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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-9194) Delete-only workloads crash Cassandra
Date Wed, 22 Apr 2015 14:06:59 GMT


Benedict commented on CASSANDRA-9194:

[~jbellis]: I was referring to the behaviour in 2.1, in which we still track the live size
from 2.0, but only for informational purposes. It's kind of arbitrary and definitely storage
layer dependent (so subject to change), whereas in 2.0 I wanted to affect existing behaviour
minimally. I'm a little tempted to suggest we drop the live size tracking entirely in 3.0.
In the meantime we could just always count 8 bytes for the row marker, although arguably we
should really be counting the partition key bytes as well. I have literally no opinion for

> Delete-only workloads crash Cassandra
> -------------------------------------
>                 Key: CASSANDRA-9194
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>         Environment: 2.0.14
>            Reporter: Robert Wille
>            Assignee: Benedict
>             Fix For: 2.0.15
>         Attachments: 9194.txt
> The size of a tombstone is not properly accounted for in the memtable. A memtable which
has only tombstones will never get flushed. It will grow until the JVM runs out of memory.
The following program easily demonstrates the problem.
> {code}
> 		Cluster.Builder builder = Cluster.builder();
> 		Cluster c = builder.addContactPoints("").build();
> 		Session s = c.connect();
> 		s.execute("CREATE KEYSPACE IF NOT EXISTS test WITH replication = { 'class' : 'SimpleStrategy',
'replication_factor' : 1 }");
> 		s.execute("CREATE TABLE IF NOT EXISTS test.test(id INT PRIMARY KEY)");
> 		PreparedStatement stmt = s.prepare("DELETE FROM test.test WHERE id = :id");
> 		int id = 0;
> 		while (true)
> 		{
> 			s.execute(stmt.bind(id));
> 			id++;
> 		}{code}
> This program should run forever, but eventually Cassandra runs out of heap and craps
out. You needn't wait for Cassandra to crash. If you run "nodetool cfstats test.test" while
it is running, you'll see Memtable cell count grow, but Memtable data size will remain 0.
> This issue was fixed once before. I received a patch for version 2.0.5 (I believe), which
contained the fix, but the fix has apparently been lost, because it is clearly broken, and
I don't see the fix in the change logs.

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