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fallback on etags if they match when mtime is not same (#17424)

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on "unversioned" buckets there are situations
when successive concurrent I/O can lead to
an inconsistent state() with mtime while the
etag might be the same for the object on disk.

in such a scenario it is possible for us to
allow reading of the object since etag matches
and if etag matches we are guaranteed that we
have enough copies the object will be readable
and same.

This PR allows fallback in such scenarios.
This commit is contained in:
Harshavardhana
2023-06-17 19:18:20 -07:00
committed by GitHub
parent 22b7c8cd8a
commit 64de61d15d
7 changed files with 117 additions and 30 deletions
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18
cmd/erasure-metadata.go
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@@ -328,7 +328,7 @@ func (fi FileInfo) ObjectToPartOffset(ctx context.Context, offset int64) (partIn
return 0, 0, InvalidRange{}
}
func findFileInfoInQuorum(ctx context.Context, metaArr []FileInfo, modTime time.Time, quorum int) (FileInfo, error) {
func findFileInfoInQuorum(ctx context.Context, metaArr []FileInfo, modTime time.Time, etag string, quorum int) (FileInfo, error) {
// with less quorum return error.
if quorum < 1 {
return FileInfo{}, errErasureReadQuorum
@@ -336,9 +336,17 @@ func findFileInfoInQuorum(ctx context.Context, metaArr []FileInfo, modTime time.
metaHashes := make([]string, len(metaArr))
h := sha256.New()
for i, meta := range metaArr {
if meta.IsValid() && meta.ModTime.Equal(modTime) {
if !meta.IsValid() {
continue
}
etagOnly := modTime.Equal(timeSentinel) && (etag != "" && etag == meta.Metadata["etag"])
mtimeValid := meta.ModTime.Equal(modTime)
if mtimeValid || etagOnly {
fmt.Fprintf(h, "%v", meta.XLV1)
fmt.Fprintf(h, "%v", meta.GetDataDir())
if !etagOnly {
// Verify dataDir is same only when mtime is valid and etag is not considered.
fmt.Fprintf(h, "%v", meta.GetDataDir())
}
for _, part := range meta.Parts {
fmt.Fprintf(h, "part.%d", part.Number)
}
@@ -408,8 +416,8 @@ func pickValidDiskTimeWithQuorum(metaArr []FileInfo, quorum int) time.Time {
// pickValidFileInfo - picks one valid FileInfo content and returns from a
// slice of FileInfo.
func pickValidFileInfo(ctx context.Context, metaArr []FileInfo, modTime time.Time, quorum int) (FileInfo, error) {
return findFileInfoInQuorum(ctx, metaArr, modTime, quorum)
func pickValidFileInfo(ctx context.Context, metaArr []FileInfo, modTime time.Time, etag string, quorum int) (FileInfo, error) {
return findFileInfoInQuorum(ctx, metaArr, modTime, etag, quorum)
}
// writeUniqueFileInfo - writes unique `xl.meta` content for each disk concurrently.