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Add checkpoint seq no verification.

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This commit is contained in:
Ben Johnson
2020-12-23 11:15:10 -07:00
parent 311f47fe98
commit 5218a1f2c2
2 changed files with 26 additions and 7 deletions
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29
db.go
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@@ -402,7 +402,7 @@ func (db *DB) Sync() (err error) {
// position of the real WAL hasn't been overwritten by another process.
//
// If we are unable to verify the WAL state then we start a new generation.
info, err := db.verifyWAL()
info, err := db.verify()
if err != nil {
return fmt.Errorf("cannot verify wal state: %w", err)
} else if info.reason != "" {
@@ -461,10 +461,10 @@ func (db *DB) ensureWALExists() (err error) {
return err
}
// verifyWAL ensures the current shadow WAL state matches where it left off from
// verify ensures the current shadow WAL state matches where it left off from
// the real WAL. Returns generation & WAL sync information. If info.reason is
// not blank, verification failed and a new generation should be started.
func (db *DB) verifyWAL() (info syncInfo, err error) {
func (db *DB) verify() (info syncInfo, err error) {
// Look up existing generation.
generation, err := db.CurrentGeneration()
if err != nil {
@@ -498,7 +498,14 @@ func (db *DB) verifyWAL() (info syncInfo, err error) {
}
info.shadowWALSize = fi.Size()
// TODO: Truncate shadow WAL if there is a partial page.
// Truncate shadow WAL if there is a partial page.
// Exit if shadow WAL does not contain a full header.
frameSize := int64(db.pageSize) + WALFrameHeaderSize
if info.shadowWALSize < WALHeaderSize {
return info, fmt.Errorf("short shadow wal: %s", info.shadowWALPath)
} else if (info.shadowWALSize-WALHeaderSize)%frameSize != 0 {
info.shadowWALSize = ((info.shadowWALSize - WALHeaderSize) / frameSize) + WALHeaderSize
}
// If shadow WAL is larger than real WAL then the WAL has been truncated
// so we cannot determine our last state.
@@ -507,16 +514,24 @@ func (db *DB) verifyWAL() (info syncInfo, err error) {
return info, nil
}
// Compare WAL headers. If mismatched then the real WAL has been restarted.
// We'll need to start a new shadow WAL during the sync.
// Compare WAL headers. Ensure that checkpoint sequences match and the
// header is the same or that we have moved to the next sequence. If we have
// out-of-order or skipped checkpoint sequences then we should start a new
// generation.
if hdr0, err := readWALHeader(db.WALPath()); err != nil {
return info, fmt.Errorf("cannot read wal header: %w", err)
} else if hdr1, err := readWALHeader(info.shadowWALPath); err != nil {
return info, fmt.Errorf("cannot read shadow wal header: %w", err)
} else {
} else if seq0, seq1 := readCheckpointSeqNo(hdr0), readCheckpointSeqNo(hdr1); seq0 == seq1 && !bytes.Equal(hdr0, hdr1) {
return info, fmt.Errorf("wal header mismatch: chkpt=%d", seq0)
} else if seq0+1 == seq1 {
info.restart = !bytes.Equal(hdr0, hdr1)
} else if seq0 != seq1 {
return info, fmt.Errorf("non-contiguous checkpoint sequence: real=%d shadow=%d", seq0, seq1)
}
// TODO: Handle checkpoint sequence number rollover.
// Verify last page synced still matches.
if info.shadowWALSize > WALHeaderSize {
offset := info.shadowWALSize - int64(db.pageSize+WALFrameHeaderSize)