[jira] [Commented] (FLINK-9070) Improve performance of RocksDBMapState.clear()

["Sihua Zhou (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-9070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16429383#comment-16429383 ] 

Sihua Zhou commented on FLINK-9070:
-----------------------------------

Hi [~kien_truong] I also share my idea for improving this here
[https://github.com/sihuazhou/flink/commit/6ff501416487608633e19aea7ff32c181e6e09b7|https://github.com/sihuazhou/flink/commit/6ff501416487608633e19aea7ff32c181e6e09b7]

It base on the follow things
- Using RocksIterator to iterate the records directly (currently we use the RocksDBMapIterator, witch will buffer the records and may also need to perform seeking multi times.)
- Using WriteBatch to perform deleting in bulk.

What do you think?


> 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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