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FIRST_ROWS Hint → Description of the illustration first_rows_hint.gif The FIRST_ROWS hint instructs Oracle to … /*+ FIRST_ROWS(10) */ employee_id, last_name, salary, job_id FROM employees WHERE department_id = 20 … Hint" for additional information on the FIRST_ROWS hint and statistics
7.2.2 FIRST_ROWS(n) Mode → In FIRST_ROWS(n) mode, the optimizer in Oracle Database optimizes for fast response time by having … use the FIRST_ROWS(n) hint. If you want to optimize for better throughput under FIRST_ROWS(n), you … rows that satisfy the CONTAINS predicate are retrieved from the index: select /*+ FIRST_ROWS(10 … query optimizer
SDO_NN_DISTANCE Performance Improvement with FIRST_ROWS Hint → performance when you specify the FIRST_ROWS optimizer hint. For an example of using the FIRST_ROWS
7.1.2 Improved Response Time with FIRST_ROWS(n) Hint for ORDER BY Queries → FIRST_ROWS(n) hint. You use the FIRST_ROWS(n) hint in cases where you want the first number ( n ) of … cursor to retrieve the first 10 hits of a query and uses the FIRST_ROWS(n) hint to optimize the response … time: declare cursor c is select /*+ FIRST_ROWS(10) */ article_id from articles_tab where contains
ALL_ROWS Hint → employee_id = 107; If you specify either the ALL_ROWS or the FIRST_ROWS hint in a SQL statement, and if … FIRST_ROWS hint, then the optimizer gives precedence to the access paths and join operations specified by the hints.
Table 3-21 Hints by Functional Category → Hint Link to Syntax and Semantics Optimization Goals and Approaches ALL_ROWS Hint FIRST_ROWS Hint
Optimizer Hints → AUTOTRACE output in Example 7-4. Example 7-4 Execution Plan for SELECT with FIRST_ROWS Hint SELECT … /*+ FIRST_ROWS(25) */ employee_id, department_id FROM hr.employees WHERE department_id > 50
OPTIMIZER_MODE → | 1000] | first_rows | all_rows } Default value all_rows Modifiable ALTER SESSION, ALTER SYSTEM … time to return the first n rows (where n = 1, 10, 100, 1000). first_rows The optimizer uses a mix
Use of the Optimizer → as possible. Initial response time The FIRST_ROWS hint instructs the optimizer to get the first row
19.1 Overview of Optimizer Hints → : SELECT /*+ FIRST_ROWS(10) */ * FROM employees; See Also: Oracle Database SQL Language Reference to a complete list of hints supported by Oracle Database
21.6.2 Sample TKPROF Body → 0.00 0 0 0 0 Misses in library cache during parse: 1 Optimizer mode: FIRST_ROWS Parsing user id: 44 … ------- ------ -------- ---------- ---------- ---------- ---------- ---------- total 4 0.02 0.01 0 15 0 1 Misses in library cache during parse: 1 Optimizer mode: FIRST_ROWS
11.5.2 Choosing an Optimizer Goal → 1, 10, 100, or 1000. FIRST_ROWS The optimizer uses a mix of cost and heuristics to find a best plan … the heuristic. FIRST_ROWS is available for backward compatibility and plan stability; use
Table 11-5 Hints for Changing the Query Optimizer Goal → Hint Description FIRST_ROWS( n ) This hint instructs Oracle Database to optimize an individual SQL
7.7.9 How do I make an ORDER BY score query faster? → Answer: Sorting by relevance ( SCORE(n) ) can be extremely quick if the FIRST_ROWS(n) hint is used … tables. An example of such a query: SELECT /*+ FIRST_ROWS(10) */ ID, SCORE(1), TEXT FROM mytable WHERE
Initialization Parameters for Query Rewrite → : OPTIMIZER_MODE = ALL_ROWS (default), FIRST_ROWS, or FIRST_ROWS_ n With OPTIMIZER_MODE set to FIRST_ROWS, the
Contents → DYNAMIC_SAMPLING Hint FACT Hint FIRST_ROWS Hint FULL Hint HASH Hint IGNORE_ROW_ON_DUPKEY_INDEX Hint INDEX
How Oracle Database Processes DML → * FROM my_table; ALTER SESSION SET OPTIMIZER_MODE=FIRST_ROWS; SELECT * FROM my_table; ALTER SESSION SET
Ensuring that Query Rewrite Takes Effect → OPTIMIZER_MODE to ALL_ROWS, FIRST_ROWS, or FIRST_ROWS_ n. If step 1 has not been completed, a
19.1.2 Hints by Category → ALL_ROWS and FIRST_ROWS( n ) hints let you choose between optimization approaches and goals. If a SQL … not affect SQL run within PL/SQL. If you specify either the ALL_ROWS or the FIRST_ROWS ( n ) hint … you specify hints for access paths or join operations along with either the ALL_ROWS or FIRST_ROWS