Re: postgresql.conf recommendations

This looks like a problem of dirty memory being flushed to the disk. You should set your monitoring to monitor dirty memory from /proc/meminfo and check if it has any correlation with the slowdowns. Also vm.dirty_background_bytes should always be a fraction of vm.dirty_bytes, since when there is more than vm.dirty_bytes bytes dirty it will stop all writing to the disk until it flushes everything, while when it reaches the vm.dirty_background_bytes it will slowly start flushing those pages to the disk. As far as I remember vm.dirty_bytes should be configured to be a little less than the cache size of your RAID controller, while vm.dirty_background_bytes should be 4 times smaller.