官术网_书友最值得收藏!

Defining GIN indexes

If you want to apply text search to a column or a group of columns, there are basically two choices:

  • Create a functional index using GIN
  • Add a column containing ready to use tsvectors and a trigger to keep them in sync

In this section, both options will be outlines. To show how things work, I have created some sample data:

test=# CREATE TABLE t_fts AS SELECT comment FROM pg_available_extensions;
SELECT 43

Indexing the column directly with a functional index is definitely a slower but more space-efficient way to get things done:

test=# CREATE INDEX idx_fts_func ON t_fts USING gin(to_tsvector('english', comment)); 
CREATE INDEX

Deploying an index on the function is easy but it can lead to some overhead. Adding a materialized column needs more space but will lead to better runtime behavior:

test=# ALTER TABLE t_fts ADD COLUMN ts tsvector; 
ALTER TABLE

The only trouble is: how do you keep this column in sync? The answer is by using a trigger:

test=# CREATE TRIGGER tsvectorupdate  
BEFORE INSERT OR UPDATE ON t_fts
FOR EACH ROW
EXECUTE PROCEDURE
tsvector_update_trigger(somename, 'pg_catalog.english', "comment");

Fortunately, PostgreSQL already provides a C function that can be used by a trigger to sync the tsvector column. Just pass a name, the desired language, as well as a couple of columns to the function, and you are already done. The trigger function will take care of all that is needed. Note that a trigger will always operate within the same transaction as the statement making the modification. Therefore there is no risk of being inconsistent.

主站蜘蛛池模板: 灌南县| 抚顺市| 蓬安县| 娱乐| 丹凤县| 鹿邑县| 石林| 简阳市| 长海县| 通州区| 汉阴县| 巴彦淖尔市| 浦东新区| 双江| 阜平县| 太仆寺旗| 涟源市| 乳山市| 福泉市| 临洮县| 北辰区| 资兴市| 金华市| 贺兰县| 肃北| 深州市| 类乌齐县| 秭归县| 嵩明县| 嘉峪关市| 寿阳县| 崇义县| 贵南县| 深圳市| 竹溪县| 桓台县| 竹北市| 镇原县| 孟津县| 黄大仙区| 淮安市|