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15.12.1 Online DDL Operations
Online support details, syntax examples, and usage notes for DDL operations are provided under the following topics in this section.
Index Operations
The following table provides an overview of online DDL support for index operations. An asterisk indicates additional information, an exception, or a dependency. For details, see Syntax and Usage Notes.
Table 15.17 Online DDL Support for Index Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Creating or adding a secondary index | No | Yes | No | Yes | No |
Dropping an index | No | Yes | No | Yes | Yes |
Renaming an index | No | Yes | No | Yes | Yes |
Adding a FULLTEXT index |
No | Yes* | No* | No | No |
Adding a SPATIAL index |
No | Yes | No | No | No |
Changing the index type | Yes | Yes | No | Yes | Yes |
Syntax and Usage Notes
Creating or adding a secondary index
The table remains available for read and write operations while the index is being created. The
CREATE INDEX
statement only finishes after all transactions that are accessing the table are completed, so that the initial state of the index reflects the most recent contents of the table.Online DDL support for adding secondary indexes means that you can generally speed the overall process of creating and loading a table and associated indexes by creating the table without secondary indexes, then adding secondary indexes after the data is loaded.
A newly created secondary index contains only the committed data in the table at the time the
CREATE INDEX
orALTER TABLE
statement finishes executing. It does not contain any uncommitted values, old versions of values, or values marked for deletion but not yet removed from the old index.Some factors affect the performance, space usage, and semantics of this operation. For details, see Section 15.12.6, “Online DDL Limitations”.
Dropping an index
The table remains available for read and write operations while the index is being dropped. The
DROP INDEX
statement only finishes after all transactions that are accessing the table are completed, so that the initial state of the index reflects the most recent contents of the table.Renaming an index
Adding a
FULLTEXT
indexAdding the first
FULLTEXT
index rebuilds the table if there is no user-definedFTS_DOC_ID
column. AdditionalFULLTEXT
indexes may be added without rebuilding the table.Adding a
SPATIAL
indexAdding the first
FULLTEXT
index rebuilds the table if there is no user-definedFTS_DOC_ID
column. AdditionalFULLTEXT
indexes may be added without rebuilding the table.Changing the index type (
USING {BTREE | HASH}
)
The following table provides an overview of online DDL support for primary key operations. An asterisk indicates additional information, an exception, or a dependency. See Syntax and Usage Notes.
Table 15.18 Online DDL Support for Primary Key Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Adding a primary key | No | Yes* | Yes* | Yes | No |
Dropping a primary key | No | No | Yes | No | No |
Dropping a primary key and adding another | No | Yes | Yes | Yes | No |
Syntax and Usage Notes
Adding a primary key
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
.Restructuring the clustered index always requires copying of table data. Thus, it is best to define the primary key when you create a table, rather than issuing
ALTER TABLE ... ADD PRIMARY KEY
later.When you create a
UNIQUE
orPRIMARY KEY
index, MySQL must do some extra work. ForUNIQUE
indexes, MySQL checks that the table contains no duplicate values for the key. For aPRIMARY KEY
index, MySQL also checks that none of thePRIMARY KEY
columns contains aNULL
.When you add a primary key using the
ALGORITHM=COPY
clause, MySQL convertsNULL
values in the associated columns to default values: 0 for numbers, an empty string for character-based columns and BLOBs, and 0000-00-00 00:00:00 forDATETIME
. This is a non-standard behavior that Oracle recommends you not rely on. Adding a primary key usingALGORITHM=INPLACE
is only permitted when theSQL_MODE
setting includes thestrict_trans_tables
orstrict_all_tables
flags; when theSQL_MODE
setting is strict,ALGORITHM=INPLACE
is permitted, but the statement can still fail if the requested primary key columns containNULL
values. TheALGORITHM=INPLACE
behavior is more standard-compliant.If you create a table without a primary key,
InnoDB
chooses one for you, which can be the firstUNIQUE
key defined onNOT NULL
columns, or a system-generated key. To avoid uncertainty and the potential space requirement for an extra hidden column, specify thePRIMARY KEY
clause as part of theCREATE TABLE
statement.MySQL creates a new clustered index by copying the existing data from the original table to a temporary table that has the desired index structure. Once the data is completely copied to the temporary table, the original table is renamed with a different temporary table name. The temporary table comprising the new clustered index is renamed with the name of the original table, and the original table is dropped from the database.
The online performance enhancements that apply to operations on secondary indexes do not apply to the primary key index. The rows of an InnoDB table are stored in a clustered index organized based on the primary key, forming what some database systems call an “index-organized table”. Because the table structure is closely tied to the primary key, redefining the primary key still requires copying the data.
When an operation on the primary key uses
ALGORITHM=INPLACE
, even though the data is still copied, it is more efficient than usingALGORITHM=COPY
because:No undo logging or associated redo logging is required for
ALGORITHM=INPLACE
. These operations add overhead to DDL statements that useALGORITHM=COPY
.The secondary index entries are pre-sorted, and so can be loaded in order.
The change buffer is not used, because there are no random-access inserts into the secondary indexes.
