Online DDL 是否锁表、是否rebuild表、inplace或copy算法的说明：

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原文： https://dev.MySQL.com/doc/refman/5.6/en/innodb-create-index-overview.html?spm=5176.100239.blogcont64664.13.SpL8lH

Operation	In-Place?	Rebuilds Table?	Permits Concurrent DML?	Only Modifies Metadata?	Notes
CREATE INDEX, ADD INDEX	Yes*	No*	Yes	No	Restrictions apply for FULLTEXT indexes; see next row.
ADD FULLTEXT INDEX	Yes*	No*	No	No	Adding the first FULLTEXT index rebuilds the table if there is no user-defined FTS_DOC_ID column. Subsequent FULLTEXT indexes may be added on the same table without rebuilding the table.
DROP INDEX	Yes	No	Yes	Yes	Only modifies table metadata.
OPTIMIZE TABLE	Yes*	Yes	Yes	No	Performed in-place as of MySQL 5.6.17. In-place operation is not supported for tables withFULLTEXT indexes.
Set column default value	Yes	No	Yes	Yes	Only modifies table metadata.
Change auto-incrementvalue	Yes	No	Yes	No*	Modifies a value stored in memory, not the data file.
Add foreign key constraint	Yes*	No	Yes	Yes	The INPLACE algorithm is supported when foreign_key_checks is disabled. Otherwise, only theCOPY algorithm is supported.
Drop foreign key constraint	Yes	No	Yes	Yes	foreign_key_checks can be enabled or disabled.
Rename column	Yes	No	Yes*	Yes	To permit concurrent DML, keep the same data type and only change the column name.
Add column	Yes	Yes	Yes*	No	Concurrent DML is not permitted when adding an auto-increment column. Data is reorganized substantially, making it an expensive operation.
Drop column	Yes	Yes	Yes	No	Data is reorganized substantially, making it an expensive operation.
Reorder columns	Yes	Yes	Yes	No	Data is reorganized substantially, making it an expensive operation.
Change ROW_FORMATproperty	Yes	Yes	Yes	No	Data is reorganized substantially, making it an expensive operation.
Change KEY_BLOCK_SIZEproperty	Yes	Yes	Yes	No	Data is reorganized substantially, making it an expensive operation.
Make column NULL	Yes	Yes*	Yes	No	Rebuilds the table in place. Data is reorganized substantially, making it an expensive operation.
Make column NOT NULL	Yes*	Yes*	Yes	No	Rebuilds the table in place. STRICT_ALL_TABLES or STRICT_TRANS_TABLES SQL_MODE is required for the operation to succeed. The operation fails if the column contains NULL values. As of 5.6.7, the server prohibits changes to foreign key columns that have the potential to cause loss of referential integrity. See Section 13.1.7, “ALTER TABLE Syntax”. Data is reorganized substantially, making it an expensive operation.
Change column data type	No	Yes	No	No	Only supports ALGORITHM=COPY
Add primary key	Yes*	Yes*	Yes	No	Rebuilds the table in place. Data is reorganized substantially, making it an expensive operation.ALGORITHM=INPLACE is not permitted under certain conditions if columns have to be converted toNOT NULL.
Drop primary key and add another	Yes	Yes	Yes	No	Data is reorganized substantially, making it an expensive operation.
Drop primary key	No	Yes	No	No	Only ALGORITHM=COPY supports dropping a primary key without adding a new one in the sameALTER TABLE statement.
Convert character set	No	Yes*	No	No	Rebuilds the table if the new character encoding is different.
Specify character set	No	Yes*	No	No	Rebuilds the table if the new character encoding is different.
Rebuild with FORCEoption	Yes*	Yes	Yes	No	Uses ALGORITHM=INPLACE as of MySQL 5.6.17. ALGORITHM=INPLACE is not supported for tables withFULLTEXT indexes.
“null” rebuild usingALTER TABLE ... ENGINE=INNODB	Yes*	Yes	Yes	No	Uses ALGORITHM=INPLACE as of MySQL 5.6.17. ALGORITHM=INPLACE is not supported for tables withFULLTEXT indexes.
Set STATS_PERSISTENT,STATS_AUTO_RECALC,STATS_SAMPLE_PAGESpersistent statisticsoptions	Yes	No	Yes	Yes	Only modifie

其余可参考文章： https://yq.aliyun.com/articles/64664

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