I had a quick look at it, and we could do that, even for RocksDB: the method 
does a meta data lookup similar to what state registration does, remove the 
meta data and drop the column family. But until then, there is currently no 
complete dropping a keyed state.

> Am 22.02.2018 um 12:19 schrieb Stefan Richter <s.rich...@data-artisans.com>:
> Right now, I don’t think there is a way of doing that. I don’t think there is 
> something fundament against having a method that drops a state complete, data 
> and registered meta data. But so far that never existed and it seems nobody 
> ever needed it (or asked for it at least). The closest thing for keyed state 
> is calling the „clear()“ method, but the meta data will stick.
>> Am 22.02.2018 um 12:06 schrieb Gyula Fóra <gyula.f...@gmail.com>:
>> Do you have any suggestion how to completely delete an operator and keyed
>> state?
>> For operator state this seems to be easy enough, but what about completely
>> dropping a keyed state?
>> Gyula
>> Stefan Richter <s.rich...@data-artisans.com> ezt írta (időpont: 2018. febr.
>> 22., Cs, 11:46):
>>> Hi,
>>> I don’t think that this is a bug, but rather a necessity that comes with
>>> the (imo questionable) design of allowing lazy state registration. In this
>>> design, just because a state is *currently* not registered does not mean
>>> that you can simply drop it. Imagine that your code did *not yet*
>>> re-register a state, but could still do so in the future. If a
>>> checkpoint/recovery happens in between, all data for that state would
>>> suddenly be lost, just because by chance the state was not registered „fast
>>> enough“. As I see it, the proper way is the register the state under the
>>> same name and clear it if you want to get rid of the data. There is
>>> currently no call that explicitly drops a state that was once declared, and
>>> you might make a case that this is a feature to have for the future. Then
>>> again, we need a general decision about lazy and eager state IMO.
>>> Best,
>>> Stefan
>>>> Am 22.02.2018 um 11:10 schrieb Gyula Fóra <gyula.f...@gmail.com>:
>>>> Hi all,
>>>> We have discovered a fairly serious memory leak
>>>> in DefaultOperatorStateBackend, with broadcast (union) list states.
>>>> The problem seems to occur when a broadcast state name is changed, in
>>> order
>>>> to drop some state (intentionally).
>>>> Flink does not drop the "garbage" broadcast state, and keeps
>>> snapshotting,
>>>> broadcasting, multiplying it exponentially at every savepoint/restore
>>> cycle.
>>>> With high enough parallelism this can easily lead to small states (few
>>>> bytes) growing to several gigs and more over a few restarts eventually
>>>> leading to a very bad crash restart cycle where TMs OOM in a few secs.
>>>> Basically 2 things seems to be missing, garbage collection of
>>> unreferenced
>>>> operator states (they are eagerly restored into memory). And probably
>>> lazy
>>>> restore would also be nice :)
>>>> We run Flink 1.4.0 but 1.4.1 seems to be affected as well, haven't
>>> checked
>>>> the latest master.
>>>> Could someone please confirm that this behaviour is not as intended?
>>>> Cheers,
>>>> Gyula

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