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What is waiting for table metadata lock?
What does metadata lock wait mean? When there is an active transaction (explicit or implicit) on the table, MySQL does not allow writing of data to metadata. It does this to maintain metadata consistency in the table in a concurrent environment.
What is waiting for table flush?
If a query is running that accesses that table at the time the the FLUSH TABLE is issued, the FLUSH TABLE will be blocked until the query completes. While the FLUSH TABLE is blocked, no new queries accessing the affected tables can start running and their state in the process list will show “Waiting for table flush“.
How do I flush a table in mysql?
To flush and lock tables, use FLUSH TABLES tbl_name WITH READ LOCK instead. With a list of one or more comma-separated table names, this operation is like FLUSH TABLES with no names except that the server flushes only the named tables. If a named table does not exist, no error occurs.
Why is MySQL waiting for table level lock?
At first glance, you want to do that on ID and username columns in the user table. Check the storage engine of the table .Change to Innodb if possible as it cause only row level locking. The queries which are running may be forcing a table lock even if you are using innodb tables if you are not using the index .
Why does Stack Overflow keep forcing a table lock?
Check the storage engine of the table .Change to Innodb if possible as it cause only row level locking. The queries which are running may be forcing a table lock even if you are using innodb tables if you are not using the index . Thanks for contributing an answer to Stack Overflow!
How to prevent Lock escalation on a table?
Therefore, one method to prevent lock escalation on a particular table is to acquire and hold a lock on a different connection that is not compatible with the escalated lock type. An IX (intent exclusive) lock at the table level does not lock any rows or pages, but it is still not compatible with an escalated S (shared) or X (exclusive) TAB lock.
What causes a query to exceed the Lock escalation threshold?
This means that what may look like a SELECT statement at a “read-committed” isolation level might acquire many thousands of key locks (on both the clustered index and one nonclustered index). This can cause such a query to exceed the lock escalation thresholds.