1 // Copyright (c) 2015-2016 The btcsuite developers
2 // Use of this source code is governed by an ISC
3 // license that can be found in the LICENSE file.
11 "github.com/btcsuite/btcd/database"
14 // The serialized write cursor location format is:
16 // [0:4] Block file (4 bytes)
17 // [4:8] File offset (4 bytes)
18 // [8:12] Castagnoli CRC-32 checksum (4 bytes)
20 // serializeWriteRow serialize the current block file and offset where new
21 // will be written into a format suitable for storage into the metadata.
22 func serializeWriteRow(curBlockFileNum, curFileOffset uint32) []byte {
23 var serializedRow [12]byte
24 byteOrder.PutUint32(serializedRow[0:4], curBlockFileNum)
25 byteOrder.PutUint32(serializedRow[4:8], curFileOffset)
26 checksum := crc32.Checksum(serializedRow[:8], castagnoli)
27 byteOrder.PutUint32(serializedRow[8:12], checksum)
28 return serializedRow[:]
31 // deserializeWriteRow deserializes the write cursor location stored in the
32 // metadata. Returns ErrCorruption if the checksum of the entry doesn't match.
33 func deserializeWriteRow(writeRow []byte) (uint32, uint32, error) {
34 // Ensure the checksum matches. The checksum is at the end.
35 gotChecksum := crc32.Checksum(writeRow[:8], castagnoli)
36 wantChecksumBytes := writeRow[8:12]
37 wantChecksum := byteOrder.Uint32(wantChecksumBytes)
38 if gotChecksum != wantChecksum {
39 str := fmt.Sprintf("metadata for write cursor does not match "+
40 "the expected checksum - got %d, want %d", gotChecksum,
42 return 0, 0, makeDbErr(database.ErrCorruption, str, nil)
45 fileNum := byteOrder.Uint32(writeRow[0:4])
46 fileOffset := byteOrder.Uint32(writeRow[4:8])
47 return fileNum, fileOffset, nil
50 // reconcileDB reconciles the metadata with the flat block files on disk. It
51 // will also initialize the underlying database if the create flag is set.
52 func reconcileDB(pdb *db, create bool) (database.DB, error) {
53 // Perform initial internal bucket and value creation during database
56 if err := initDB(pdb.cache.ldb); err != nil {
61 // Load the current write cursor position from the metadata.
62 var curFileNum, curOffset uint32
63 err := pdb.View(func(tx database.Tx) error {
64 writeRow := tx.Metadata().Get(writeLocKeyName)
66 str := "write cursor does not exist"
67 return makeDbErr(database.ErrCorruption, str, nil)
71 curFileNum, curOffset, err = deserializeWriteRow(writeRow)
78 // When the write cursor position found by scanning the block files on
79 // disk is AFTER the position the metadata believes to be true, truncate
80 // the files on disk to match the metadata. This can be a fairly common
81 // occurrence in unclean shutdown scenarios while the block files are in
82 // the middle of being written. Since the metadata isn't updated until
83 // after the block data is written, this is effectively just a rollback
84 // to the known good point before the unclean shutdown.
85 wc := pdb.store.writeCursor
86 if wc.curFileNum > curFileNum || (wc.curFileNum == curFileNum &&
87 wc.curOffset > curOffset) {
89 log.Info("Detected unclean shutdown - Repairing...")
90 log.Debugf("Metadata claims file %d, offset %d. Block data is "+
91 "at file %d, offset %d", curFileNum, curOffset,
92 wc.curFileNum, wc.curOffset)
93 pdb.store.handleRollback(curFileNum, curOffset)
94 log.Infof("Database sync complete")
97 // When the write cursor position found by scanning the block files on
98 // disk is BEFORE the position the metadata believes to be true, return
99 // a corruption error. Since sync is called after each block is written
100 // and before the metadata is updated, this should only happen in the
101 // case of missing, deleted, or truncated block files, which generally
102 // is not an easily recoverable scenario. In the future, it might be
103 // possible to rescan and rebuild the metadata from the block files,
104 // however, that would need to happen with coordination from a higher
105 // layer since it could invalidate other metadata.
106 if wc.curFileNum < curFileNum || (wc.curFileNum == curFileNum &&
107 wc.curOffset < curOffset) {
109 str := fmt.Sprintf("metadata claims file %d, offset %d, but "+
110 "block data is at file %d, offset %d", curFileNum,
111 curOffset, wc.curFileNum, wc.curOffset)
112 log.Warnf("***Database corruption detected***: %v", str)
113 return nil, makeDbErr(database.ErrCorruption, str, nil)