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401 lines
8.9 KiB
401 lines
8.9 KiB
// Copyright 2014 The lldb Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Two Phase Commit & Structural ACID
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package lldb // import "modernc.org/lldb"
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import (
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"bufio"
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"encoding/binary"
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"fmt"
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"io"
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"os"
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"modernc.org/fileutil"
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"modernc.org/mathutil"
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)
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var _ Filer = &ACIDFiler0{} // Ensure ACIDFiler0 is a Filer
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type acidWrite struct {
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b []byte
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off int64
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}
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type acidWriter0 ACIDFiler0
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func (a *acidWriter0) WriteAt(b []byte, off int64) (n int, err error) {
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f := (*ACIDFiler0)(a)
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if f.newEpoch {
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f.newEpoch = false
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f.data = f.data[:0]
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if err = a.writePacket([]interface{}{wpt00Header, walTypeACIDFiler0, ""}); err != nil {
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return
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}
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}
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if err = a.writePacket([]interface{}{wpt00WriteData, b, off}); err != nil {
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return
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}
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f.data = append(f.data, acidWrite{b, off})
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return len(b), nil
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}
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func (a *acidWriter0) writePacket(items []interface{}) (err error) {
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f := (*ACIDFiler0)(a)
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b, err := EncodeScalars(items...)
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if err != nil {
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return
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}
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var b4 [4]byte
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binary.BigEndian.PutUint32(b4[:], uint32(len(b)))
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if _, err = f.bwal.Write(b4[:]); err != nil {
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return
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}
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if _, err = f.bwal.Write(b); err != nil {
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return
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}
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if m := (4 + len(b)) % 16; m != 0 {
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var pad [15]byte
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_, err = f.bwal.Write(pad[:16-m])
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}
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return
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}
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// WAL Packet Tags
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const (
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wpt00Header = iota
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wpt00WriteData
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wpt00Checkpoint
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wpt00Empty
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)
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const (
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walTypeACIDFiler0 = iota
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)
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// ACIDFiler0 is a very simple, synchronous implementation of 2PC. It uses a
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// single write ahead log file to provide the structural atomicity
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// (BeginUpdate/EndUpdate/Rollback) and durability (DB can be recovered from
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// WAL if a crash occurred).
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//
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// ACIDFiler0 is a Filer.
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//
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// NOTE: Durable synchronous 2PC involves three fsyncs in this implementation
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// (WAL, DB, zero truncated WAL). Where possible, it's recommended to collect
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// transactions for, say one second before performing the two phase commit as
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// the typical performance for rotational hard disks is about few tens of
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// fsyncs per second atmost. For an example of such collective transaction
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// approach please see the colecting FSM STT in Dbm's documentation[1].
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//
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// [1]: http://godoc.org/modernc.org/exp/dbm
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type ACIDFiler0 struct {
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*RollbackFiler
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bwal *bufio.Writer
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data []acidWrite
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newEpoch bool
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peakWal int64 // tracks WAL maximum used size
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testHook bool // keeps WAL untruncated (once)
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wal *os.File
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walOptions walOptions
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}
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type walOptions struct {
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headroom int64 // Minimum WAL size.
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}
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// WALOption amends WAL properties.
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type WALOption func(*walOptions) error
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// MinWAL sets the minimum size a WAL file will have. The "extra" allocated
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// file space serves as a headroom. Commits that fit into the headroom should
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// not fail due to 'not enough space on the volume' errors.
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//
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// The min parameter is first rounded-up to a non negative multiple of the size
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// of the Allocator atom.
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//
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// Note: Setting minimum WAL size may render the DB non-recoverable when a
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// crash occurs and the DB is opened in an earlier version of LLDB that does
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// not support minimum WAL sizes.
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func MinWAL(min int64) WALOption {
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min = mathutil.MaxInt64(0, min)
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if r := min % 16; r != 0 {
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min += 16 - r
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}
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return func(o *walOptions) error {
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o.headroom = min
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return nil
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}
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}
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// NewACIDFiler0 returns a newly created ACIDFiler0 with WAL in wal.
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//
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// If the WAL is zero sized then a previous clean shutdown of db is taken for
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// granted and no recovery procedure is taken.
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//
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// If the WAL is of non zero size then it is checked for having a
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// committed/fully finished transaction not yet been reflected in db. If such
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// transaction exists it's committed to db. If the recovery process finishes
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// successfully, the WAL is truncated to the minimum WAL size and fsync'ed
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// prior to return from NewACIDFiler0.
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//
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// opts allow to amend WAL properties.
