// Copyright 2018 PingCAP, Inc. // // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // // http://www.apache.org/licenses/LICENSE-2.0 // // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // See the License for the specific language governing permissions and // limitations under the License. package ddl import ( "fmt" "github.com/pingcap/parser/ast" ) // AlterAlgorithm is used to store supported alter algorithm. // For now, TiDB only support AlterAlgorithmInplace and AlterAlgorithmInstant. // The most alter operations are using instant algorithm, and only the add index is using inplace(not really inplace, // because we never block the DML but costs some time to backfill the index data) // See https://dev.mysql.com/doc/refman/8.0/en/alter-table.html#alter-table-performance. type AlterAlgorithm struct { // supported MUST store algorithms in the order 'INSTANT, INPLACE, COPY' supported []ast.AlgorithmType // If the alter algorithm is not given, the defAlgorithm will be used. defAlgorithm ast.AlgorithmType } var ( instantAlgorithm = &AlterAlgorithm{ supported: []ast.AlgorithmType{ast.AlgorithmTypeInstant}, defAlgorithm: ast.AlgorithmTypeInstant, } inplaceAlgorithm = &AlterAlgorithm{ supported: []ast.AlgorithmType{ast.AlgorithmTypeInplace}, defAlgorithm: ast.AlgorithmTypeInplace, } ) func getProperAlgorithm(specify ast.AlgorithmType, algorithm *AlterAlgorithm) (ast.AlgorithmType, error) { if specify == ast.AlgorithmTypeDefault { return algorithm.defAlgorithm, nil } r := ast.AlgorithmTypeDefault for _, a := range algorithm.supported { if specify <= a { r = a break } } var err error if specify != r { err = ErrAlterOperationNotSupported.GenWithStackByArgs(fmt.Sprintf("ALGORITHM=%s", specify), fmt.Sprintf("Cannot alter table by %s", specify), fmt.Sprintf("ALGORITHM=%s", algorithm.defAlgorithm)) } return r, err } // ResolveAlterAlgorithm resolves the algorithm of the alterSpec. // If specify is the ast.AlterAlgorithmDefault, then the default algorithm of the alter action will be returned. // If specify algorithm is not supported by the alter action, it will try to find a better algorithm in the order `INSTANT > INPLACE > COPY`, errAlterOperationNotSupported will be returned. // E.g. INSTANT may be returned if specify=INPLACE // If failed to choose any valid algorithm, AlgorithmTypeDefault and errAlterOperationNotSupported will be returned func ResolveAlterAlgorithm(alterSpec *ast.AlterTableSpec, specify ast.AlgorithmType) (ast.AlgorithmType, error) { switch alterSpec.Tp { // For now, TiDB only support inplace algorithm and instant algorithm. case ast.AlterTableAddConstraint: return getProperAlgorithm(specify, inplaceAlgorithm) default: return getProperAlgorithm(specify, instantAlgorithm) } }