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add ReadOnly config option for read-only filesystems #53

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add ReadOnly config option for read-only filesystems #53

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6 changes: 3 additions & 3 deletions datalog.go
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Original file line number Diff line number Diff line change
Expand Up @@ -79,15 +79,15 @@ func parseSegmentName(name string) (uint16, uint64, error) {
}

func (dl *datalog) openSegment(name string, id uint16, seqID uint64) (*segment, error) {
f, err := openFile(dl.opts.FileSystem, name, false)
f, err := openFile(dl.opts.FileSystem, name, false, dl.opts.ReadOnly)
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Wondering if rather than modifying all openFile calls it would be cleaner to implement a new file system wrapper similar to fs.Sub? The wrapper would set os.O_RDONLY flags and implement a noop CreateLockFile.

if err != nil {
return nil, err
}

meta := &segmentMeta{}
if !f.empty() {
metaName := name + metaExt
if err := readGobFile(dl.opts.FileSystem, metaName, &meta); err != nil {
if err := readGobFile(dl.opts.FileSystem, metaName, &meta, dl.opts.ReadOnly); err != nil {
logger.Printf("error reading segment meta %d: %v", id, err)
// TODO: rebuild meta?
}
Expand Down Expand Up @@ -235,7 +235,7 @@ func (dl *datalog) close() error {
return err
}
metaName := seg.name + metaExt
if err := writeGobFile(dl.opts.FileSystem, metaName, seg.meta); err != nil {
if err := writeGobFile(dl.opts.FileSystem, metaName, seg.meta, dl.opts.ReadOnly); err != nil {
return err
}
}
Expand Down
32 changes: 21 additions & 11 deletions db.go
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Original file line number Diff line number Diff line change
Expand Up @@ -56,20 +56,28 @@ func Open(path string, opts *Options) (*DB, error) {
return nil, err
}

// Try to acquire a file lock.
lock, acquiredExistingLock, err := createLockFile(opts)
var lock fs.LockFile
var err error
var acquiredExistingLock bool
if !opts.ReadOnly {
// Try to acquire a file lock.
lock, acquiredExistingLock, err = createLockFile(opts)
}
if err != nil {
if err == os.ErrExist {
err = errLocked
}
return nil, errors.Wrap(err, "creating lock file")
}
clean := lock.Unlock
defer func() {
if clean != nil {
_ = clean()
}
}()
var clean func() error
if !opts.ReadOnly {
clean = lock.Unlock
defer func() {
if clean != nil {
_ = clean()
}
}()
}

if acquiredExistingLock {
// Lock file already existed, but the process managed to acquire it.
Expand Down Expand Up @@ -121,7 +129,9 @@ func Open(path string, opts *Options) (*DB, error) {
db.startBackgroundWorker()
}

clean = nil
if !opts.ReadOnly {
clean = nil
}
return db, nil
}

Expand All @@ -135,12 +145,12 @@ func (db *DB) writeMeta() error {
m := dbMeta{
HashSeed: db.hashSeed,
}
return writeGobFile(db.opts.FileSystem, dbMetaName, m)
return writeGobFile(db.opts.FileSystem, dbMetaName, m, db.opts.ReadOnly)
}

func (db *DB) readMeta() error {
m := dbMeta{}
if err := readGobFile(db.opts.FileSystem, dbMetaName, &m); err != nil {
if err := readGobFile(db.opts.FileSystem, dbMetaName, &m, db.opts.ReadOnly); err != nil {
return err
}
db.hashSeed = m.HashSeed
Expand Down
11 changes: 7 additions & 4 deletions file.go
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Original file line number Diff line number Diff line change
Expand Up @@ -14,10 +14,13 @@ type file struct {
size int64
}

func openFile(fsyst fs.FileSystem, name string, truncate bool) (*file, error) {
flag := os.O_CREATE | os.O_RDWR
if truncate {
flag |= os.O_TRUNC
func openFile(fsyst fs.FileSystem, name string, truncate bool, readOnly bool) (*file, error) {
var flag int = os.O_RDONLY
if !readOnly {
flag = os.O_CREATE | os.O_RDWR
if truncate {
flag |= os.O_TRUNC
}
}
fi, err := fsyst.OpenFile(name, flag, os.FileMode(0640))
f := &file{}
Expand Down
8 changes: 4 additions & 4 deletions gobfile.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,8 @@ import (
"github.com/akrylysov/pogreb/fs"
)

func readGobFile(fsys fs.FileSystem, name string, v interface{}) error {
f, err := openFile(fsys, name, false)
func readGobFile(fsys fs.FileSystem, name string, v interface{}, readOnly bool) error {
f, err := openFile(fsys, name, false, readOnly)
if err != nil {
return err
}
Expand All @@ -16,8 +16,8 @@ func readGobFile(fsys fs.FileSystem, name string, v interface{}) error {
return dec.Decode(v)
}

func writeGobFile(fsys fs.FileSystem, name string, v interface{}) error {
f, err := openFile(fsys, name, true)
func writeGobFile(fsys fs.FileSystem, name string, v interface{}, readOnly bool) error {
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What would be the desired effect of writing to a file opened in read-only mode? Wouldn't it always fail?

f, err := openFile(fsys, name, true, readOnly)
if err != nil {
return err
}
Expand Down
8 changes: 4 additions & 4 deletions index.go
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Original file line number Diff line number Diff line change
Expand Up @@ -38,11 +38,11 @@ type indexMeta struct {
type matchKeyFunc func(slot) (bool, error)

func openIndex(opts *Options) (*index, error) {
main, err := openFile(opts.FileSystem, indexMainName, false)
main, err := openFile(opts.FileSystem, indexMainName, false, opts.ReadOnly)
if err != nil {
return nil, errors.Wrap(err, "opening main index")
}
overflow, err := openFile(opts.FileSystem, indexOverflowName, false)
overflow, err := openFile(opts.FileSystem, indexOverflowName, false, opts.ReadOnly)
if err != nil {
_ = main.Close()
return nil, errors.Wrap(err, "opening overflow index")
Expand Down Expand Up @@ -76,12 +76,12 @@ func (idx *index) writeMeta() error {
SplitBucketIndex: idx.splitBucketIdx,
FreeOverflowBuckets: idx.freeBucketOffs,
}
return writeGobFile(idx.opts.FileSystem, indexMetaName, m)
return writeGobFile(idx.opts.FileSystem, indexMetaName, m, idx.opts.ReadOnly)
}

func (idx *index) readMeta() error {
m := indexMeta{}
if err := readGobFile(idx.opts.FileSystem, indexMetaName, &m); err != nil {
if err := readGobFile(idx.opts.FileSystem, indexMetaName, &m, idx.opts.ReadOnly); err != nil {
return err
}
idx.level = m.Level
Expand Down
3 changes: 3 additions & 0 deletions options.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,9 @@ type Options struct {
// Default: fs.OSMMap.
FileSystem fs.FileSystem

// Does DB reside on read-only filesystem?
ReadOnly bool

maxSegmentSize uint32
compactionMinSegmentSize uint32
compactionMinFragmentation float32
Expand Down