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https://issues.apache.org/jira/browse/CASSANDRA-2829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13064643#comment-13064643
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Jonathan Ellis commented on CASSANDRA-2829:
-------------------------------------------
Thinking out loud here.
CLHeader has a structure to tell us "do we need to replay, and if so, from
where?"
{code}
private Map<Integer, Integer> cfDirtiedAt; // position at which each CF was
last flushed
boolean isDirty(Integer cfId)
{
return cfDirtiedAt.containsKey(cfId);
}
boolean isDirty(Integer cfId)
{
return cfDirtiedAt.containsKey(cfId);
}
{code}
This is set in two places. One is during a write:
{code}
if (!header.isDirty(id))
{
header.turnOn(id, logWriter.getFilePointer());
writeHeader();
}
{code}
The other is post-flush, as described above:
{code}
if (segment.equals(context.getSegment()))
{
// we can't just mark the segment where the flush happened
clean,
// since there may have been writes to it between when the flush
// started and when it finished. so mark the flush position as
// the replay point for this CF, instead.
if (logger.isDebugEnabled())
logger.debug("Marking replay position " + context.position
+ " on commit log " + segment);
header.turnOn(id, context.position);
segment.writeHeader();
break;
}
{code}
It feels like we need to add a "most recent write at" information as well as
the "oldest write/replay position at" one. This would not need to be persisted
to disk.
(I thought that this is what 0.6 did, but looking at it that is not the case.
So this bug is present there as well, but I think at this point it just needs
to be a known bug there. Maybe even for 0.7.)
> always flush memtables
> ----------------------
>
> Key: CASSANDRA-2829
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2829
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 0.7.0
> Reporter: Aaron Morton
> Assignee: Aaron Morton
> Fix For: 0.7.8
>
> Attachments: 0001-2829-unit-test.patch, 0002-2829.patch
>
>
> Only dirty Memtables are flushed, and so only dirty memtables are used to
> discard obsolete commit log segments. This can result it log segments not
> been deleted even though the data has been flushed.
> Was using a 3 node 0.7.6-2 AWS cluster (DataStax AMI's) with pre 0.7 data
> loaded and a running application working against the cluster. Did a rolling
> restart and then kicked off a repair, one node filled up the commit log
> volume with 7GB+ of log data, there was about 20 hours of log files.
> {noformat}
> $ sudo ls -lah commitlog/
> total 6.9G
> drwx------ 2 cassandra cassandra 12K 2011-06-24 20:38 .
> drwxr-xr-x 3 cassandra cassandra 4.0K 2011-06-25 01:47 ..
> -rw------- 1 cassandra cassandra 129M 2011-06-24 01:08
> CommitLog-1308876643288.log
> -rw------- 1 cassandra cassandra 28 2011-06-24 20:47
> CommitLog-1308876643288.log.header
> -rw-r--r-- 1 cassandra cassandra 129M 2011-06-24 01:36
> CommitLog-1308877711517.log
> -rw-r--r-- 1 cassandra cassandra 28 2011-06-24 20:47
> CommitLog-1308877711517.log.header
> -rw-r--r-- 1 cassandra cassandra 129M 2011-06-24 02:20
> CommitLog-1308879395824.log
> -rw-r--r-- 1 cassandra cassandra 28 2011-06-24 20:47
> CommitLog-1308879395824.log.header
> ...
> -rw-r--r-- 1 cassandra cassandra 129M 2011-06-24 20:38
> CommitLog-1308946745380.log
> -rw-r--r-- 1 cassandra cassandra 36 2011-06-24 20:47
> CommitLog-1308946745380.log.header
> -rw-r--r-- 1 cassandra cassandra 112M 2011-06-24 20:54
> CommitLog-1308947888397.log
> -rw-r--r-- 1 cassandra cassandra 44 2011-06-24 20:47
> CommitLog-1308947888397.log.header
> {noformat}
> The user KS has 2 CF's with 60 minute flush times. System KS had the default
> settings which is 24 hours. Will create another ticket see if these can be
> reduced or if it's something users should do, in this case it would not have
> mattered.
> I grabbed the log headers and used the tool in CASSANDRA-2828 and most of the
> segments had the system CF's marked as dirty.
> {noformat}
> $ bin/logtool dirty /tmp/logs/commitlog/
> Not connected to a server, Keyspace and Column Family names are not available.
> /tmp/logs/commitlog/CommitLog-1308876643288.log.header
> Keyspace Unknown:
> Cf id 0: 444
> /tmp/logs/commitlog/CommitLog-1308877711517.log.header
> Keyspace Unknown:
> Cf id 1: 68848763
> ...
> /tmp/logs/commitlog/CommitLog-1308944451460.log.header
> Keyspace Unknown:
> Cf id 1: 61074
> /tmp/logs/commitlog/CommitLog-1308945597471.log.header
> Keyspace Unknown:
> Cf id 1000: 43175492
> Cf id 1: 108483
> /tmp/logs/commitlog/CommitLog-1308946745380.log.header
> Keyspace Unknown:
> Cf id 1000: 239223
> Cf id 1: 172211
> /tmp/logs/commitlog/CommitLog-1308947888397.log.header
> Keyspace Unknown:
> Cf id 1001: 57595560
> Cf id 1: 816960
> Cf id 1000: 0
> {noformat}
> CF 0 is the Status / LocationInfo CF and 1 is the HintedHandof CF. I dont
> have it now, but IIRC CFStats showed the LocationInfo CF with dirty ops.
> I was able to repo a case where flushing the CF's did not mark the log
> segments as obsolete (attached unit-test patch). Steps are:
> 1. Write to cf1 and flush.
> 2. Current log segment is marked as dirty at the CL position when the flush
> started, CommitLog.discardCompletedSegmentsInternal()
> 3. Do not write to cf1 again.
> 4. Roll the log, my test does this manually.
> 5. Write to CF2 and flush.
> 6. Only CF2 is flushed because it is the only dirty CF.
> cfs.maybeSwitchMemtable() is not called for cf1 and so log segment 1 is still
> marked as dirty from cf1.
> Step 5 is not essential, just matched what I thought was happening. I thought
> SystemTable.updateToken() was called which does not flush, and this was the
> last thing that happened.
> The expired memtable thread created by Table uses the same cfs.forceFlush()
> which is a no-op if the cf or it's secondary indexes are clean.
>
> I think the same problem would exist in 0.8.
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