What version of Go are you using (go version)?
$ go version go version go1.16 linux/amd64
What operating system are you using?
WSL on Windows
What version of Badger are you using?
v3.2103.0
Does this issue reproduce with the latest master?
Haven’t tested, but I don’t see any fixes in the changelog
Steps to Reproduce the issue
func TestBadgerPrefixRewind(t *testing.T) {
db, err := badger.Open(badger.DefaultOptions("").WithInMemory(true))
assert.NoError(t, err)
err = db.Update(func(txn *badger.Txn) error {
testMapping := map[string]byte{
"test1/abc": 0x1,
"test1/def": 0x2,
"test2/abc": 0x3,
"test2/def": 0x4,
"test3/abc": 0x5,
"test3/def": 0x6,
}
for key, value := range testMapping {
if err := txn.Set([]byte(key), []byte{value}); err != nil {
return err
}
}
return nil
})
assert.NoError(t, err)
options := badger.DefaultIteratorOptions
options.Prefix = []byte("test2/")
for _, reverse := range []bool{false, true} {
options.Reverse = reverse
_ = db.View(func(txn *badger.Txn) error {
it := txn.NewIterator(options)
defer it.Close()
it.Rewind()
fmt.Printf("reverse=%v\n", reverse)
fmt.Println("Starting item valid:", it.Valid())
if it.Item() != nil {
fmt.Println("Starting item key:", string(it.Item().Key()))
}
fmt.Println("All iterated keys:")
for ; it.Valid(); it.Next() {
fmt.Println(string(it.Item().Key()))
}
fmt.Println()
return nil
})
}
}
What Badger options were set?
Default options, in-memory (although problem exists with on-disk mode as well)
What did you do?
Set both reverse=true and a prefix on an iterator, then called Rewind()
What did you expect to see?
With reverse=false, it.Rewind() seeks to the smallest key matching the prefix (“test2/” in this case).
I would have expected reverse=true + it.Rewind() to seek to the largest key matching the prefix.
What did you see instead?
Test output:
reverse=false
Starting item valid: true
Starting item key: test2/abc
All iterated keys:
test2/abc
test2/def
reverse=true
Starting item valid: false
Starting item key: test1/def
All iterated keys:
it.Rewind() with reverse=true seeks to the largest key just before the start of the prefix. This means it.Valid() is false and it.Next() would only go backwards further past the prefix.