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  1. Derby
  2. DERBY-3192

Cache session data in the client driver


    • Bug behavior facts:


      The reason for doing this is to avoid a rather
      substantial performance hit observed when the client driver is used
      together with an appserver that uses connection pooling. There are two

      1) The connection pool will compare the isolation level it has
      stored for the connection with the value returned from
      Connection.getTransactionIsolation() each and every time someone
      requests a new connection from the pool.

      2) The users of the connection pool (ab)use it to avoid having to keep
      track of their current connection. So each time a query needs to be
      executed a call to the connection pool's getConnection() method is
      made. Getting a connection from the connection pool like this also
      means that a new PreparedStatement must be prepared each time.

      The net result is that each query results in the following sequence:

      getTransactionIsolation() --> roundtrip + lookup in server's statement cache

      prepareStatment() --> roundtrip + lookup in server's statement cache

      executeQuery() --> roundtrip

      Arguably this is a "user error" but when suggesting this I'm kindly
      informed that this works "just fine" with other datbases (such as
      PostgreSQL and ORACLE).

      The reason why it works is that these databases do statement caching
      in the driver. I've tried to implement a very (too) simple statement
      cache in Derby's client driver and to re-enable caching of the
      isolation level (see
      https://issues.apache.org/jira/browse/DERBY-1148). With these changes
      I observe a marked performance improvement when running with appserver

      A proper statment cache cannot be implemented without knowing what the
      current schema is. If the current schema has changed since the
      statement was prepared, it is no longer valid and must be evicted from
      the cache.

      The problem with caching both the isolation level and the current schema in
      the driver is that both can change on the server without the client
      detecting it (through SQL and XA and possibly stored procedures).

      I think this problem can be overcome if we piggy-back the information we would
      like to cache on messages going back to the client. This can be done by
      utilizing the EXCSQLSET DRDA command. According to the DRDA spec (v4, volume 3,
      page 359-360) it is possible to add one or more SQLSTT objects after SQLCARD in the reply,

      I think it would be possible to cache additional session information when this becomes relevant. It
      would also be possible to use EXCSQLSET to batch session state changes
      going from the client to the server.


        1. derby-3192-test.v1.stat
          0.3 kB
          Dyre Tjeldvoll
        2. derby-3192-test.v1.diff
          31 kB
          Dyre Tjeldvoll
        3. derby-3192-test.fup2.diff
          10 kB
          Dyre Tjeldvoll
        4. derby-3192-test.fup1.diff
          10 kB
          Dyre Tjeldvoll
        5. derby-3192-mark2.v8.diff
          46 kB
          Dyre Tjeldvoll
        6. derby-3192-mark2.v7.diff
          46 kB
          Dyre Tjeldvoll
        7. derby-3192-mark2.v6.diff
          45 kB
          Dyre Tjeldvoll
        8. derby-3192-mark2.v5.diff
          45 kB
          Dyre Tjeldvoll
        9. derby-3192-mark2.v4.diff
          45 kB
          Dyre Tjeldvoll
        10. derby-3192-mark2.v3.diff
          43 kB
          Dyre Tjeldvoll
        11. derby-3192-mark2.v2.diff
          44 kB
          Dyre Tjeldvoll
        12. derby-3192-mark2.v1.diff
          43 kB
          Dyre Tjeldvoll
        13. derby-3192-fup.v1.diff
          2 kB
          Dyre Tjeldvoll
        14. derby-3192.prelim1.diff
          83 kB
          Dyre Tjeldvoll

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              • Assignee:
                dyret Dyre Tjeldvoll
                dyret Dyre Tjeldvoll
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