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From Jan Lukavský (JIRA) <j...@apache.org>
Subject [jira] [Commented] (FLINK-8297) RocksDBListState stores whole list in single byte[]
Date Thu, 15 Mar 2018 15:25:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-8297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16400570#comment-16400570
] 

Jan Lukavský commented on FLINK-8297:
-------------------------------------

Yes, that seems related. I'm not 100% convinced that simply overcoming size limitation of
`Integer.MAX_VALUE` solves the actual problem, because the whole list would have to still
be stored in memory and can therefore result in various OOM errors, or containers being killed
(e.g. on YARN).

> RocksDBListState stores whole list in single byte[]
> ---------------------------------------------------
>
>                 Key: FLINK-8297
>                 URL: https://issues.apache.org/jira/browse/FLINK-8297
>             Project: Flink
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 1.4.0, 1.3.2
>            Reporter: Jan Lukavský
>            Priority: Major
>
> RocksDBListState currently keeps whole list of data in single RocksDB key-value pair,
which implies that the list actually must fit into memory. Larger lists are not supported
and end up with OOME or other error. The RocksDBListState could be modified so that individual
items in list are stored in separate keys in RocksDB and can then be iterated over. A simple
implementation could reuse existing RocksDBMapState, with key as index to the list and a single
RocksDBValueState keeping track of how many items has already been added to the list. Because
this implementation might be less efficient in come cases, it would be good to make it opt-in
by a construct like
> {{new RocksDBStateBackend().enableLargeListsPerKey()}}



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