2 Replies Latest reply: Apr 17, 2012 11:02 AM by 603349 RSS

    Question regarding smart flash cache

    897831
      If my entire db is smaller than the amount of smart flash cache that is available, would Exadata automatically cache entire DB in smart flash cache?
      I understand I can tell Exadata to pin tables in cache but just curious to know if Exadata would do it on its own in this scenario.
      Thanks.
        • 1. Re: Question regarding smart flash cache
          tychos
          Hi,
          Based on the figures the answer is no.
          ..
          SQL> alter table flash_test STORAGE (CELL_FLASH_CACHE NONE);

          Table altered.

          Elapsed: 00:00:00.06
          SQL> select count(*) from flash_test;

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:11.18
          SQL> /

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:03.47
          SQL> /

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:03.17
          SQL> alter table flash_test STORAGE (CELL_FLASH_CACHE KEEP);

          Table altered.

          Elapsed: 00:00:00.02
          SQL> select count(*) from flash_test;

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:04.35
          SQL> /

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:01.63
          SQL> /

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:01.65
          SQL> alter table flash_test STORAGE (CELL_FLASH_CACHE NONE);

          Table altered.

          Elapsed: 00:00:00.06
          SQL> select count(*) from flash_test;

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:03.94
          SQL> /

          COUNT(*)
          ----------
          33554432

          Elapsed: 00:00:03.40
          ..
          Rgds,
          Tycho
          • 2. Re: Question regarding smart flash cache
            603349
            user12254641 wrote:
            If my entire db is smaller than the amount of smart flash cache that is available, would Exadata automatically cache entire DB in smart flash cache?
            No, it would not be cached simply because the DB is smaller in size than the Smart Flash Cache. Caching is done because of data access, so frequently accessed data will be cached. Data at the cold end of the LRU algorithm gets aged off and replaced.

            It's very similar to the DB buffer cache -- you don't expect all your data to be cached simply because the DB cache is bigger than your data. However, if the frequently accessed data can all be cached, it will.


            --
            Regards,
            Greg Rahn | blog | twitter | linkedin