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func NewACIDFiler(db Filer, wal *os.File, opts ...WALOption) (r *ACIDFiler0, err error) {
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fi, err := wal.Stat()
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if err != nil {
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return
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}
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r = &ACIDFiler0{wal: wal}
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for _, o := range opts {
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if err := o(&r.walOptions); err != nil {
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return nil, err
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}
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}
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if fi.Size() != 0 {
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if err = r.recoverDb(db); err != nil {
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return
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}
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}
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r.bwal = bufio.NewWriter(r.wal)
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r.newEpoch = true
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acidWriter := (*acidWriter0)(r)
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if r.RollbackFiler, err = NewRollbackFiler(
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db,
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func(sz int64) (err error) {
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// Checkpoint
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if err = acidWriter.writePacket([]interface{}{wpt00Checkpoint, sz}); err != nil {
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return
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}
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if err = r.bwal.Flush(); err != nil {
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return
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}
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if err = r.wal.Sync(); err != nil {
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return
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}
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var wfi os.FileInfo
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if wfi, err = r.wal.Stat(); err != nil {
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return
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}
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r.peakWal = mathutil.MaxInt64(wfi.Size(), r.peakWal)
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// Phase 1 commit complete
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for _, v := range r.data {
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n := len(v.b)
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if m := v.off + int64(n); m > sz {
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if n -= int(m - sz); n <= 0 {
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continue
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}
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}
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if _, err = db.WriteAt(v.b[:n], v.off); err != nil {
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return err
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}
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}
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if err = db.Truncate(sz); err != nil {
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return
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}
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if err = db.Sync(); err != nil {
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return
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}
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// Phase 2 commit complete
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if !r.testHook {
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if err := r.emptyWAL(); err != nil {
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return err
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}
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}
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r.testHook = false
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r.bwal.Reset(r.wal)
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r.newEpoch = true
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return r.wal.Sync()
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},
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acidWriter,
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); err != nil {
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return
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}
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return r, nil
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}
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func (a *ACIDFiler0) emptyWAL() error {
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if err := a.wal.Truncate(a.walOptions.headroom); err != nil {
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return err
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}
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if _, err := a.wal.Seek(0, 0); err != nil {
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return err
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}
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if a.walOptions.headroom != 0 {
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a.bwal.Reset(a.wal)
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if err := (*acidWriter0)(a).writePacket([]interface{}{wpt00Empty}); err != nil {
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return err
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}
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if err := a.bwal.Flush(); err != nil {
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return err
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}
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if _, err := a.wal.Seek(0, 0); err != nil {
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return err
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}
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}
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return nil
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}
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// PeakWALSize reports the maximum size WAL has ever used.
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func (a ACIDFiler0) PeakWALSize() int64 {
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return a.peakWal
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}
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func (a *ACIDFiler0) readPacket(f *bufio.Reader) (items []interface{}, err error) {
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var b4 [4]byte
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n, err := io.ReadAtLeast(f, b4[:], 4)
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if n != 4 {
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return
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}
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ln := int(binary.BigEndian.Uint32(b4[:]))
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m := (4 + ln) % 16
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padd := (16 - m) % 16
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b := make([]byte, ln+padd)
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if n, err = io.ReadAtLeast(f, b, len(b)); n != len(b) {
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return
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}
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return DecodeScalars(b[:ln])
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}
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func (a *ACIDFiler0) recoverDb(db Filer) (err error) {
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fi, err := a.wal.Stat()
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if err != nil {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: err}
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}
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if sz := fi.Size(); sz%16 != 0 {
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return &ErrILSEQ{Type: ErrFileSize, Name: a.wal.Name(), Arg: sz}
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}
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f := bufio.NewReader(a.wal)
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items, err := a.readPacket(f)
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if err != nil {
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return
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}
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if items[0] == int64(wpt00Empty) {
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if len(items) != 1 {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("invalid packet items %#v", items)}
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}
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return nil
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}
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if len(items) != 3 || items[0] != int64(wpt00Header) || items[1] != int64(walTypeACIDFiler0) {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("invalid packet items %#v", items)}
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}
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tr := NewBTree(nil)
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for {
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items, err = a.readPacket(f)
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if err != nil {
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return
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}
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if len(items) < 2 {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("too few packet items %#v", items)}
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}
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switch items[0] {
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case int64(wpt00WriteData):
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if len(items) != 3 {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("invalid data packet items %#v", items)}
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}
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b, off := items[1].([]byte), items[2].(int64)
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var key [8]byte
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binary.BigEndian.PutUint64(key[:], uint64(off))
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if err = tr.Set(key[:], b); err != nil {
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return
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}
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case int64(wpt00Checkpoint):
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var b1 [1]byte
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if n, err := f.Read(b1[:]); n != 0 || err == nil {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("checkpoint n %d, err %v", n, err)}
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}
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if len(items) != 2 {
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("checkpoint packet invalid items %#v", items)}
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}
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sz := items[1].(int64)
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enum, err := tr.seekFirst()
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if err != nil {
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return err
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}
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for {
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var k, v []byte
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k, v, err = enum.current()
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if err != nil {
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if fileutil.IsEOF(err) {
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break
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}
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return err
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}
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if _, err = db.WriteAt(v, int64(binary.BigEndian.Uint64(k))); err != nil {
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return err
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}
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if err = enum.next(); err != nil {
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if fileutil.IsEOF(err) {
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break
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}
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return err
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}
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}
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if err = db.Truncate(sz); err != nil {
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return err
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}
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if err = db.Sync(); err != nil {
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return err
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}
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// Recovery complete
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if err := a.emptyWAL(); err != nil {
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return err
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}
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return a.wal.Sync()
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default:
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return &ErrILSEQ{Type: ErrInvalidWAL, Name: a.wal.Name(), More: fmt.Sprintf("packet tag %v", items[0])}
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}
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}
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}
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