8 Replies Latest reply: May 9, 2011 12:08 PM by 736543 RSS

    Virtual Memory PAging 11G

    user10191672
      Hi,

      we are currently working on OEL 5.6 with Oracle 11.2.0.2 and we facing the problem that ADDM reports "Significant virtual memory paging was detected on the host operating system". The server has 32 GB RAM. sga_max_size is 8 GB and sga_target 6G.

      On the host I used vmstat and sar to monitor system paging.
      vmstat 1 1000
       4  2      0 389976 2418116 24471108    0    0  1036  1025 15799 13209  2  4 90  4  0
       1  0      0 391604 2418116 24471104    0    0   448  2872 16691 15931  3  4 91  2  0
       3  0      0 386256 2418116 24471108    0    0   116  1293 16504 15177  3  4 93  0  0
       1  1      0 392440 2418116 24471112    0    0   572  1336 16248 13922  2  4 92  2  0
       3  0      0 391176 2418116 24471112    0    0   948  2345 16522 16901  3  4 90  3  0
       2  1      0 387472 2418116 24471112    0    0  2520  1291 15889 13184  3  4 86  6  0
       2  2      0 396532 2418116 24471140    0    0   972  1375 15476 13051  4  4 86  5  0
       2  0      0 395284 2418116 24471140    0    0   428  7153 15258 13561  3  5 91  2  0
       1  1      0 409808 2418116 24471140    0    0    88  1637 15245 12187  2  4 93  1  0
       1  1      0 409700 2418116 24471140    0    0   772  1154 13904 11563  2  3 92  3  0
       1  1      0 402624 2418116 24471140    0    0  1256  2034 14343 11919  2  4 90  4  0
      
      sar -B
      08:50:01     pgpgin/s pgpgout/s   fault/s  majflt/s
      09:00:01     13478,30   9531,89  25713,92      0,01
      09:10:01      7216,15   8411,93  20764,19      0,08
      09:20:01      8592,63   9439,34  25570,95      0,04
      09:30:01      7907,54  11233,99  26470,02      0,01
      09:40:01      9557,42  11173,01  24437,09      0,00
      09:50:01      7784,97  12488,09  27895,67      0,00
      10:00:01      6192,32  12312,82  23105,25      0,00
      10:10:01      5932,37  12533,04  24738,46      0,01
      10:20:01      5518,63  11526,15  27869,31      0,02
      10:30:01      6029,42  11289,92  28177,30      0,03
      10:40:01      9356,77  12094,89  25259,83      0,06
      10:50:01     11134,70  12639,44  26402,50      0,01
      11:00:01      6854,48  10705,63  28082,56      0,07
      11:10:01      7753,94  12355,98  30062,13      0,02
      11:20:01      5752,87   9254,05  35342,96      0,01
      11:30:01      6655,89   9389,43  33327,88      0,02
      11:40:01      3707,29   7019,89  27827,03      0,04
      11:50:01      4625,24   8150,20  24881,20      0,00
      12:00:01      5383,71   9572,60  27779,76      0,00
      12:10:01      3841,06   7310,87  24833,04      0,01
      12:20:01      5537,75   7376,26  27909,33      0,02
      12:30:01      7101,03   7826,72  21734,78      0,00
      12:40:01      4360,04   6875,13  19737,41      0,84
      free shows a lot of unused memory:
      free -m
                   total       used       free     shared    buffers     cached
      Mem:         32103      31874        229          0       2361      24107
      -/+ buffers/cache:       5405      26698
      Swap:        34047          0      34047
      For Oracle installation we used oraclevalidated.

      Why does ADDM report Virtual memory paging? Any help would be appreciated.
        • 1. Re: Virtual Memory PAging 11G
          SatishKandi
          What other processes are running on this server?
          Oracle need not be the only process responsible for paging.
          • 2. Re: Virtual Memory PAging 11G
            user10191672
            This server is exclusively for Oracle. top doesn't show any unusual processes.
            • 3. Re: Virtual Memory PAging 11G
              Fahd.Mirza
              Hi,
              You can check start with checking 3 things:

              1) Is the swap space enough for Oracle?
              2) As Satish said, identify which process at the OS level is consuming memory. Is it Oracle really? And if it is Oracle, then what session(s) is consuming memory and why?
              3) Check from OEM whether you have set the SGA size correctly. At the very superficial level, you have 32GB RAM and have just given max 8GB to Oracle. Why not give it more if it requires more? I presume you are using 64-bit infrastructure?

              regards
              • 4. Re: Virtual Memory PAging 11G
                user10191672
                Hi,

                thanks for your reply:

                1. There is more than enough swap space:
                free -m
                             total       used       free     shared    buffers     cached
                Mem:         32103      31805        297          0       2364      24375
                -/+ buffers/cache:       5065      27038
                Swap:        34047          0      34047
                2. top doesn't show any unusual processes. Just oracle is consuming a lot of memory.

                3. I don't accutally understand how more sga space should help here. Could you please clarify?

                I don't understand why the server pages at all. I know that some paging is normal. but that much? Linux has about 25 GB for caching. It could give some space away.
                • 5. Re: Virtual Memory PAging 11G
                  Fahd.Mirza
                  3. I don't accutally understand how more sga space should help here. Could you please clarify?
                  For SGA Advice check v$sga_target_advice or you can check same information from EM. It usually provides a very good advice.

                  regards
                  • 6. Re: Virtual Memory PAging 11G
                    wiZ
                    Increasing the SGA size would also increase paging.

                    I think the main reason for this is having too many pages. Please try to configure database with huge pages. See also note 361468.1.

                    HTH..

                    - wiZ
                    • 7. Re: Virtual Memory PAging 11G
                      user10191672
                      Thanks wiz.. I think that did the trick.
                      • 8. Re: Virtual Memory PAging 11G
                        736543
                        ADDM reports "Significant virtual memory paging was detected on the host operating system". The server has 32 GB RAM. sga_max_size is 8 GB and sga_target 6G.
                        I had such message when despite of sufficient SGA_TARGET there was incredibly small Buffer_Cache. Because of mistakenly set big db_cache_4k_size AMM shrunk default buffer cache to 20Mb :))
                        So you could look at your SGA buffers distribution and check Buffer_cache_hit_ratio

                        PS In that case there also was no paging in OS according to vmstat output.

                        Edited by: user12216579 on May 9, 2011 10:01 AM

                        Edited by: user12216579 on May 9, 2011 10:07 AM