Before jumping into my proposed solution, let me just make a quick note about what's stored on the journal. // A list of dataFiles (used files) private final Queue dataFiles; //A list of freeFiles private final Queue freeFiles = new ConcurrentLinkedQueue(); //A list of freeFiles but already opened (for fast move forward on the journal) private final BlockingQueue openedFiles; //A list of Adds and updates for each recordID // This is being renamed to recordsMap BTW private final ConcurrentMap<Long, PosFiles> posFilesMap; now the compacting would be: Startup exclusiveLockOnJournal (for a very short time, this is required to take a valid snapshot before compacting starts) { - Disallow reclaiming while compacting is being done - set some flag such as compacting = true - Take a snapshot of dataFiles, posFilesMap and pending transactions. - I believe } - for each dataFile on the snapshot - append valid records (based on the snapshot) to a new temporary datafile. if the temporary datafile is full, open a new one - as records are appended, calculate the new posFilesMap - As soon as the compacting is done, I need to rename temporary files (using the process you originaly described.. with a small mark file) - I need also to update the posfilesMap. I will take the list of updates and deletes tha happened while compacting was working, and replay them on the new posfilesMap (in a fast operation). This is because at this point, I wouldn't have any information about deletes and updates. - When a delete happen, you only have a neg added to DataFile, and I wouldn't know how to replay the information. - For updates, I only have a list of what files took an update (inside PosFiles). You could have two updates on a same file, and each updates was sent to a different file So far I need to compute that information, as I don't have it anywhere. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4240085#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...