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https://issues.apache.org/jira/browse/CASSANDRA-12071?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcus Eriksson updated CASSANDRA-12071:
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Reviewer: Branimir Lambov
Fix Version/s: 3.9
Status: Patch Available (was: Open)
{{Flush}} runs on the flushExecutor and splits the memtable up based on the
number of data directories on the node and executes the {{FlushRunnable}}s on
the per disk flush executors. It then blocks until all per disk runnables are
completed to be able to run {{PostFlush}} etc.
Since {{flushExecutor}} size is 1 we can only ever execute a single flush at a
time.
Patch to bump it to {{memtable_flush_writers}}
[here|https://github.com/krummas/cassandra/commits/marcuse/12071] - in my tests
this removes the timeout issues
[~aweisberg] could you try it out?
[~blambov] to review since you might have some ideas for further improvements
> Regression in flushing throughput under load after CASSANDRA-6696
> -----------------------------------------------------------------
>
> Key: CASSANDRA-12071
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12071
> Project: Cassandra
> Issue Type: Bug
> Components: Local Write-Read Paths
> Reporter: Ariel Weisberg
> Assignee: Marcus Eriksson
> Fix For: 3.9
>
>
> The way flushing used to work is that a ColumnFamilyStore could have multiple
> Memtables flushing at once and multiple ColumnFamilyStores could flush at the
> same time. The way it works now there can be only a single flush of any
> ColumnFamilyStore & Memtable running in the C* process, and the number of
> threads applied to that flush is bounded by the number of disks in JBOD.
> This works ok most of the time but occasionally flushing will be a little
> slower and ingest will outstrip it and then block on available memory. At
> this point you see several second stalls that cause timeouts.
> This is a problem for reasonable configurations that don't use JBOD but have
> access to a fast disk that can handle some IO queuing (RAID, SSD).
> You can reproduce on beefy hardware (12 cores 24 threads, 64 gigs of RAM,
> SSD) if you unthrottle compaction or set it to something like 64
> megabytes/second and run with 8 compaction threads and stress with the
> default write workload and a reasonable number of threads. I tested with 96.
> It started happening after about 60 gigabytes of data was loaded.
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