Dropping a primary key
Only
ALGORITHM=COPY
supports dropping a primary key without adding a new one in the sameALTER TABLE
statement.Dropping a primary key and adding another
Data is reorganized substantially, making it an expensive operation.
The following table provides an overview of online DDL support for column operations. An asterisk indicates additional information, an exception, or a dependency. For details, see Syntax and Usage Notes.
Table 15.19 Online DDL Support for Column Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Adding a column | Yes* | Yes | No* | Yes* | No |
Dropping a column | No | Yes | Yes | Yes | No |
Renaming a column | No | Yes | No | Yes* | Yes |
Reordering columns | No | Yes | Yes | Yes | No |
Setting a column default value | Yes | Yes | No | Yes | Yes |
Changing the column data type | No | No | Yes | No | No |
Extending VARCHAR column size |
No | Yes | No | Yes | Yes |
Dropping the column default value | Yes | Yes | No | Yes | Yes |
Changing the auto-increment value | No | Yes | No | Yes | No* |
Making a column NULL |
No | Yes | Yes* | Yes | No |
Making a column NOT NULL |
No | Yes* | Yes* | Yes | No |
Modifying the definition of an ENUM or
SET column |
Yes | Yes | No | Yes | Yes |
Syntax and Usage Notes
Adding a column
The following limitations apply when the
INSTANT
algorithm is used to add a column:Adding a column cannot be combined in the same statement with other
ALTER TABLE
actions that do not supportALGORITHM=INSTANT
.A column can only be added as the last column of the table. Adding a column to any other position among other columns is not supported.
Columns cannot be added to tables that use
ROW_FORMAT=COMPRESSED
.Columns cannot be added to tables that include a
FULLTEXT
index.Columns cannot be added to temporary tables. Temporary tables only support
ALGORITHM=COPY
.Columns cannot be added to tables that reside in the data dictionary tablespace.
Row size limits are not evaluated when adding a column. However, row size limits are checked during DML operations that insert and update rows in the table.
Multiple columns may be added in the same
ALTER TABLE
statement. For example:INFORMATION_SCHEMA.INNODB_TABLES
andINFORMATION_SCHEMA.INNODB_COLUMNS
provide metadata for instantly added columns.INFORMATION_SCHEMA.INNODB_TABLES.INSTANT_COLS
shows number of columns in the table prior to adding the first instant column.INFORMATION_SCHEMA.INNODB_COLUMNS.HAS_DEFAULT
andDEFAULT_VALUE
provide metadata about default values for instantly added columns.Concurrent DML is not permitted when adding an auto-increment column. Data is reorganized substantially, making it an expensive operation. At a minimum,
ALGORITHM=INPLACE, LOCK=SHARED
is required.The table is rebuilt if
ALGORITHM=INPLACE
is used to add a column.Dropping a column
Data is reorganized substantially, making it an expensive operation.
Renaming a column
To permit concurrent DML, keep the same data type and only change the column name.
When you keep the same data type and
[NOT] NULL
attribute, only changing the column name, the operation can always be performed online.You can also rename a column that is part of a foreign key constraint. The foreign key definition is automatically updated to use the new column name. Renaming a column participating in a foreign key only works with
ALGORITHM=INPLACE
. If you use theALGORITHM=COPY
clause, or some other condition causes the command to useALGORITHM=COPY
behind the scenes, theALTER TABLE
statement fails.ALGORITHM=INPLACE
is not supported for renaming a generated column.Reordering columns
To reorder columns, use
FIRST
orAFTER
inCHANGE
orMODIFY
operations.Data is reorganized substantially, making it an expensive operation.
Changing the column data type
Changing the column data type is only supported with
ALGORITHM=COPY
.Extending
VARCHAR
column sizeThe number of length bytes required by a
VARCHAR
column must remain the same. ForVARCHAR
columns of 0 to 255 bytes in size, one length byte is required to encode the value. ForVARCHAR
columns of 256 bytes in size or more, two length bytes are required. As a result, in-placeALTER TABLE
only supports increasingVARCHAR
column size from 0 to 255 bytes, or from 256 bytes to a greater size. In-placeALTER TABLE
does not support increasing the size of aVARCHAR
column from less than 256 bytes to a size equal to or greater than 256 bytes. In this case, the number of required length bytes changes from 1 to 2, which is only supported by a table copy (ALGORITHM=COPY
). For example, attempting to changeVARCHAR
column size for a single byte character set from VARCHAR(255) to VARCHAR(256) using in-placeALTER TABLE
returns this error:NoteThe byte length of a
VARCHAR
column is dependant on the byte length of the character set.Decreasing
VARCHAR
size using in-placeALTER TABLE
is not supported. DecreasingVARCHAR
size requires a table copy (ALGORITHM=COPY
).Setting a column default value
Only modifies table metadata. Default column values are stored in the data dictionary.
Dropping a column default value
Changing the auto-increment value
Modifies a value stored in memory, not the data file.
