On 2/2/2016 5:34 PM, Benjamin Smith wrote: > I'd like to know what the cause of a particular DB server's slowdown might be. > We've ruled out IOPs for the disks (~ 20%) and raw CPU load (top shows perhaps > 1/2 of cores busy, but the system slows to a crawl. > > We're suspecting that we're simply running out of memory bandwidth but have no > way to confirm this suspicion. Is there a way to test for this? Think: iostat > but for memory bandwidth instead of disk IO. memory bandwidth would show up as CPU busy, there's no distinction. 50% of your cores 100% busy, how many cores and how many waiting database tasks are there? typically with most database servers, one user connection == one core at a time. so if you have 16 cores, and only 8 busy/active database connections, that will tie up those 8 cores and leave the other 8 free. now the 8 processes will probably get bounced around between the cores, so it could end up looking like all 16 cores are 50% busy averaged over some sample rate, but thats the same net difference.. -- john r pierce, recycling bits in santa cruz