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https://issues.apache.org/jira/browse/CASSANDRA-11697?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15365050#comment-15365050
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T Jake Luciani edited comment on CASSANDRA-11697 at 7/6/16 8:53 PM:
--------------------------------------------------------------------
Just a general note about my findings so far:
There seems to be some conflation about the performance of compaction mainly
that low IO is slower than high IO. Our compaction is primarily CPU bound and
since we compress by default it can appear that compaction is going slow but
it's actually doing ~the same rows/sec as uncompressed. Here is an example of
compressed vs uncompressed notice the new log message from CASSANDRA-10805
shows ~ the same rows/sec.
{quote}
#UNCOMPRESSED
INFO 20:22:01 Compacted (3206a030-43b7-11e6-bf87-63e169949442) 2 sstables to
[/home/jake/workspace/cassandra/build/test/cassandra/data/cql_keyspace/table1-041d8b2043b711e6bf8763e169949442/mb-3-big,]
to level=0.
782.013MiB to 361.930MiB (~46% of original) in 43,211ms.
Read Throughput = 18.097MiB/s, Write Throughput = 8.376MiB/s,
Row Throughput = ~454,545/s. 20,000,000 total partitions merged to
10,000,000. Partition merge counts were \{2:10000000, \}
#COMPRESSED
INFO 20:27:49 Compacted (00d23b40-43b8-11e6-ad90-8f9393166cb4) 2 sstables to
[/home/jake/workspace/cassandra/build/test/cassandra/data/cql_keyspace/table1-da46ad8043b711e6ad908f9393166cb4/mb-3-big,]
to level=0.
123.201MiB to 57.405MiB (~46% of original) in 44,527ms. Read Throughput =
2.767MiB/s, Write Throughput = 1.289MiB/s,
Row Throughput = ~444,444/s. 20,000,000 total partitions merged to
10,000,000. Partition merge counts were \{2:10000000,\}
{quote}
*I'd like to start talking about compaction in terms of row throughput vs
MB/sec.*
There are some things we can do to make our current compaction faster like
CASSANDRA-10309 should give us a ~10% boost but the *bigger* issue and what I
think most users are seeing in the real world is the fact that under load
compaction effectively grinds to a halt. I can easily produce a 10x drop in
throughput by applying load during a regular compaction. This to me is the
problem we should be focused on since we can see this when looking at sample
user logs. I have a POC I'm working on to address this that I'll be presenting
soon.
was (Author: tjake):
Just a general note about my findings so far:
There seems to be some conflation about the performance of compaction mainly
that low IO is slower than high IO. Our compaction is primarily CPU bound and
since we compress by default it can appear that compaction is going slow but
it's actually doing ~the same rows/sec as uncompressed. Here is an example of
compressed vs uncompressed notice the new log message from CASSANDRA-10805
shows ~ the same rows/sec.
{quote}
#UNCOMPRESSED
INFO 20:22:01 Compacted (3206a030-43b7-11e6-bf87-63e169949442) 2 sstables to
[/home/jake/workspace/cassandra/build/test/cassandra/data/cql_keyspace/table1-041d8b2043b711e6bf8763e169949442/mb-3-big,]
to level=0.
782.013MiB to 361.930MiB (~46% of original) in 43,211ms.
Read Throughput = 18.097MiB/s, Write Throughput = 8.376MiB/s,
Row Throughput = ~454,545/s. 20,000,000 total partitions merged to
10,000,000. Partition merge counts were {2:10000000, }
#COMPRESSED
INFO 20:27:49 Compacted (00d23b40-43b8-11e6-ad90-8f9393166cb4) 2 sstables to
[/home/jake/workspace/cassandra/build/test/cassandra/data/cql_keyspace/table1-da46ad8043b711e6ad908f9393166cb4/mb-3-big,]
to level=0.
123.201MiB to 57.405MiB (~46% of original) in 44,527ms. Read Throughput =
2.767MiB/s, Write Throughput = 1.289MiB/s,
Row Throughput = ~444,444/s. 20,000,000 total partitions merged to
10,000,000. Partition merge counts were {2:10000000, }
{quote}
*I'd like to start talking about compaction in terms of row throughput vs
MB/sec.*
There are some things we can do to make our current compaction faster like
CASSANDRA-10309 should give us a ~10% boost but the *bigger* issue and what I
think most users are seeing in the real world is the fact that under load
compaction effectively grinds to a halt. I can easily produce a 10x drop in
throughput by applying load during a regular compaction. This to me is the
problem we should be focused on since we can see this when looking at sample
user logs. I have a POC I'm working on to address this that I'll be presenting
soon to address this.
> Improve Compaction Throughput
> -----------------------------
>
> Key: CASSANDRA-11697
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11697
> Project: Cassandra
> Issue Type: Improvement
> Components: Compaction
> Reporter: T Jake Luciani
> Assignee: T Jake Luciani
>
> The goal of this ticket is to improve/understand the bottlenecks during
> compactions. At a high level this will involve:
> * A test system for measuring compaction time for different workloads and
> compaction strategies.
> * Profiling and analysis
> * Make improvements
> * Add throughput regression tests so we can track
> We have a lot of random tickets that relate to this so I'll link them to this
> ticket
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