What causes "Empty value: %+v" in dgraph-io/badger?

Restore the data files from a known-good backup (LSM tree and .vlog files must come from the same snapshot).

Empty value: %+v

Error message

Empty value: %+v

What it means

This error is thrown during a value-log read (value.go:218) when the LSM tree says the key is still present (not discarded) but the returned ValueStruct carries a zero-length value, which should be impossible for a vlog-backed entry. It means the on-disk metadata pointing into the value log is inconsistent or truncated, so the read cannot return valid data.

Source

Thrown at value.go:218

		if count%100000 == 0 {
			vlog.opt.Debugf("Processing entry %d", count)
		}

		if isDeletedOrExpired(e.meta, e.ExpiresAt) {
			return nil
		}

		vs, err := vlog.db.get(e.Key)
		if err != nil {
			return err
		}
		if discardEntry(e, vs, vlog.db) {
			return nil
		}

		// Value is still present in value log.
		if len(vs.Value) == 0 {
			return fmt.Errorf("Empty value: %+v", vs)
		}
		var vp valuePointer
		vp.Decode(vs.Value)

		// If the entry found from the LSM Tree points to a newer vlog file, don't do anything.
		if vp.Fid > f.fid {
			return nil
		}
		// If the entry found from the LSM Tree points to an offset greater than the one
		// read from vlog, don't do anything.
		if vp.Offset > e.offset {
			return nil
		}
		// If the entry read from LSM Tree and vlog file point to the same vlog file and offset,
		// insert them back into the DB.
		// NOTE: It might be possible that the entry read from the LSM Tree points to
		// an older vlog file. See the comments in the else part.
		if vp.Fid == f.fid && vp.Offset == e.offset {

View on GitHub (pinned to 2a001d466f)

Solutions

Restore the data files from a known-good backup (LSM tree and .vlog files must come from the same snapshot).
Run badger StreamView/iterator to salvage readable keys, or use the badger 'db.ReplayValueLog' style recovery tooling for the affected vlog file.
Check whether value log files were truncated (compare sizes against value pointers); truncate/repair the offending .vlog with the badger repair tool if available.
If data is disposable, delete the affected .vlog files and let badger GC/rebuild, accepting loss of values still only in the vlog.
Verify the same badger library version is used for writing and reading the data directory.

Example fix

// before: copying DB dir partially
$ cp dbdir/MANIFEST dbdir/KEYREGISTRY dbdir/*.sst /backup/
// after: copy everything atomically (LSM + value log together)
$ badger backup --dir dbdir -f backup.bak
# or stop writes and copy the entire dbdir including *.vlog files

Defensive patterns

Strategy: try-catch

Validate before calling

// Go: verify the data directory is complete and consistent before opening
func checkVlogIntegrity(dir string) error {
    matches, err := filepath.Glob(filepath.Join(dir, "*.vlog"))
    if err != nil || len(matches) == 0 { return fmt.Errorf("no vlog files in %s", dir) }
    for _, m := range matches {
        fi, err := os.Stat(m)
        if err != nil || fi.Size() < 20 { return fmt.Errorf("vlog file %s missing or truncated", m) }
    }
    return nil
}

Type guard

func isEmptyValue(vs badger.ValueStruct) bool { return len(vs.Value) == 0 } // treat as corruption signal, not empty data

Try / catch

err := db.View(func(txn *badger.Txn) error {
    item, err := txn.Get(key)
    if err != nil { return err }
    return item.Value(func(v []byte) error {
        if len(v) == 0 { return fmt.Errorf("corrupt empty value for key %q", key) }
        return process(v)
    })
})
if err != nil {
    // fall back to backup/restore path; do not blind-retry
    restoreFromBackup(dbDir)
}

Prevention

Always snapshot the entire badger directory (MANIFEST, *.sst, *.vlog) atomically; never copy subsets.
Enable checksums/verify data directories after restore before serving traffic.
Use badger.Stream/backup+load for logical backups instead of raw file copies.
Run the same badger version that wrote the data.
Use fsync-backed storage and avoid force-killing the process (SIGKILL on write path).

When it happens

Trigger: Calling db.Get()/Txn.Get() on a key whose entry in the LSM points to the value log while vs.Value is empty; happens when value-log data was truncated/corrupted (e.g. crash without sync, partial file copy, badger.ValueLogMode misuse) or LSM/vlog files got out of sync.

Common situations: Restoring a database by copying only some files (LSM without vlog or vice versa), disk corruption or truncation after power loss, running an older badger version against data written by a newer one, manual deletion of .vlog files.

Related errors

AI-assisted analysis of dgraph-io/badger@2a001d466f (2026-09-05). Data as JSON: /api/errors/8d5bd3b43c5419cd. Report an issue: GitHub.