Rechercher dans le manuel MySQL
15.12.4 Simplifying DDL Statements with Online DDL
Before the introduction of online
DDL, it was common practice to combine many DDL operations
into a single ALTER TABLE
statement. Because each ALTER TABLE
statement involved copying and rebuilding the table, it was more
efficient to make several changes to the same table at once, since
those changes could all be done with a single rebuild operation
for the table. The downside was that SQL code involving DDL
operations was harder to maintain and to reuse in different
scripts. If the specific changes were different each time, you
might have to construct a new complex ALTER
TABLE
for each slightly different scenario.
For DDL operations that can be done online, you can separate them
into individual ALTER TABLE
statements for easier scripting and maintenance, without
sacrificing efficiency. For example, you might take a complicated
statement such as:
and break it down into simpler parts that can be tested and performed independently, such as:
You might still use multi-part ALTER
TABLE
statements for:
Operations that must be performed in a specific sequence, such as creating an index followed by a foreign key constraint that uses that index.
Operations all using the same specific
LOCK
clause, that you want to either succeed or fail as a group.Operations that cannot be performed online, that is, that still use the table-copy method.
Operations for which you specify
ALGORITHM=COPY
orold_alter_table=1
, to force the table-copying behavior if needed for precise backward-compatibility in specialized scenarios.
Document created the 26/06/2006, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/mysql-rf-innodb-online-ddl-single-multi.html
The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.
References
These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.