J.B. Langston created CASSANDRA-10593:
-----------------------------------------
Summary: Unintended interactions between commitlog archiving and
commitlog recycling
Key: CASSANDRA-10593
URL: https://issues.apache.org/jira/browse/CASSANDRA-10593
Project: Cassandra
Issue Type: Bug
Reporter: J.B. Langston
Currently the comments in commitlog_archiving.properties suggest using either
cp or ln for the archive_command.
Using ln is problematic because commitlog recycling marks segments as recycled
once the corresponding memtables are flushed and Cassandra will no longer be
replay them. This means it's only possible to do PITR on any records that were
written since the last flush.
Using cp works, and this is currently how OpsCenter does for PITR, however
[~brandon.williams] has pointed out this could have some performance impact
because of the additional I/O overhead of copying the commitlog segments.
Starting in 2.1, we can disable commit log recycling in cassandra.yaml so I
thought this would allow me to do PITR without the extra overhead of using cp.
However, when I disable commitlog recycling and try to do a PITR, Cassandra
blows up when trying to replay the restored commit logs:
{code}
ERROR 16:56:42 Exception encountered during startup
java.lang.IllegalStateException: Cannot safely construct descriptor for
segment, as name and header descriptors do not match ((4,1445878452545) vs
(4,1445876822565)): /opt/dse/backup/CommitLog-4-1445876822565.log
at
org.apache.cassandra.db.commitlog.CommitLogArchiver.maybeRestoreArchive(CommitLogArchiver.java:207)
~[cassandra-all-2.1.9.791.jar:2.1.9.791]
at
org.apache.cassandra.db.commitlog.CommitLog.recover(CommitLog.java:116)
~[cassandra-all-2.1.9.791.jar:2.1.9.791]
at
org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.java:352)
~[cassandra-all-2.1.9.791.jar:2.1.9.791]
at com.datastax.bdp.server.DseDaemon.setup(DseDaemon.java:335)
~[dse-core-4.8.0.jar:4.8.0]
at
org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon.java:537)
~[cassandra-all-2.1.9.791.jar:2.1.9.791]
at com.datastax.bdp.DseModule.main(DseModule.java:75)
[dse-core-4.8.0.jar:4.8.0]
java.lang.IllegalStateException: Cannot safely construct descriptor for
segment, as name and header descriptors do not match ((4,1445878452545) vs
(4,1445876822565)): /opt/dse/backup/CommitLog-4-1445876822565.log
at
org.apache.cassandra.db.commitlog.CommitLogArchiver.maybeRestoreArchive(CommitLogArchiver.java:207)
at
org.apache.cassandra.db.commitlog.CommitLog.recover(CommitLog.java:116)
at
org.apache.cassandra.service.CassandraDaemon.setup(CassandraDaemon.java:352)
at com.datastax.bdp.server.DseDaemon.setup(DseDaemon.java:335)
at
org.apache.cassandra.service.CassandraDaemon.activate(CassandraDaemon.java:537)
at com.datastax.bdp.DseModule.main(DseModule.java:75)
Exception encountered during startup: Cannot safely construct descriptor for
segment, as name and header descriptors do not match ((4,1445878452545) vs
(4,1445876822565)): /opt/dse/backup/CommitLog-4-1445876822565.log
INFO 16:56:42 DSE shutting down...
INFO 16:56:42 All plugins are stopped.
ERROR 16:56:42 Exception in thread Thread[Thread-2,5,main]
java.lang.AssertionError: null
at
org.apache.cassandra.gms.Gossiper.addLocalApplicationState(Gossiper.java:1403)
~[cassandra-all-2.1.9.791.jar:2.1.9.791]
at com.datastax.bdp.gms.DseState.setActiveStatus(DseState.java:196)
~[dse-core-4.8.0.jar:4.8.0]
at com.datastax.bdp.server.DseDaemon.preStop(DseDaemon.java:426)
~[dse-core-4.8.0.jar:4.8.0]
at com.datastax.bdp.server.DseDaemon.safeStop(DseDaemon.java:436)
~[dse-core-4.8.0.jar:4.8.0]
at com.datastax.bdp.server.DseDaemon$1.run(DseDaemon.java:676)
~[dse-core-4.8.0.jar:4.8.0]
at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_31]
{code}
For the sake of completeness, I also tested using cp for the archive_command
and commitlog recycling disabled, and PITR works as expected, but this of
course defeats the point.
It would be good to have some guidance on what is supported here. If ln isn't
expected to work at all, it shouldn't be documented as an acceptable option for
the archive_command in commitlog_archiving.properties. If it should work with
commitlog recycling disabled, the bug causing the IllegalStateException needs
to be fixed.
It would also be good to do some testing and quantify the performance impact of
enabling commitlog archiving using cp as the archve_command.
I realize there are several different issues described here, so maybe they
should be separate JIRAs, but first I wanted to just clarify whether we want to
support ln at all, and we can go from there.
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