable, i+1-count, count, 0)
+	if err != nil {
+		log.Error("Failed to read headers from freezer", "err", err)
+		return rlpHeaders
+	}
+	if uint64(len(data)) != count {
+		log.Warn("Incomplete read of headers from freezer", "wanted", count, "read", len(data))
+		return rlpHeaders
+	}
+	// The data is on the order [h, h+1, .., n] -- reordering needed
+	for i := range data {
+		rlpHeaders = append(rlpHeaders, data[len(data)-1-i])
 	}
 	return rlpHeaders
 }

core/rawdb/freezer_resettable.go

@@ -119,9 +119,10 @@ func (f *ResettableFreezer) Ancient(kind string, number uint64) ([]byte, error)
 
 // AncientRange retrieves multiple items in sequence, starting from the index 'start'.
 // It will return
-//   - at most 'max' items,
-//   - at least 1 item (even if exceeding the maxByteSize), but will otherwise
-//     return as many items as fit into maxByteSize
+//   - at most 'count' items,
+//   - if maxBytes is specified: at least 1 item (even if exceeding the maxByteSize),
+//     but will otherwise return as many items as fit into maxByteSize.
+//   - if maxBytes is not specified, 'count' items will be returned if they are present.
 func (f *ResettableFreezer) AncientRange(kind string, start, count, maxBytes uint64) ([][]byte, error) {
 	f.lock.RLock()
 	defer f.lock.RUnlock()