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NOWAIT
Last updated: 2024-04-25 11:00:51
Overview
DDL statements support
NO_WAIT and WAIT options. If a DDL statement with WAIT enabled fails to obtain an MDL lock, it will wait for WAIT seconds before it directly returns the query result. If a DDL statement with NO_WAIT enabled, it will directly return the query result without waiting for the MDL lock.SELECT FOR UPDATE statement supports
NOWAIT and SKIP LOCKED options. If target rows are locked by another transaction, a SELECT FOR UPDATE statement is supposed to wait for the transaction to release the lock. But in some use cases like flash sales, you do not want to wait for a lock. You can use SKIP LOCKED to skip locked rows (as a result, the locked rows won't be returned in the query result set) or NOWAIT to return an error without waiting for the lock.Note that
NO_WAIT and NOWAIT are different keywords.Supported Versions
TDSQL-C for MySQL 5.7 (kernel version 2.0.23/2.1.9) or later.
TDSQL-C for MySQL 8.0 (kernel version 3.1.10) or later.
Use Cases
Currently, DevAPI/XPlugin does not support using
SKIP LOCKED or NOWAIT in SELECT FOR UPDATE/SHARE statements. Note that NO_WAIT in DDL statements and NOWAIT in SELECT FOR UPDATE statements are different keywords for historical reasons.
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