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https://issues.apache.org/jira/browse/FLINK-9070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16417588#comment-16417588
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Sihua Zhou commented on FLINK-9070:
-----------------------------------
Hi [~kien_truong] Thanks for sharing the code and now I have a good understand
the optimization solution you proposed using {{deleteRange()}}. I only have two
question:
- From the
[comment|https://github.com/facebook/rocksdb/blob/master/include/rocksdb/db.h#L284-L299]
in RocksDB's source we can find that deleteRange() should be used for deleting
big range, what if the entries num of the map is not that big?
- From the comments we can also find that deleteRange() would hurt the read
performance, so we should consider to set ReadOptions::ignore_range_deletions =
true to avoid the negative effect by {{deleteRange()}}, but if we use it for
MapState.clear(), it seems that we can't set
ReadOptions::ignore_range_deletions = true?
> Improve performance of RocksDBMapState.clear()
> ----------------------------------------------
>
> Key: FLINK-9070
> URL: https://issues.apache.org/jira/browse/FLINK-9070
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Affects Versions: 1.6.0
> Reporter: Truong Duc Kien
> Priority: Minor
>
> Currently, RocksDBMapState.clear() is implemented by iterating over all the
> keys and drop them one by one. This iteration can be quite slow with:
> * Large maps
> * High-churn maps with a lot of tombstones
> There are a few methods to speed-up deletion for a range of keys, each with
> their own caveats:
> * DeleteRange: still experimental, likely buggy
> * DeleteFilesInRange + CompactRange: only good for large ranges
>
> Flink can also keep a list of inserted keys in-memory, then directly delete
> them without having to iterate over the Rocksdb database again.
>
> Reference:
> * [RocksDB article about range
> deletion|https://github.com/facebook/rocksdb/wiki/Delete-A-Range-Of-Keys]
> * [Bug in DeleteRange|https://pingcap.com/blog/2017-09-08-rocksdbbug]
>
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