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This instance relocation uses a new featured dubbed Oracle Omotion.

This instance relocation uses a new featured dubbed Oracle Omotion.

This is a similar approach to instance relocation that was first introduced by Savantis Systems with their DB-Switch invention, an offshoot of the Database Area Network (DAN) approach.

Doc ID: 578524.1

Note: It is very important to use entire address string in order to configure dispatchers on RAC and host name used in it should be a VIP hostname, otherwise connection may suffer intermittent ORA-12545 errors. Refer metalink note <333159.1>

alter system set dispatchers='(address=(protocol=tcp)(host=node1-vip))(dispatchers=2)' scope=both   sid='racdb1';

Here’s a handy little query I made up the other day to quickly digest any of the segment statistics from the AWR and grab the top objects for the cluster, reporting on each instance.

Any time you see heavy concurrency problems during inserts on table data blocks there should always be one first place to look: space management. Since ancient versions of OPS it has been a well-known fact that freelists are the enemy of concurrency.

One obvious method of reducing pings between instances is to isolate the transactions that use a specific data set to a specific server in the RAC cluster.

Some of the good RAC practices, to put it quite frankly, waste disk and memory space to improve data sharing and dispersal characteristics.

An example of an efficient RAC object is one that is used by only a single instance at a time. To achieve this singularity of use, the rows-per-block (RPB) of the data object must be reduced.

The client load balancing feature enables clients to randomize connection requests among the listeners. Tnsnames Parameter: LOAD_BALANCE

The connect-time failover enables clients to connect to another listener if the initial connection to the first listener fails. The number of listener protocol addresses determines how many listeners are tried. Without connect-time failover, Oracle Net attempts a connection with only one listener. The default is on. Tnsnames Parameter: FAILOVER

The listener connection load balancing feature improves connection performance by balancing the number of active connections among multiple dispatchers and instances. In a single-instance environment, the listener selects the least loaded dispatcher to handle the incoming client requests. In an Oracle Real Application Clusters (RAC) environment, connection load balancing also has the capability to balance the number of active connections among multiple instances. 1. Least-loaded node 2. Least-loaded instance 3. Least-loaded dispatcher for that instance (in case of Shared server configuration)

Cons of ASSM: §         Slow for full-table scans: Several studies have shown that large-table full-table scans (FTS) will run longer with ASSM than standard bitmaps. ASSM FTS tablespaces are consistently slower than freelist FTS operations. This implies that ASSM may not be appropriate for decision support systems and warehouse applications unless partitioning is used with Oracle Parallel Query. §        Slower for high-volume concurrent inserts: Numerous experts have conducted studies that show that tables with high volume bulk loads perform faster with traditional multiple freelists. §         ASSM will influence index clustering: For row ordered tables, ASSM can adversely affect the clustering_factor for indexes. Bitmap freelists are less likely to place adjacent tows on physically adjacent data blocks, and this can lower the clustering_factor and the cost-based optimizer's propensity to favor an index range scan.

Pros of ASSM: §          Varying row sizes: ASSM is better than a static pctused. The bitmaps make ASSM tablespaces better at handling rows with wide variations in row length. §         Reducing buffer busy waits: ASSM will remove buffer busy waits better than using multiple freelists. When a table has multiple freelists, all purges must be parallelized to reload the freelists evenly, and ASSM has no such limitation. §         Great for Real Application Clusters: The bitmap freelists remove the need to define multiple freelists groups for RAC and provide overall improved freelist management over traditional freelists.

Cons of ASSM: §         Slow for full-table scans: Several studies have shown that large-table full-table scans (FTS) will run longer with ASSM than standard bitmaps. ASSM FTS tablespaces are consistently slower than freelist FTS operations. This implies that ASSM may not be appropriate for decision support systems and warehouse applications unless partitioning is used with Oracle Parallel Query. §          Slower for high-volume concurrent inserts: Numerous experts have conducted studies that show that tables with high volume bulk loads perform faster with traditional multiple freelists. §          ASSM will influence index clustering: For row ordered tables, ASSM can adversely affect the clustering_factor for indexes. Bitmap freelists are less likely to place adjacent tows on physically adjacent data blocks, and this can lower the clustering_factor and the cost-based optimizer's propensity to favor an index range scan.