Expert Oracle Exadata - Parent Directory

CHAPTER 13 MIGRATING TO EXADATA Note: When creating the database link, you can specify the database link’s TNS connect string directly, with aUSING clause, like this:CREATE DATABASE LINK ... USING '(DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HO/ST =localhost)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = ORA10G)))'That way, you don’t have to set up tnsnames.ora entries in the database server.Another option is to use INSERT SELECT for loading data into an existing table structure. We want tobypass the buffer cache, and the undo-generation-and-redo-logging mechanism for this bulk data load,so we can use the APPEND hint to make this a direct path load insert:INSERT /*+ APPEND */ INTO fact SELECT * FROM fact@sourcedb;COMMIT;We’re assuming here that the database is in NOARCHIVELOG mode during the migration, so we haven’tset any logging attributes for the table being loaded. In NOARCHIVELOG mode all bulk operations (such asINSERT APPEND, index REBUILD and ALTER TABLE MOVE) are automatically NOLOGGING.If your database must be in ARCHIVELOG mode during such data loading, but you still want to performthe loading of some tables without logging, then you can just temporarily turn off logging for thosetables for the duration of the load:ALTER TABLE fact NOLOGGING;INSERT /*+ APPEND */ INTO fact SELECT * FROM fact@sourcedb;ALTER TABLE fact LOGGING;Of course if your database or tablespace containing this table is marked FORCE LOGGING, then loggingwill still occur, despite any table-level NOLOGGING attributes.Achieving High-Throughput CTAS or IAS over a Database LinkWhile the previous examples are simple, they may not give you the expected throughput, especiallywhen the source database server isn’t in the same LAN as the target. The database links and theunderlying TCP protocol must be tuned for high throughput data transfer. The data transfer speed islimited obviously by your networking equipment throughput and is also dependent on the networkround-trip time (RTT) between the source and target database.When moving tens of terabytes of data in a short time, you obviously need a lot of networkthroughput capacity. You must have such capacity from end to end, from your source database to thetarget Exadata cluster. This means that your source server must be able to send data as fast as yourExadata cluster has to receive it, and any networking equipment (switches, routers) in between mustalso be able to handle that, in addition to all other traffic that has to flow through them. Dealing withcorporate network topology and network hardware configuration is a very wide topic and out of the429