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From "Ching-cheng (JIRA)" <>
Subject [jira] Created: (CASSANDRA-2183) memtable_flush_after_mins setting not working
Date Thu, 17 Feb 2011 16:52:24 GMT
memtable_flush_after_mins setting not working

                 Key: CASSANDRA-2183
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 0.7.1, 0.7.0
            Reporter: Ching-cheng
            Priority: Minor

We have observed the behavior that memtable_flush_after_mins setting not working occasionally.
  After some testing and code digging, we finally figured out what going on.
The memtable_flush_after_mins won't work on certain condition with current implementation
in Cassandra.

In org.apache.cassandra.db.Table,  the scheduled flush task is setup by the following code
during construction.

int minCheckMs = Integer.MAX_VALUE;
for (ColumnFamilyStore cfs : columnFamilyStores.values())  
    minCheckMs = Math.min(minCheckMs, cfs.getMemtableFlushAfterMins() * 60 * 1000);

Runnable runnable = new Runnable()
   public void run()
       for (ColumnFamilyStore cfs : columnFamilyStores.values())
flushTask = StorageService.scheduledTasks.scheduleWithFixedDelay(runnable, minCheckMs, minCheckMs,

Now for our application, we will create a keyspacewithout any columnfamily first.  And only
add needed columnfamily later depends on request.

However, when keyspacegot created (without any columnfamily ), the above code will actually
schedule a fixed delay flush check task with Integer.MAX_VALUE ms
since there is no columnfamily yet.

Later when you add columnfamily to this empty keyspace, the initCf() method in
doesn't check whether the scheduled flush check task interval need
to be updated or not.   To fix this, we'd need to restart the Cassandra after columnfamily
added into the keyspace. 

I would suggest that add additional logic in initCf() method to recreate a scheduled flush
check task if needed.

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