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https://issues.apache.org/jira/browse/CASSANDRA-12114?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Shuler updated CASSANDRA-12114:
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Fix Version/s: (was: 3.9)
3.8
> Cassandra startup takes an hour because of N*N operation
> --------------------------------------------------------
>
> Key: CASSANDRA-12114
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12114
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: Tom van der Woerdt
> Assignee: Jeff Jirsa
> Labels: lcs, performance
> Fix For: 3.0.9, 3.8
>
>
> (There's a previous version of this ticket, which was very wrong about the
> actual cause. Original is quoted below)
> In java.org.cassandra.db.ColumnFamilyStore, the function scrubDataDirectories
> loops over all sstables and then for each sstable it cleans temporary files
> from its directory.
> Since there are many sstables in a directory, this ends up cleaning the same
> directory many times.
> When using leveledcompactionstrategy on a data set that is ~4TB per node, you
> can easily end up with 200k files.
> Add N and N, and we get a N*N operation (scrubDataDirectories) which ends up
> taking an hour (or more).
> (At this point I should probably point out that no, I am not sure about that.
> At all. But I do know this takes an hour and jstack blames this function)
> As promised, original ticket below :
> {quote}
> A Cassandra cluster of ours has nodes with up to 4TB of data, in a single
> table using leveled compaction having 200k files. While upgrading from 2.2.6
> to 3.0.7 we noticed that it took a while to restart a node. And with "a
> while" I mean we measured it at more than 60 minutes.
> jstack shows something interesting :
> {code}
> "main" #1 prio=5 os_prio=0 tid=0x00007f30db0ea400 nid=0xdb22 runnable
> [0x00007f30de122000]
> java.lang.Thread.State: RUNNABLE
> at java.io.UnixFileSystem.list(Native Method)
> at java.io.File.list(File.java:1122)
> at java.io.File.listFiles(File.java:1248)
> at
> org.apache.cassandra.io.sstable.Descriptor.getTemporaryFiles(Descriptor.java:172)
> at
> org.apache.cassandra.db.ColumnFamilyStore.scrubDataDirectories(ColumnFamilyStore.java:599)
> at
> org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.java:245)
> at
> org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon.java:557)
> at
> org.apache.cassandra.service.CassandraDaemon.main(CassandraDaemon.java:685)
> {code}
> Going by the source of File.listFiles, it puts every file in a directory into
> an array and *then* applies the filter.
> This is actually a known Java issue from 1999:
> http://bugs.java.com/view_bug.do?bug_id=4285834 -- their "solution" was to
> introduce new APIs in JRE7. I guess that makes listFiles deprecated for
> larger directories (like when using LeveledCompactionStrategy).
> tl;dr: because Cassandra uses java.io.File.listFiles, service startup can
> take an hour for larger data sets.
> {quote}
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