This is because all hits to the query across all partitions must be obtained before the results can be sorted. This discussion is most applicable in an OLTP environment, where the access paths either to the parent SQL or subquery are through indexed columns with high selectivity. Avoid mixed-mode expressions, and beware of implicit type conversions. Answer: Yes. RETURNING to select and modify data with a single call. After you have identified the candidate SQL statements, the next stage is to gather information that enables you to examine the statements and tune them. The purpose of dynamic sampling is to improve server performance by determining more accurate selectivity and cardinality estimates. However, if 50 programmers each create an index, then application performance will probably be hampered. Also inside each partition, index creation is done in parallel (intra-partition parallelism) with a parallel degree of 2. In the first and most common case, the kernel asks the text index for all the rowids that satisfy a particular text search. UPDATE table1 SET table1.col1 = 'G' WHERE EXISTS (SELECT table2.col2 FROM table2 WHERE table1.col1 = table2.col1) and table1.col1 IS NULL Use of the FIRST_ROWS hint in conjunction with ORDER BY SCORE(n) DESC tells Oracle Text to accept a sorted set from the text index, and not to do a further sort. Subquery unnesting merges the body of the subquery into the body of the statement that contains it, allowing the optimizer to consider them together when evaluating access paths and joins. You use the PARALLEL keyword when creating the index: This will create the index with up to three separate indexing processes depending on your resources. Traces are associated with a session—they can measure operations that take place within a single session, and, conversely, cannot make measurements across sessions. CTXCAT indexes take a bit longer to create and use considerably more disk space than CONTEXT indexes. For BUFFER_GETS, divide each SQL statement's BUFFER_GETS by the total number of buffer gets during the period. Join order can have a significant effect on performance. "Index Optimization" in Chapter 3, " Indexing". However, this means that your data will become progressively more out of date, which may be unacceptable for your users. This is the default behavior. For querying, you are hoping to get as much information cached in the system global area's (SGA) block buffer cache as possible. Figure 6-1 is an illustration of SQL Analyze displaying the SQL statement used in Example 1-3, "Using EXPLAIN PLAN". Answer: The fastest type of query will meet the following conditions: Only the first page of results is returned (for example, the first 10 or 20 hits). This is the default behavior when you use the FIRST_ROWS hint. For indexed lookups, the $R table, DR$indexname$R, is used. Applications should try to access each row only once. You can maintain the existing execution plan of SQL statements over time either using stored statistics or stored SQL execution plans. The COUNT() function accepts a clause which can be either ALL, DISTINCT, or *:. To do so, you can issue any of the following statements: You can delete the statistics associated with a table by issuing: You can delete statistics on one index by issuing the following statement: By default, Oracle Text optimizes queries for throughput. If not, then do not use the view. This leads to three general rules: The following example shows how to tune join order effectively: The first three conditions in the previous example are filter conditions applying to only a single table each. Oracle Query Optimization Tool (The Query Optimizer), is a built-in database software which helps in the optimization of SQL queries in Oracle, by finding out the most efficient method in which a SQL query can access data from an Oracle database. Often, however, this is not the case. Create an unusable index first, then run the DBMS_PCLXUTIL.BUILD_PART_INDEX utility. When queries are optimized for throughput, Oracle Text returns all rows in the shortest time possible. You can also set your index memory at run time with the CREATE INDEX memory parameter in the parameter string. In order to use a query like this, we must copy all the data into a single text column for indexing, with section tags around each column's data. Oracle Forms and Reports are powerful development tools that allow application logic to be coded using PL/SQL (triggers or program units). Each number is calculated as one column. Collecting statistics on your tables enables Oracle Text to do cost-based analysis. In this case, Oracle Text performs a high speed internal sort when fetching from the text index tables. As a benchmark, with an average document size of 5K, Oracle Text can index approximately 200 documents per second with the following hardware and parallel configuration: XML news documents that averaged 5K in size. Because of this, Oracle recommends that you disable parallel querying after parallel indexing. Combining multiple scans into one scan can be done by moving the WHERE condition of each scan into a CASE statement, which filters the data for the aggregation. Answer: There are two ways the kernel can query the text index. You can work around this by using an inline view when you use the FIRST_ROWS hint. This results in queries returning all rows in shortest time possible. oracle 11gr2 on AIX Table1 contains 63 million. However, indexing performance only improves when you have multiple CPUs. Answer: There are generally two measures of query performance: response time, the time to get an answer to an individual query, and. The optimizer attempts to choose the best execution plan based on the following parameters: the selectivity on the CONTAINS predicate, the selectivity of other predicates in the query, the CPU and I/O costs of processing the CONTAINS predicates. The SQL statements in the TKPROF output file can be ordered by various parameters, such as the execution elapsed time (exeela), which usually assists in the identification by ordering the SQL statements by elapsed time (with highest elapsed time SQL statements at the top of the file). Even though parallel querying is the default behavior for indexes created in parallel, it usually results in degrading overall query throughput on heavily loaded systems. Before reusing a view, determine whether all tables in the view need to be accessed to return the data. 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