A problem about Rocksdb deleting data but after that iterator still iterate old data

I made an experiment to figure out a rocksdb problem while developing a system using pyrocksdb. I tried the code below:

def func(iterator):
     for k, v in iterator:
             print("k:{}, v:{}".format(k, v))

import rocksdb
db = rocksdb.DB("test.db", rocksdb.Options(create_if_missing=True))
batch = rocksdb.WriteBatch()
batch.put(b'a1', b'data1')
batch.put(b'a2', b'data2')
batch.put(b'a3', b'data3')
db.write(batch)
it = db.iteritems()
it.seek_to_first()
func(it)

#print info
k:b'a1', v:b'data1'
k:b'a2', v:b'data2'
k:b'a3', v:b'data3'

#delete a kv
db.delete(b'a1')
it.seek_to_first()
func(it)

#print info, k:b'a1', v:b'data1' is still available
k:b'a1', v:b'data1'
k:b'a2', v:b'data2'
k:b'a3', v:b'data3'

#but if I reassign it
it = db.iteritems()
it.seek_to_first()
func(it)

#print info, delete takes effect
k:b'a2', v:b'data2'
k:b'a3', v:b'data3'

I want to figure out why I need to reassign the iterator?

Solution

Reason:

First called db.iteritems() and the returned value is stored in it.
Even after you have deleted using db.delete(b'a1'), the information stored in it doesn't updated. It will be same as before.
But to check, again you need to update the information of it variable (which you have done by in your last case) by doing it = db.iteritems().
Now it variable is updated, and you can see the data is deleted as well.

Solution:

Create a function to do that repetitive task and you can call it, whenever you want to print the data.

def update_func():
    it = db.iteritems()
    it.seek_to_first()
    func(it)

update_func()