Use BitSchemaPosting for schema keys.

- Make `dgraph debug --jepsen` work across predicate stripes.
- Sometimes it gets hard to debug, why we can't parse the PostingList.
Almost always, it is due to the fact that we came across a schema key.
We were not setting any UserMeta for it, so it was hard to determine the
root cause as well. This PR sets the UserMeta for schema keys, so
debugging is easier.

dgraph/cmd/debug/run.go

@@ -24,6 +24,7 @@ import (
 	"log"
 	"math"
 	"strconv"
+	"strings"
 
 	"github.com/dgraph-io/badger"
 	"github.com/dgraph-io/badger/options"
@@ -91,9 +92,13 @@ func readAmount(txn *badger.Txn, uid uint64) int {
 	itr := txn.NewIterator(iopt)
 	defer itr.Close()
 
-	key := x.DataKey("amount_0", uid)
-	for itr.Seek(key); itr.Valid(); {
+	for itr.Rewind(); itr.Valid(); {
 		item := itr.Item()
+		pk := x.Parse(item.Key())
+		if !pk.IsData() || pk.Uid != uid || !strings.HasPrefix(pk.Attr, "amount_") {
+			itr.Next()
+			continue
+		}
 		pl, err := posting.ReadPostingList(item.KeyCopy(nil), itr)
 		if err != nil {
 			log.Fatalf("Unable to read posting list: %v", err)
@@ -105,8 +110,12 @@ func readAmount(txn *badger.Txn, uid uint64) int {
 			times++
 			return nil
 		})
-		x.AssertTrue(times <= 1)
 		x.Check(err)
+		if times == 0 {
+			itr.Next()
+			continue
+		}
+		x.AssertTrue(times <= 1)
 		return amount
 	}
 	return 0
@@ -116,9 +125,6 @@ func seekTotal(db *badger.DB, readTs uint64) int {
 	txn := db.NewTransactionAt(readTs, false)
 	defer txn.Discard()
 
-	pk := x.ParsedKey{Attr: "key_0"}
-	prefix := pk.DataPrefix()
-
 	iopt := badger.DefaultIteratorOptions
 	iopt.AllVersions = true
 	iopt.PrefetchValues = false
@@ -127,14 +133,20 @@ func seekTotal(db *badger.DB, readTs uint64) int {
 
 	keys := make(map[uint64]int)
 	var lastKey []byte
-	for itr.Seek(prefix); itr.ValidForPrefix(prefix); {
+	for itr.Rewind(); itr.Valid(); {
 		item := itr.Item()
 		if bytes.Equal(lastKey, item.Key()) {
 			itr.Next()
 			continue
 		}
 		lastKey = append(lastKey[:0], item.Key()...)
 		pk := x.Parse(item.Key())
+		if !pk.IsData() || !strings.HasPrefix(pk.Attr, "key_") {
+			continue
+		}
+		if pk.IsSchema() {
+			continue
+		}
 
 		pl, err := posting.ReadPostingList(item.KeyCopy(nil), itr)
 		if err != nil {

posting/list.go

@@ -61,6 +61,7 @@ const (
 	Del uint32 = 0x02
 
 	// Metadata Bit which is stored to find out whether the stored value is pl or byte slice.
+	BitSchemaPosting   byte = 0x01
 	BitDeltaPosting    byte = 0x04
 	BitCompletePosting byte = 0x08
 	BitEmptyPosting    byte = 0x10 | BitCompletePosting

worker/mutation.go

@@ -226,7 +226,7 @@ func updateSchema(attr string, s pb.SchemaUpdate) error {
 	defer txn.Discard()
 	data, err := s.Marshal()
 	x.Check(err)
-	if err := txn.Set(x.SchemaKey(attr), data); err != nil {
+	if err := txn.SetWithMeta(x.SchemaKey(attr), data, posting.BitSchemaPosting); err != nil {
 		return err
 	}
 	return txn.CommitAt(1, nil)