As I understand it, when you write to Cassandra, you are assured that, if successful, the new data has been written to a log file - so that if there is a crash your data is safe. Is this correct?

If the above is correct, there is something going on that I don't understand. Are the log files to which the data is first written the ones that look like /var/lib/cassandra/commitlog/CommitLog-1277998453387.log ? The reason I ask is that when I write a lot of data, nothing seems to change in the commitlog directory for a long time, then at some point the log files in this directory get updated. It looks to me like there's memory caching involved, and the new data is not being immediately written to disk. What is going on?