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Enabling Distributed Transactions

Enabling Distributed Transactions. Objectives. After completing this lesson, you should be able to: Verify network configuration Explain the differences between remote transactions and distributed transactions Establishing communication between databases through database links. sqlnet.ora.

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Enabling Distributed Transactions

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  1. Enabling Distributed Transactions

  2. Objectives • After completing this lesson, you should be able to: • Verify network configuration • Explain the differences between remote transactions and distributed transactions • Establishing communication between databases through database links

  3. sqlnet.ora tnsnames.ora listener.ora Oracle Net Services Review Application Oracle Net RDBMS Oracle Net Listener TCP/IP network Client Database server

  4. Connecting to an Oracle Database finance.us.flowers.com Database server

  5. finance.us.flowers.com Client Application Connectivity to the Oracle Server flowers-server Oracle Database Network Connection sqlplus hr/hr@FINANCE

  6. Detroit Pittsburgh Server-Server Connectivity CREATE DATABASE LINKfin_flowers CONNECT TO hr IDENTIFIED BY hr USING 'FINANCE'; SELECT * FROMemployees@fin_flowers; Oracle Net Physical Network Link Oracle Net

  7. Types of Database Links • Database links have three dimensions: • Global, public, and private • Fixed user, connected user, current user • Shared or nonshared

  8. Creating Database Links 3 2 1

  9. Creating Database Links • Create a private link that uses the net service name ‘PGH_SALES’: • Create a public database link for the database service ORCL: • Use the private database link in a query: CREATE DATABASE LINK hq.sales.acme.com CONNECT TO hr IDENTIFIED BY hr USING 'pgh_sales'; CREATE PUBLIC DATABASE LINK orcl USING 'ORCL'; SELECT * FROM hr.employees@hq.sales.acme.com;

  10. Dropping Links • Drop a link when the application no longer uses it • Redefine a link when: • Security breaches demand it • Physical databases must be moved • Network protocols change • Node names change DROP [PUBLIC] DATABASE LINK linkname;

  11. Data Dictionary Views • DBA_DB_LINKS • USER_DB_LINKS • ALL_DB_LINKS • V$DBLINK

  12. Remote Query • The user is connected to a local database and a database link is used to query data from a single remote database. • The local database sends the entire query to the remote database to be processed.

  13. Detroit Pittsburgh Executing a Remote Query SELECT * FROMemployees@fin_flowers; Oracle Net Physical Network Link Oracle Net

  14. Distributed Query • The user is connected to a local database and issues a query involving tables from at least two databases. • The query is always executed from a local database. • The local database decomposes the query into subqueries to be sent to each remote database. • The local database retrieves data from remote databases and performs any necessary post-processing.

  15. Detroit Toronto Pittsburgh Executing a Distributed Query SELECT e.last_name,j.job_title FROM employees@pittsburgh e, jobs@detroit j, job_history hWHERE e.job_id = j.job_id AND e.employee_id = h.employee_id AND h.end_date >= SYSDATE-30; Local database SELECT employee_id, end_date FROM job_history; SELECT last_name, job_id FROM employees; SELECT job_id, job_title FROM jobs;

  16. Distributed and Remote Transactions INSERT INTO jobs@detroit VALUES ('CEO','Chief Executive Officer',18000,34000); UPDATE employees@pittsburgh SET job_id = 'CEO' WHERE last_name = 'Hart'; COMMIT;

  17. Detroit Toronto Pittsburgh In-Doubt Transactions 1. UPDATE jobs@detroit... 2. UPDATE job_history@toronto... 3. Toronto database becomes unavailable. 4. Commit fails UPDATE jobs@detroit...; UPDATE job_history@toronto...; COMMIT; Local Database

  18. Summary • In this lesson, you should have learned about: • Client-server and server-server architectures • Network configuration files and processes • Differences between remote queries and distributed queries • Establishing communication between databases through database links

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