Showing posts with label read. Show all posts
Showing posts with label read. Show all posts

Sunday, July 3, 2016

apache cassandra 1.0.8 on READ_STAGE threads reference on sstables and so compaction cannot remove the sstables.

Back then when I was administer a apache cassandra 1.0.8 cluster, I noticed there were some (very little) sstables did not get remove even after compaction is done. The leftover sstables cause some administrative problem and I suspect could be due to maybe during reading of the sstables, this maybe not get remove.  
   private void replace(Collection<SSTableReader> oldSSTables, Iterable<SSTableReader> replacements)  
     View currentView, newView;  
       currentView = view.get();  
       newView = currentView.replace(oldSSTables, replacements);  
     while (!view.compareAndSet(currentView, newView));  

I supposed during replacement of the view and sstables, everything is atomic and hence during read, it will get from the new sstables. But I don't have enough high level knowledge on various subsystems work in cassandra. If you have an idea, please do leave your comment below.

This problem seem to go away after we upgraded the cluster to 1.1. I know by now (april 2016), cassandra 1.0, 1.1 or even 1.2 is ancient but if you are on 1.0 and pre1.0, you should really start to use cassandra 3.x or at least 2.x.