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https://issues.apache.org/jira/browse/CASSANDRA-19569?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mykyta Bozhenko updated CASSANDRA-19569:
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Status: Patch Available (was: Open)
> sstableupgrade is very slow
> ---------------------------
>
> Key: CASSANDRA-19569
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19569
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/Compaction
> Reporter: Norbert Schultz
> Assignee: Mykyta Bozhenko
> Priority: Normal
> Fix For: 4.1.x
>
> Attachments: flamegraph_ok.png, flamegraph_sstableupgrade.png
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> We are in the process of migrating cassandra from 3.11.x to 4.1.4 and
> upgrading the sstables using sstableupgrade from Cassandra V4.1.4, from `me-`
> to `nb-` Format
> Unfortunately, the process is very very slow (less than 0.5 MB/s).
> Some observations:
> - The process is only slow on (fast) SSDs, but not on ram disks.
> - The sstables consist of many partitions (this may be unrelated)
> - The upgrade process is fast, if we use `automatic_sstable_upgrade` instead
> of the sstableupgradetool.
> - We give enough RAM (export MAX_HEAP_SIZE=8g)
> On profiling, we found out, that sstableupgrade is burning most CPU time on
> {{posix_fadvise}} (see flamegraph_sstableupgrade.png ).
> My naive interpretation of the whole {{maybeReopenEarly}} to
> {{posix_fadvise}} chain is, that the process just informs the linux kernel,
> that the written data should not be cached. If we comment out the call to
> {{NativeLibrary.trySkipCache}}, the conversion is running at expected 10MB/s
> (see flamegraph_ok.png )
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