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https://issues.apache.org/jira/browse/CASSANDRA-2142?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12992191#comment-12992191
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Stu Hood commented on CASSANDRA-2142:
-------------------------------------
For a 128 M heap, and a 255 M memtable, I had to tune {{reduce_heap_usage_at}}
down to 0.66 to get the flushes to trigger at all.
Once they did trigger, it appeared that they frequently triggered twice, such
that we ended up flushing a small memtable, like so:
{noformat} INFO 13:13:45,198 GC for ConcurrentMarkSweep: 694 ms, 22626024
reclaimed leaving 264991288 used; max is 403505152
INFO 13:13:47,021 GC for ConcurrentMarkSweep: 865 ms, 20137408 reclaimed
leaving 267475352 used; max is 403505152
WARN 13:13:47,022 Flushing
ColumnFamilyStore(table='org.apache.cassandra.db.Table@68e26d2e',
columnFamily='Standard1') and
ColumnFamilyStore(table='org.apache.cassandra.db.Table@68e26d2e',
columnFamily='Standard1') to relieve memory pressure
INFO 13:13:47,024 switching in a fresh Memtable for Standard1 at
CommitLogContext(file='/var/lib/cassandra/commitlog/CommitLog-1297199505461.log',
position=122618113)
INFO 13:13:47,025 Enqueuing flush of Memtable-Standard1@1628970020(3822960
bytes, 74960 operations)
INFO 13:13:48,824 GC for ConcurrentMarkSweep: 802 ms, 19015584 reclaimed
leaving 268597464 used; max is 403505152
WARN 13:13:48,824 Flushing
ColumnFamilyStore(table='org.apache.cassandra.db.Table@68e26d2e',
columnFamily='Standard1') and
ColumnFamilyStore(table='org.apache.cassandra.db.Table@68e26d2e',
columnFamily='Standard1') to relieve memory pressure
INFO 13:13:48,842 switching in a fresh Memtable for Standard1 at
CommitLogContext(file='/var/lib/cassandra/commitlog/CommitLog-1297199505461.log',
position=122904861)
INFO 13:13:48,842 Enqueuing flush of Memtable-Standard1@821726121(137445
bytes, 2695 operations)
INFO 13:13:53,160 Completed flushing
/var/lib/cassandra/data/Keyspace1/Standard1-f-8-Data.db (18975528 bytes)
INFO 13:13:53,161 Writing Memtable-Standard1@1628970020(3822960 bytes, 74960
operations){noformat}
Finally, the node ended up going OOM before the end of the stress.py run.
> Add "reduce memory usage because I tuned things poorly" feature
> ---------------------------------------------------------------
>
> Key: CASSANDRA-2142
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2142
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Priority: Minor
> Labels: ponies
> Fix For: 0.7.1
>
> Attachments: 2142.txt
>
>
> Users frequently create too many columnfamilies, set the memtable thresholds
> too high (or adjust throughput while ignoring operations), and/or set caching
> thresholds too high. Then their server OOMs and they tell their friends
> Cassandra sucks.
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