Hi, thanks everyone here for show your idea and thinking here. Finally I am sure the two sessions shown on two instances are because I queried gv$view, and gv$view will spawn parallel session on different instances to return the information on each nodes, so that's why I saw there is one session for each nodes. Thanks Nilo Segura, Your inforamtion is very useful to learn RAC. Thanks, Qihua On 9/27/07, qihua wu <staywithpin@xxxxxxxxx> wrote: > > Hi, Nilo, thanks for your reply. But I didn't configure the method > parameter. > test = > (DESCRIPTION = > (SDU = 32768) > (enable = broken) > (LOAD_BALANCE = yes) > (ADDRESS = > (PROTOCOL = TCP) > (HOST = server1) > (PORT = 1525) > ) > (ADDRESS = > (PROTOCOL = TCP) > (HOST = server2) > (PORT = 1525) > ) > (CONNECT_DATA = > (SERVICE_NAME = test) > ) > ) > > This time I query again against gv$mystat. It shows two different sid now. > When I queried it this morning, the number of the two sid were the same. > SQL> select unique sid from gv$mystat; > > SID > ---------- > 542 > 550 > > On 9/27/07, Nilo Segura <nilosegura@xxxxxxxxx> wrote: > > > > No, there is an option such that the client will connec to both > > instance(s) at the same time. In the normal case, you are connected to one > > instance, then will failover to the other instance(s). It is what Andrew > > Kerber mentioned in his post.. > > > > Check the connect string being used. The keywork to look for is > > FAILOVER_MODE ... here is a snipet of the oracle doc. See the > > METHOD -> PRECONNECT... > > > > This can explain what you see.. > > > > FAILOVER_MODE Subparameter Description > > > > BACKUP > > > > Specify a different net service name for backup connections. A backup > > should be specified when using preconnect to pre-establish connections. > > > > TYPE > > > > Specify the type of failover. Three types of Oracle Net failover > > functionality are available by default to Oracle Call Interface (OCI) > > applications: > > > > - > > > > session: Set to failover the session. If a user's connection is > > lost, a new session is automatically created for the user on the backup. > > This type of failover does not attempt to recover selects. > > - > > > > select: Set to enable users with open cursors to continue fetching > > on them after failure. However, this mode involves overhead on the client > > side in normal select operations. > > - > > > > none: This is the default. No failover functionality is used. This > > can also be explicitly specified to prevent failover from happening. > > > > METHOD > > > > Determines how fast failover occurs from the primary node to the backup > > node: > > > > - > > > > basic: Set to establish connections at failover time. This option > > requires almost no work on the backup server until failover time. > > - > > > > preconnect: Set to pre-established connections. This provides > > faster failover but requires that the backup instance be able to support > > all > > connections from every supported instance. > > > > RETRIES > > > > Specify the number of times to attempt to connect after a failover. If > > DELAY is specified, RETRIES defaults to five retry attempts. > > > > Note: If a callback function is registered, then this subparameter is > > ignored. > > > > DELAY > > > > Specify the amount of time in seconds to wait between connect attempts. > > If RETRIES is specified, DELAY defaults to one second. > > > > Note: If a callback function is registered, then this subparameter is > > ignored. > > > > > > > > > -- > > > > > Nilo Segura > > > > > Oracle Support - IT/DES > > > > > CERN - Geneva > > > > > Switzerland > > > > > > > > >