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[#2252] fstree: Allow concurrent writes

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Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
This commit is contained in:
Evgenii Stratonikov 2023-02-09 19:13:51 +03:00 committed by fyrchik
parent b422ac9f94
commit 315141dc2c
1 changed files with 49 additions and 8 deletions
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57
pkg/local_object_storage/blobstor/fstree/fstree.go
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@ -7,6 +7,7 @@ import (
"io/fs" "io/fs"
"os" "os"
"path/filepath" "path/filepath"
"strconv"
"strings" "strings"
"syscall" "syscall"
@ -230,23 +231,63 @@ func (t *FSTree) Put(prm common.PutPrm) (common.PutRes, error) {
prm.RawData = t.Compress(prm.RawData) prm.RawData = t.Compress(prm.RawData)
} }
tmpPath := p + "#" // Here is a situation:
err := t.writeFile(tmpPath, prm.RawData) // Feb 09 13:10:37 buky neofs-node[32445]: 2023-02-09T13:10:37.161Z info log/log.go:13 local object storage operation {"shard_id": "SkT8BfjouW6t93oLuzQ79s", "address": "7NxFz4SruSi8TqXacr2Ae22nekMhgYk1sfkddJo9PpWk/5enyUJGCyU1sfrURDnHEjZFdbGqANVhayYGfdSqtA6wA", "op": "PUT", "type": "fstree", "storage_id": ""}
// Feb 09 13:10:37 buky neofs-node[32445]: 2023-02-09T13:10:37.183Z info log/log.go:13 local object storage operation {"shard_id": "SkT8BfjouW6t93oLuzQ79s", "address": "7NxFz4SruSi8TqXacr2Ae22nekMhgYk1sfkddJo9PpWk/5enyUJGCyU1sfrURDnHEjZFdbGqANVhayYGfdSqtA6wA", "op": "metabase PUT"}
// Feb 09 13:10:37 buky neofs-node[32445]: 2023-02-09T13:10:37.862Z debug policer/check.go:231 shortage of object copies detected {"component": "Object Policer", "object": "7NxFz4SruSi8TqXacr2Ae22nekMhgYk1sfkddJo9PpWk/5enyUJGCyU1sfrURDnHEjZFdbGqANVhayYGfdSqtA6wA", "shortage": 1}
// Feb 09 13:10:37 buky neofs-node[32445]: 2023-02-09T13:10:37.862Z debug shard/get.go:124 object is missing in write-cache {"shard_id": "SkT8BfjouW6t93oLuzQ79s", "addr": "7NxFz4SruSi8TqXacr2Ae22nekMhgYk1sfkddJo9PpWk/5enyUJGCyU1sfrURDnHEjZFdbGqANVhayYGfdSqtA6wA", "skip_meta": false}
//
// 1. We put an object on node 1.
// 2. Relentless policer sees that it has only 1 copy and tries to PUT it to node 2.
// 3. PUT operation started by client at (1) also puts an object here.
// 4. Now we have concurrent writes and one of `Rename` calls will return `no such file` error.
// Even more than that, concurrent writes can corrupt data.
//
// So here is a solution:
// 1. Write a file to 'name + 1'.
// 2. If it exists, retry with temporary name being 'name + 2'.
// 3. Set some reasonable number of attempts.
//
// It is a bit kludgey, but I am unusually proud about having found this out after
// hours of research on linux kernel, dirsync mount option and ext4 FS, turned out
// to be so hecking simple.
// In a very rare situation we can have multiple partially written copies on disk,
// this will be fixed in another issue (we should remove garbage on start).
const retryCount = 5
for i := 0; i < retryCount; i++ {
tmpPath := p + "#" + strconv.FormatUint(uint64(i), 10)
err := t.writeAndRename(tmpPath, p, prm.RawData)
if err != syscall.EEXIST || i == retryCount-1 {
return common.PutRes{StorageID: []byte{}}, err
}
}
// unreachable, but precaution never hurts, especially 1 day before release.
return common.PutRes{StorageID: []byte{}}, fmt.Errorf("couldn't read file after %d retries", retryCount)
}
// writeAndRename opens tmpPath exclusively, writes data to it and renames it to p.
func (t *FSTree) writeAndRename(tmpPath, p string, data []byte) error {
err := t.writeFile(tmpPath, data)
if err != nil { if err != nil {
var pe *fs.PathError var pe *fs.PathError
if errors.As(err, &pe) && pe.Err == syscall.ENOSPC { if errors.As(err, &pe) {
err = common.ErrNoSpace switch pe.Err {
_ = os.RemoveAll(tmpPath) case syscall.ENOSPC:
err = common.ErrNoSpace
_ = os.RemoveAll(tmpPath)
case syscall.EEXIST:
return syscall.EEXIST
}
} }
} else { } else {
err = os.Rename(tmpPath, p) err = os.Rename(tmpPath, p)
} }
return err
return common.PutRes{StorageID: []byte{}}, err
} }
func (t *FSTree) writeFlags() int { func (t *FSTree) writeFlags() int {
flags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC flags := os.O_WRONLY | os.O_CREATE | os.O_TRUNC | os.O_EXCL
if t.noSync { if t.noSync {
return flags return flags
} }