Compaction cleanupIfNecessary costly when many files in data dir
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Key: CASSANDRA-3532
URL: https://issues.apache.org/jira/browse/CASSANDRA-3532
Project: Cassandra
Issue Type: Bug
Affects Versions: 1.0.4
Environment: Solaris 10, 1.0.4 release candidate
Reporter: Eric Parusel
>From what I can tell SSTableWriter.cleanupIfNecessary seems increasingly
>costly as the number of files in the data dir increases.
It calls SSTable.componentsFor(descriptor, Descriptor.TempState.TEMP) which
lists all files in the data dir to find matching components.
Am I roughly correct that (cleanupCost = SSTable count * data dir size)?
We had been doing write load testing with default compaction throttling
(16MB/s) and LeveledCompaction.
Unfortunately we haven't been keeping tabs on sstable counts and it grew out of
control.
On a system with 300,000 sstables (!) here is an example of our compaction
rate. Note that as you're probably aware cleanupIfNecessary is included in the
timing:
INFO [CompactionExecutor:48] 2011-11-25 22:25:30,353 CompactionTask.java (line
213) Compacted to [/data1/cassandra/data/MA_DDR/indexes_03-hc-5369-Data.db,].
5,821,590 to 5,306,354 (~91% of original) bytes for 123 keys at 0.163755MB/s.
Time: 30,903ms.
Here's a slightly larger one:
INFO [CompactionExecutor:43] 2011-11-25 22:23:28,956 CompactionTask.java (line
213) Compacted to
[/data1/cassandra/data/MA_DDR/indexes_03-hc-5336-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5337-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5338-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5339-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5340-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5341-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5342-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5343-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5344-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5345-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5346-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5347-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5348-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5349-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5350-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5351-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5352-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5353-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5354-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5355-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5356-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5357-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5358-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5359-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5360-Data.db,/data1/cassandra/data/MA_DDR/indexes_03-hc-5361-Data.db,].
140,706,512 to 137,990,868 (~98% of original) bytes for 2,181 keys at
0.338627MB/s. Time: 388,623ms.
This is with compaction throttling set to 0 (Off).
So I believe because of this it's going to take a very long time to recover
from having so many small sstables.
It might be notable that we're using Solaris 10, possibly listFiles() is faster
on other platforms?
Is it feasible to keep track of the temp files and just delete them rather than
searching for them for each SSTable using SSTable.componentsFor()?
Here's the stack trace for the CompactionExecutor:14 thread that appears to be
occupying the majority of the cpu time on this node:
Name: CompactionExecutor:14
State: RUNNABLE
Total blocked: 3 Total waited: 1,610,714
Stack trace:
java.io.UnixFileSystem.getBooleanAttributes0(Native Method)
java.io.UnixFileSystem.getBooleanAttributes(Unknown Source)
java.io.File.isDirectory(Unknown Source)
org.apache.cassandra.io.sstable.SSTable$3.accept(SSTable.java:204)
java.io.File.listFiles(Unknown Source)
org.apache.cassandra.io.sstable.SSTable.componentsFor(SSTable.java:200)
org.apache.cassandra.io.sstable.SSTableWriter.cleanupIfNecessary(SSTableWriter.java:289)
org.apache.cassandra.db.compaction.CompactionTask.execute(CompactionTask.java:189)
org.apache.cassandra.db.compaction.LeveledCompactionTask.execute(LeveledCompactionTask.java:57)
org.apache.cassandra.db.compaction.CompactionManager$1.call(CompactionManager.java:134)
org.apache.cassandra.db.compaction.CompactionManager$1.call(CompactionManager.java:114)
java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
java.util.concurrent.FutureTask.run(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
java.lang.Thread.run(Unknown Source)
No matter where I click in the busy Compaction thread timeline in YourKit it's
in Running state and showing this above trace, except for short periods of time
where it's actually compacting :)
Thanks,
Eric
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