However, some features of MySQL are not supported.
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This could be because there is now a better way to solve the problem (such as XML functions superseded by JSON), or a lack of current demand versus effort required (such as stored procedures and functions). Some features might also be difficult to implement as a distributed system. This page refers to general differences between MySQL and TiDB. GET_LOCK and RELEASE_LOCK functions #14994įeatures that are different from MySQL Auto-increment ID.CREATE TABLE tblName AS SELECT stmt syntax #4754.XA syntax (TiDB uses a two-phase commit internally, but this is not exposed via an SQL interface).Character sets other than utf8, utf8mb4, ascii, latin1 and binary.FULLTEXT/ SPATIAL functions and indexes #1793.Refer to the dedicated pages for Security and Pessimistic Transaction Model compatibility. In TiDB, auto-increment columns are only guaranteed to be unique and incremental on a single TiDB server, but they are not guaranteed to be incremental among multiple TiDB servers or allocated sequentially. Currently, TiDB allocates IDs in batches. If you insert data on multiple TiDB servers at the same time, the allocated IDs are not continuous. You can use the tidb_allow_remove_auto_inc system variable to enable or disable deleting the AUTO_INCREMENT attribute of a column. The syntax for deleting this column attribute is alter table modify or alter table change. Otherwise, an error might occur in the following situation.Īssume that you have a table with the auto-increment ID: CopyĬREATE TABLE t (id int unique key AUTO_INCREMENT, c int ) If you use auto-increment IDs in a cluster with multiple tidb-server instances, do not mix default values and custom values.
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The principle of the auto-increment ID in TiDB is that each tidb-server instance caches a section of ID values (currently 30000 IDs are cached) for allocation and fetches the next section after this section is used up.Īssume that the cluster contains two tidb-server instances, namely Instance A and Instance B.
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