Re: Performances issues with SSD volume ?

Thomas SIMON <tsimon@xxxxxxxxxxx> · Mon, 18 May 2015 16:17:38 +0200



    Wow, thanks a lot for advice Koray! 

      This is a huge difference indeed !

      I will start with upgrading my kernel asap :) 

      Thomas
      Le 18/05/2015 15:51, Koray Eyidoğan a écrit :

    
      Hi Thomas,
        

        3.2 kernel may be #1 cause of your I/O load problem:
        

        http://www.databasesoup.com/2014/09/why-you-need-to-avoid-linux-kernel-32.html

        
        https://medium.com/postgresql-talk/benchmarking-postgresql-with-different-linux-kernel-versions-on-ubuntu-lts-e61d57b70dd4

        
        Have a nice day.
        

        Koray
        

        On Mon, May 18, 2015 at 4:35 PM, Thomas
          SIMON <tsimon@xxxxxxxxxxx>
          wrote:

          
              Hi matheus,

                thanks for reply.

                
                Kernel is slightly different ; with a
                3.10.23-xxxx-std-ipv6-64 kernel (OVH kernel) on HDD
                server, and  3.2.65-1+deb7u1 kernel on SSD server.

                I'm using debian wheezy on both servers.

                
                I didn't changed the 2 parameters you talk about.

                
                Thanks,
                Thomas
                
                   Le 18/05/2015 15:13, Matheus de
                    Oliveira a écrit :

                  
                        On Mon, May 18, 2015 at
                          10:05 AM, Thomas SIMON <tsimon@xxxxxxxxxxx>
                          wrote:

                           After the
                            change, I had the following behavior, and I
                            don't understand why : everything seems to
                            work fine (load is ~6/7, when it was
                            previously ~25/30 on the HDD server), so the
                            SSD server is faster than the HDD one, and
                            my apps run faster too, but after some time
                            (can be 5 minutes or 2 hours), the load
                            average increases suddently (can reach 150
                            !) and does not decrease, so postgres and my
                            application are almost unusable. (even small
                            requests are in statement timeout)
                        
                        
                      Before we go mad, what is
                        the OS/kernel/distro that you are using? Did it
                        change from the previous one?

                        
                        If Linux, have you disabled
                        transparent_huge_pages and zone_reclaim_mode
                        (two known problematic Linux features)?

                      
                      Best regards,

                      
                      -- 

                        Matheus de Oliveira

                          Analista de Banco de Dados

                          Dextra Sistemas - MPS.Br nível F!

                          www.dextra.com.br/postgres