16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
111 lines
2.3 KiB
Plaintext
111 lines
2.3 KiB
Plaintext
== Why is this an issue?
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The ``++FETCH ... INTO++`` statement is inefficient when used in a loop (where many records are expected). It leads to many context-switches between the SQL and PL/SQL engines. Instead, the ``++FETCH ... BULK COLLECT INTO++`` statement will issue the SQL requests in bulk, minimizing context switches.
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=== Noncompliant code example
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[source,sql]
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----
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SET SERVEROUTPUT ON
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CREATE TABLE largeTable AS SELECT ROWNUM AS id FROM all_objects;
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SET TIMING ON
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DECLARE
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x PLS_INTEGER;
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CURSOR largeCursor IS SELECT ROWNUM FROM largeTable;
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largeTableRowId BINARY_INTEGER;
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BEGIN
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OPEN largeCursor;
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x := 0;
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LOOP
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FETCH largeCursor INTO largeTableRowId; -- Noncompliant
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EXIT WHEN largeCursor%NOTFOUND;
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x := x + largeTableRowId;
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END LOOP;
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DBMS_OUTPUT.PUT_LINE('Sum of rownums using alternative 1: ' || x);
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CLOSE largeCursor;
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END;
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/
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SET TIMING OFF
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DECLARE
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r largeTable%ROWTYPE;
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CURSOR myCursor IS SELECT * FROM largeTable;
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BEGIN
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OPEN myCursor;
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FETCH myCursor INTO r; -- Compliant, outside of a loop
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CLOSE myCursor;
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END;
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/
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DROP TABLE largeTable;
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----
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=== Compliant solution
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[source,sql]
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----
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SET SERVEROUTPUT ON
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CREATE TABLE largeTable AS SELECT ROWNUM AS id FROM all_objects;
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SET TIMING ON
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DECLARE
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x PLS_INTEGER;
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CURSOR largeCursor IS SELECT * FROM largeTable;
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TYPE largeTableRowIdArrayType IS TABLE OF BINARY_INTEGER INDEX BY BINARY_INTEGER;
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largeTableRowIdArray largeTableRowIdArrayType;
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BEGIN
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OPEN largeCursor;
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x := 0;
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LOOP
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FETCH largeCursor BULK COLLECT INTO largeTableRowIdArray LIMIT 1000; -- Compliant
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FOR i IN largeTableRowIdArray.FIRST .. largeTableRowIdArray.LAST LOOP
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x := x + largeTableRowIdArray(i);
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END LOOP;
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EXIT WHEN largeCursor%NOTFOUND;
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END LOOP;
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DBMS_OUTPUT.PUT_LINE('Sum of rownums using alternative 2: ' || x);
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CLOSE largeCursor;
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END;
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/
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SET TIMING OFF
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DECLARE
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r largeTable%ROWTYPE;
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CURSOR myCursor IS SELECT * FROM largeTable;
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BEGIN
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OPEN myCursor;
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FETCH myCursor INTO r; -- Compliant, outside of a loop
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CLOSE myCursor;
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END;
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/
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DROP TABLE largeTable;
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Replace this use of "FETCH ... INTO" with "FETCH ... BULK COLLECT INTO".
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endif::env-github,rspecator-view[]
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