mysql - Is it a good practice to have a lot of events? - mysql

Question

I have a table tblMatch :
+---------+---------------------+------------------+-----------+
| ID | start_date | end_date | status |
+---------+---------------------+------------------+-----------+
| 1 | 2017-12-09 03:23 | 2017-12-10 03:23 | 1 |
+---------+---------------------+------------------+-----------+
| ... | ... | ... | 1 |
+---------+---------------------+------------------+-----------+
| 1000000 | 2017-12-22 15:12 | 2017-12-30 15:12 | 1 |
+---------+---------------------+------------------+-----------+
When I insert a row, I create one event too.
Event will change status to 0 if the match is ended.
CREATE EVENT test_event_increment_number
ON SCHEDULE AT end_date
ON COMPLETION NOT PRESERVE
DO
UPDATE tblMatch SET status = 0 WHERE ID = increment_number;
If tblMatch has 100 million matches :
Does it effect server performance?
Is it bad or good idea to create a lot of events?

Answer 1

Create just 1 event that runs daily and closes the matches expiring that day.
CREATE EVENT test_event
ON SCHEDULE AT 1 every day
STARTS (TIMESTAMP(CURRENT_DATE) + INTERVAL 1 DAY)
DO
UPDATE tblMatch SET status = 0 WHERE end_date = CURRENT_DATE;
UPDATE
If you want to time your events at a minute level, then either change the frequency of your event to minute level and use minute level when determining if a match needs closing, or completely drop the status field and just use the end_date field's value compared to now() to determine if the event is closed. The latter is a better way.

Answer 2

I Create 25 events is different time. After a while, the database takes all the resources, and reboots.
CREATE EVENT `auction_event_46709`
ON SCHEDULE EVERY 5 MINUTE STARTS '2017-12-07 10:23:03'
ON COMPLETION NOT PRESERVE ENABLE
DO CALL auction_update_price(46709)
Procedure:
CREATE PROCEDURE `auction_update_price`( IN p_id INT )
BEGIN
DECLARE cur_price INT;
DECLARE stp_price INT;
DECLARE st_price INT;
DECLARE str_price INT;
SELECT current_price, step_price, stop_price, start_price INTO cur_price, stp_price, st_price, str_price FROM product_to_auction WHERE product_id = p_id;
IF( cur_price - stp_price > st_price ) THEN
UPDATE product_to_auction SET current_price = current_price - step_price WHERE current_price > stop_price AND product_id = p_id;
ELSE
UPDATE product_to_auction SET current_price = str_price WHERE product_id = p_id;
END IF;
END
How to Fix?

Answer 3

Don't use events at all for this sort of operation. Certainly don't use many events for it. Instead, use a query (or view) that takes your end_date into account and determines your status value dynamically based on date. For example, to retrieve a particular item by id, do this.
SELECT id, start_date, end_date
CASE WHEN end_date <= CURDATE() THEN 0 ELSE status END AS status
FROM tblMatch
WHERE id = something
This query returns the row from the table, along with the status value based on the moment you run the query. (I set it up so items with status = 0 are always marked as expired never mind the current time.)
If you want all the items with status 1 (meaning non expired) do this:
SELECT id, start_date, end_date, 1 AS status
FROM tblMatch
WHERE end_date < CURDATE ()
AND status = 1
If you MUST use an event, you can run it once a day, sometime after midnight to reset the status columns of all expiring rows to 0, with a query like this.
UPDATE tblMatch SET status = 0 WHERE status = 1 AND end_date < CURDATE();
(I prefer to run daily update queries shortly after 03:00 local time. Why? I'm located in the USA, and our daylight saving time switchover is done, twice a year, at 02:00 local time. Doing daily updates after 03:00 ensures they'll still work properly on switchover days. )
For these queries to be efficient, you need a compound index on (status, end_date)