PLSQL Coding Standards and Best Practices

11.2 PLSQL New Feature : How to use DBMS_PARALLEL_EXECUTE to Update Large Tables in Parallel

The DBMS_PARALLEL_EXECUTE package enables you to incrementally update the data in a large table in parallel, in two high-level steps: 1. Group sets of rows in the table into smaller chunks. 2. Apply the desired UPDATE statement to the chunks in parallel, committing each time you have finished processing a chunk. This technique is recommended whenever you are updating a lot of data. Its advantages are: o You lock only one set of rows at a time, for a relatively short time, instead of locking the entire table. o You do not lose work that has been done if something fails before the entire operation finishes. o You reduce rollback space consumption. o You improve performance Different Ways to Spilt Workload : 1. CREATE_CHUNKS_BY_NUMBER_COL: Chunks the table associated with the given task by the specified column. 2. CREATE_CHUNKS_BY_ROWID : Chunks the table associated with the given task by ROWID 3. CREATE_CHUNKS_BY_SQL : Chunks the table associated with the given task by me...

Check Whether File Exists on the Server Using PLSQL

There are different packages using which you can check whether a file exists on the database / application server. The different ways are 1. Using UTL_HTTP from Web Server 2. Using UTL_FILE from Database Server 3. Using DBMS_LOB from Database Server 1. You can also use UTL_HTTP package to check whether a file exists on a web server from the database. SET SERVEROUTPUT ON DECLARE url VARCHAR2(256) := 'http://www.oracle.com/index1.html'; username VARCHAR2(256); password VARCHAR2(256); req UTL_HTTP.REQ; resp UTL_HTTP.RESP; BEGIN req := UTL_HTTP.BEGIN_REQUEST(url); IF (username IS NOT NULL) THEN UTL_HTTP.SET_AUTHENTICATION(req, username, password); END IF; resp := UTL_HTTP.GET_RESPONSE(req); DBMS_OUTPUT.PUT_LINE('response -->' || resp.status_code); END; / If the f...

PRAGMA AUTONOMOUS_TRANSACTION with Transaction Isolation

What is PRAGMA ? PRAGMA is a language construct that specifies how a compiler (or assembler or interpreter) should process its input. PRAGMA keyword in PLSQL is used to direct compiler to work differently when compared to the normal code. Pragmas are processed at compile time, not at run time. What is AUTONOMOUS_TRANSACTION ? The AUTONOMOUS_TRANSACTION pragma changes the way a subprogram works within a transaction. A subprogram marked with this pragma can do SQL operations and commit or roll back those operations, without committing or rolling back the data in the main transaction. The statement clearly states that autonomous transaction executes independent of main transaction. The concept was crystal clear to me and I had used it extensively in designing some of the solution. Very recently a question raised in my mind. Will the changes made by autonomous transaction be visible in the main transaction ? I didn't have an answer and hence tried to do a research. L...

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