snapshots seem not to work

[juliangruber]

this test (simplified for this issue):

test('iterator create snapshot correctly', function (t) {
    db.put('foobatch1', 'bar1', function(err){
      t.error(err)
      var iterator = db.iterator()
      db.del('foobatch1', function () {
        iterator.next(function (err, key, value) {
          t.notOk(err, 'no error')
          t.ok(key, 'got a key')
          t.equal(key.toString(), 'foobatch1', 'correct key')
          t.equal(value.toString(), 'bar1', 'correct value')
          iterator.end(t.end.bind(t))
        })
      })
    })
  })

is failing:

# iterator create snapshot correctly
default_stream.js:27 ok 419 no error
default_stream.js:27 not ok 420 got a key
default_stream.js:27   ---
default_stream.js:27     operator: ok
default_stream.js:27     expected: true
default_stream.js:27     actual:   undefined
default_stream.js:27     at: Test.assert (http://localhost:9966/test.js:12977:17)
default_stream.js:27   ...
iterator-test.js:467 Uncaught TypeError: Cannot read property 'toString' of undefined

@maxogden do you know what's going on here?

[ralphtheninja]

@juliangruber Just noticed this myself while trying to bring level.js up to par on abstract-levelown. It seems that it doesn't have support for snapshots and that needs to be implemented.

I checked memdown and it seems it grabs the tree from the db, which I think is why it works well for memdown, see https://github.com/Level/memdown/blob/19ed79fbf853571098b6475d8c79c10ca6f22d4b/memdown.js#L36

[juliangruber]

Can we implement snapshots after we bring the rest up to par? It seems like this is it's own good chunk of work.

[vweevers]

The thing with IndexedDB is that you can't have both snapshots and proper backpressure. Details in the thread starting here: #46 (comment)

[vweevers]

I checked memdown and it seems it grabs the tree from the db, which I think is why it works well for memdown

Memdown is a different story. It works because it's backed by functional-red-black-tree which is a persistent data structure. I.e. iteration happens on an immutable tree, unaffected by simultaneous writes.