I have two simple queries, one to read the table and one to update the table. How to lock the read of a select query while the update query is running. Now in MySQL InnoDB, I noticed that writes/updates are locked by default, but reads/selects get old data before the transaction.
I tried using a transaction in the update query and thenSELECT ... FOR UPDATE- outside the transaction - but it didn't seem to be successful. Also, for testing purposes, I'd like to know how to slow down UPDATE queries. I came across SLEEP(X) but I don't know how to implement it in an update query.
How to make each query wait for read/write until the write is completed.
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Using
READ-COMMITTEDtransactions will view the latest committed transaction. changes, and usingSELECT ... LOCK IN SHARE MODEwill cause reads to block until any outstanding updates are committed.Try this. In one screen, start transactions and updates. No SLEEP() is required, the transaction is just not committed. The lock created by UPDATE will continue to exist until you commit.
Don’t submit yet.
Meanwhile, in the second screen, set transaction isolation to read-commit transactions. There is no need to start an explicit transaction because InnoDB queries use transactions even if it is autocommitted.
The lock in shared mode makes it wait because there is still an outstanding exclusive lock created by the update.
In the first screen:
In the second screen, voila! The blocking read will unblock and you can see the results of the UDPATE immediately without flushing the transaction.