Can't create a valid WAL iterator

[Hayden Parker]

In the following trivial example, I attempt to get a WAL iterator on a database using the latest sequence number.

package main

import (
	log "github.com/sirupsen/logrus"
	"github.com/tecbot/gorocksdb"
)

func main() {
	opts := gorocksdb.NewDefaultOptions()
	opts.SetCreateIfMissing(true)
	testDB, err := gorocksdb.OpenDb(opts, "test")
	if err != nil {
		log.WithFields(log.Fields{
			"error": err.Error(),
		}).Error("error opening database")
		return
	}

	lastSequence := testDB.GetLatestSequenceNumber()
	walIter, err := testDB.GetUpdatesSince(lastSequence)

	if err != nil {
		log.WithFields(log.Fields{
			"error":    err.Error(),
			"sequence": lastSequence,
		}).Error("error getting WAL iterator")
		return
	}
	if walIter == nil {
		log.WithFields(log.Fields{
			"sequence": lastSequence,
		}).Error("WAL iterator is nil")
		return
	}
	if walIter.Err() != nil {
		log.WithFields(log.Fields{
			"error":    walIter.Err(),
			"sequence": lastSequence,
		}).Error("WAL iterator has an error")
		return
	}
	if !walIter.Valid() {
		log.WithFields(log.Fields{
			"sequence": lastSequence,
		}).Error("WAL iterator is not valid")
		return
	}
}

Running this code produces the following:

ERRO[0000] WAL iterator is not valid                     sequence=0

I've also done more complex examples, where I've loaded some data and the sequence is not 0, but I still get an invalid iterator.

Unless I'm missing something, this seems like a bug in gorocksdb, or rocksdb itself? I'm using arch to install rocksdb, which brought down version 6.5.3-1. Gorocksdb built just fine, but based on this I'm thinking maybe it's a version issue. I'll try to build on an 5.X version and see what happens (though it would be great to be on >= 6.2.2 so I don't have to backport the fix for the memory leak).

[Hayden Parker]

Reproduced this in an ubuntu docker container using librocksdb-dev, which is version 5.17.2-3

[Hayden Parker]

Seems like it's invalid if there's no data in it. A write just before getting the WAL iterator results in a valid iterator.