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Posted to issues@flink.apache.org by "Flink Jira Bot (Jira)" <ji...@apache.org> on 2021/07/07 22:38:01 UTC
[jira] [Updated] (FLINK-19303) Disable WAL in RocksDB recovery
[ https://issues.apache.org/jira/browse/FLINK-19303?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Flink Jira Bot updated FLINK-19303:
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Labels: auto-deprioritized-major auto-unassigned (was: auto-unassigned stale-major)
Priority: Minor (was: Major)
This issue was labeled "stale-major" 7 days ago and has not received any updates so it is being deprioritized. If this ticket is actually Major, please raise the priority and ask a committer to assign you the issue or revive the public discussion.
> Disable WAL in RocksDB recovery
> -------------------------------
>
> Key: FLINK-19303
> URL: https://issues.apache.org/jira/browse/FLINK-19303
> Project: Flink
> Issue Type: Improvement
> Components: Runtime / State Backends
> Reporter: Juha Mynttinen
> Priority: Minor
> Labels: auto-deprioritized-major, auto-unassigned
>
> During recovery of {{RocksDBStateBackend}} the recovery mechanism puts the key value pairs to local RocksDB instance(s). To speed up the process, the recovery process uses RocskDB write batch mechanism. [RocksDB WAL|https://github.com/facebook/rocksdb/wiki/Write-Ahead-Log] is enabled during this process.
> During normal operations, i.e. when the state backend has been recovered and the Flink application is running (on RocksDB state backend) WAL is disabled.
> The recovery process doesn't need WAL. In fact the recovery should be much faster without WAL. Thus, WAL should be disabled in the recovery process.
> AFAIK the last thing that was done with WAL during recovery was an attempt to remove it. Later that removal was removed because it causes stability issues (https://issues.apache.org/jira/browse/FLINK-8922).
> Unfortunately the root cause why disabling WAL causes segfault during recovery is unknown. After all, WAL is not used during normal operations.
> Potential explanation is some kind of bug in RocksDB write batch when using WAL. It is possible later RocksDB versions have fixes / workarounds for the issue.
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