30 lines
1.3 KiB
Go
30 lines
1.3 KiB
Go
// Copyright 2024 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package ddl is the core of TiDB DDL layer. It is used to manage the schema of
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// TiDB Cluster.
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//
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// TiDB executes using the Online DDL algorithm, see docs/design/2018-10-08-online-DDL.md
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// for more details.
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//
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// DDL maintains the following invariant:
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//
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// At any time, for each schema object, such as a table, there are at most 2 versions
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// can exist for it, current version N loaded by all TiDBs and version N+1 pushed
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// forward by DDL, before we can finish the DDL or continue to next operation, we
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// need to make sure all TiDBs have synchronized to version N+1.
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// Note that we are using a global version number for all schema objects, so the
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// versions related some table might not be continuous, as DDLs are executed in parallel.
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package ddl
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