Entire list should not be blocked for updates during purge

During purge, we set the 'readRange' from start to end. As the purger iterates through the list, we don't shorten the 'readRange' by incrementing the starting point. This causes update() to mark the item stale and append the new item value to the end of the list. Due to this, if there are updates during the purge there can be increase in the number of stale items