Monday, November 6, 2017

SKIP LOCKED

SKIP LOCKED is a new feature in MySQL 8 that many will find valuable.  If allows you to not wait about for locked records and work on what is available -- the unlocked records.

How To Use SKIP LOCKED

The MySQL world database has 274 records in the city table where the countryCode field equals 'USA' there are 274 records. From past interactions, we somehow know there are some records with the ID field greater than 4000.

On MySQL shell number 1, start a transaction and lock some records
mysql>START TRANSACTION;
mysql>SELECT * FROM city WHERE ID > 4000 and countryCode = 'USA';
There will be 66 records.

On MySQL shell number number 2, start a transaction and lets try to lock the records starting at IS 3990 and up.
mysql>START TRANSACTION;
mysql>SELECT FROM city WHERE id > 3990 and countryCode='USA'
FOR UPDATE SKIPPED LOCKED;
There will be 10 records.  The records 4000 and up are locked by the transaction on the other shell.  

So no more hanging around for locked records.  You can process what is available at the current time.  So in situations where you are vending seats, hotel rooms, rental cares, or what have you -- you can find out what records are not locked by others and process them.

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