Speeding up text queries with search optimization

Search optimization can improve the performance of queries that use the SEARCH and SEARCH_IP functions. These queries search for character data (text) and IPv4 addresses in specified columns from one or more tables, including fields in VARIANT, OBJECT, and ARRAY columns.

Note

You must enable this feature for specific columns using the ON clause in the ALTER TABLE … ADD SEARCH OPTIMIZATION command. For example:

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(play, character, line);
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Text searches are not optimized if you omit the ON clause.

The following sections provide more details:

Conditions for runtime use of FULL_TEXT search optimization

After you have enabled FULL_TEXT search optimization on a table that is queried with the SEARCH function, the search access path for the optimization can be used during query planning and execution. The following conditions must be met:

  • The search optimization must be ready for use (active column = TRUE in the DESCRIBE SEARCH OPTIMIZATION output).

  • The search optimization must be enabled on a superset of the columns specified in the SEARCH predicate. For example, if a table contains VARCHAR columns c1,c2,c3,c4,c5, the search optimization covers columns c1,c2,c3, and the function searches one, two, or three of those columns (but not c4 or c5), the query can benefit from FULL_TEXT search optimization.

  • The analyzer defined for the search optimization in the ALTER TABLE command must be the same as the analyzer specified in the SEARCH function call.

Tip

To find out if a specific search access path was used for a query, look for a Search Optimization Access node in the query profile.

Examples of ADD (and DROP) FULL_TEXT search optimization

The following examples show how to enable FULL_TEXT search optimization on columns in a table to improve query performance when the SEARCH function is used to query those columns.

Enable FULL_TEXT search optimization with a specific analyzer

The following example enables FULL_TEXT search optimization on one column and specifies an analyzer. The combination of optimization type and analyzer (method) is reflected in the DESCRIBE output.

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(line, ANALYZER => 'UNICODE_ANALYZER');
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DESCRIBE SEARCH OPTIMIZATION ON lines;
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+---------------+----------------------------+--------+------------------+--------+
| expression_id | method                     | target | target_data_type | active |
|---------------+----------------------------+--------+------------------+--------|
|             1 | FULL_TEXT UNICODE_ANALYZER | LINE   | VARCHAR(2000)    | true   |
+---------------+----------------------------+--------+------------------+--------+

If you enable FULL_TEXT search optimization on the same column with the default analyzer, the DESCRIBE output returns two rows and differentiates the two entries by expression ID and method.

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(line);
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DESCRIBE SEARCH OPTIMIZATION ON lines;
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+---------------+----------------------------+--------+------------------+--------+
| expression_id | method                     | target | target_data_type | active |
|---------------+----------------------------+--------+------------------+--------|
|             1 | FULL_TEXT UNICODE_ANALYZER | LINE   | VARCHAR(2000)    | true   |
|             2 | FULL_TEXT DEFAULT_ANALYZER | LINE   | VARCHAR(2000)    | false  |
+---------------+----------------------------+--------+------------------+--------+

Enable FULL_TEXT search optimization on a VARIANT column

The following command enables FULL_TEXT search optimization on a VARIANT column. (This car_sales table and its data are described under Querying Semi-structured Data.)

ALTER TABLE car_sales ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(src);

DESCRIBE SEARCH OPTIMIZATION ON car_sales;
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+---------------+----------------------------+--------+------------------+--------+
| expression_id | method                     | target | target_data_type | active |
|---------------+----------------------------+--------+------------------+--------|
|             1 | FULL_TEXT DEFAULT_ANALYZER | SRC    | VARIANT          | true   |
+---------------+----------------------------+--------+------------------+--------+

Drop FULL_TEXT optimization from one or more columns

You can enable FULL_TEXT optimization on multiple columns, then later drop the optimization from one or more of those columns. The remaining columns are still optimized.

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(play, act_scene_line, character, line, ANALYZER => 'UNICODE_ANALYZER');

DESCRIBE SEARCH OPTIMIZATION ON lines;
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+---------------+----------------------------+----------------+------------------+--------+
| expression_id | method                     | target         | target_data_type | active |
|---------------+----------------------------+----------------+------------------+--------|
|             1 | FULL_TEXT UNICODE_ANALYZER | PLAY           | VARCHAR(50)      | true   |
|             2 | FULL_TEXT UNICODE_ANALYZER | ACT_SCENE_LINE | VARCHAR(10)      | true   |
|             3 | FULL_TEXT UNICODE_ANALYZER | CHARACTER      | VARCHAR(30)      | true   |
|             4 | FULL_TEXT UNICODE_ANALYZER | LINE           | VARCHAR(2000)    | true   |
+---------------+----------------------------+----------------+------------------+--------+

ALTER TABLE lines DROP SEARCH OPTIMIZATION ON 1, 2, 3;
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DESCRIBE SEARCH OPTIMIZATION ON lines;
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+---------------+----------------------------+--------+------------------+--------+
| expression_id | method                     | target | target_data_type | active |
|---------------+----------------------------+--------+------------------+--------|
|             4 | FULL_TEXT UNICODE_ANALYZER | LINE   | VARCHAR(2000)    | true   |
+---------------+----------------------------+--------+------------------+--------+

Use the wildcard (*) to enable search optimization on all qualifying columns

The following ALTER TABLE command enables FULL_TEXT search optimization on all four VARCHAR columns in the lines table:

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(*);
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DESCRIBE SEARCH OPTIMIZATION ON lines;
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+---------------+----------------------------+----------------+------------------+--------+
| expression_id | method                     | target         | target_data_type | active |
|---------------+----------------------------+----------------+------------------+--------|
|             1 | FULL_TEXT DEFAULT_ANALYZER | PLAY           | VARCHAR(50)      | true   |
|             2 | FULL_TEXT DEFAULT_ANALYZER | ACT_SCENE_LINE | VARCHAR(10)      | true   |
|             3 | FULL_TEXT DEFAULT_ANALYZER | CHARACTER      | VARCHAR(30)      | true   |
|             4 | FULL_TEXT DEFAULT_ANALYZER | LINE           | VARCHAR(2000)    | true   |
+---------------+----------------------------+----------------+------------------+--------+

Expected error when enabling FULL_TEXT optimization

The following ALTER TABLE command fails with an expected error because one of the specified columns is a NUMBER column:

ALTER TABLE lines ADD SEARCH OPTIMIZATION
  ON FULL_TEXT(play, speech_num, act_scene_line, character, line);
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001128 (42601): SQL compilation error: error line 1 at position 76
Expression FULL_TEXT(IDX_SRC_TABLE.SPEECH_NUM) cannot be used in search optimization.
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