In a distributed system using replication or sharding, you sometimes reset the auto-increment counter for a table to a specific value. The next row inserted into the table uses the specified value for its auto-increment column. You might also use this technique in a data warehousing environment where you periodically empty all the tables and reload them, and restart the auto-increment sequence from 1.
Making a column
NULL
Rebuilds the table in place. Data is reorganized substantially, making it an expensive operation.
Making a column
NOT NULL
Rebuilds the table in place.
STRICT_ALL_TABLES
orSTRICT_TRANS_TABLES
SQL_MODE
is required for the operation to succeed. The operation fails if the column contains NULL values. The server prohibits changes to foreign key columns that have the potential to cause loss of referential integrity. See Section 13.1.9, “ALTER TABLE Syntax”. Data is reorganized substantially, making it an expensive operation.Modifying the definition of an
ENUM
orSET
columnModifying the definition of an
ENUM
orSET
column by adding new enumeration or set members to the end of the list of valid member values may be performed instantly or in place, as long as the storage size of the data type does not change. For example, adding a member to aSET
column that has 8 members changes the required storage per value from 1 byte to 2 bytes; this requires a table copy. Adding members in the middle of the list causes renumbering of existing members, which requires a table copy.
The following table provides an overview of online DDL support for generated column operations. For details, see Syntax and Usage Notes.
Table 15.20 Online DDL Support for Generated Column Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Adding a STORED column |
No | No | Yes | No | No |
Modifying STORED column order |
No | No | Yes | No | No |
Dropping a STORED column |
No | Yes | Yes | Yes | No |
Adding a VIRTUAL column |
Yes | Yes | No | Yes | Yes |
Modifying VIRTUAL column order |
No | No | Yes | No | No |
Dropping a VIRTUAL column |
Yes | Yes | No | Yes | Yes |
Syntax and Usage Notes
Adding a
STORED
columnADD COLUMN
is not an in-place operation for stored columns (done without using a temporary table) because the expression must be evaluated by the server.Modifying
STORED
column orderRebuilds the table in place.
Dropping a
STORED
columnRebuilds the table in place.
Adding a
VIRTUAL
columnAdding a virtual column can be performed instantly or in place for non-partitioned tables.
Adding a
VIRTUAL
is not an in-place operation for partitioned tables.Modifying
VIRTUAL
column orderDropping a
VIRTUAL
columnDropping a
VIRTUAL
column can be performed instantly or in place for non-partitioned tables.
The following table provides an overview of online DDL support for foreign key operations. An asterisk indicates additional information, an exception, or a dependency. For details, see Syntax and Usage Notes.
Table 15.21 Online DDL Support for Foreign Key Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Adding a foreign key constraint | No | Yes* | No | Yes | Yes |
Dropping a foreign key constraint | No | Yes | No | Yes | Yes |
Syntax and Usage Notes
Adding a foreign key constraint
The
INPLACE
algorithm is supported whenforeign_key_checks
is disabled. Otherwise, only theCOPY
algorithm is supported.Dropping a foreign key constraint
Dropping a foreign key can be performed online with the
foreign_key_checks
option enabled or disabled.If you do not know the names of the foreign key constraints on a particular table, issue the following statement and find the constraint name in the
CONSTRAINT
clause for each foreign key:Or, query the
INFORMATION_SCHEMA.TABLE_CONSTRAINTS
table and use theCONSTRAINT_NAME
andCONSTRAINT_TYPE
columns to identify the foreign key names.You can also drop a foreign key and its associated index in a single statement:
If foreign keys are
already present in the table being altered (that is, it is a
child table containing
a FOREIGN KEY ... REFERENCE
clause),
additional restrictions apply to online DDL operations, even
those not directly involving the foreign key columns:
An
ALTER TABLE
on the child table could wait for another transaction to commit, if a change to the parent table causes associated changes in the child table through anON UPDATE
orON DELETE
clause using theCASCADE
orSET NULL
parameters.In the same way, if a table is the parent table in a foreign key relationship, even though it does not contain any
FOREIGN KEY
clauses, it could wait for theALTER TABLE
to complete if anINSERT
,UPDATE
, orDELETE
statement causes anON UPDATE
orON DELETE
action in the child table.
The following table provides an overview of online DDL support for table operations. An asterisk indicates additional information, an exception, or a dependency. For details, see Syntax and Usage Notes.
Table 15.22 Online DDL Support for Table Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Changing the ROW_FORMAT |
No | Yes | Yes | Yes | No |
Changing the KEY_BLOCK_SIZE |
No | Yes | Yes | Yes | No |
Setting persistent table statistics | No | Yes | No | Yes | Yes |
Specifying a character set | No | Yes | Yes* | No | No |
Converting a character set | No | No | Yes* | No | No |
Optimizing a table | No | Yes* | Yes | Yes | No |
Rebuilding with the FORCE option |
No | Yes* | Yes | Yes | No |
Performing a null rebuild | No | Yes* | Yes | Yes | No |
Renaming a table | Yes | Yes | No | Yes | Yes |
Syntax and Usage Notes
Changing the
ROW_FORMAT
Data is reorganized substantially, making it an expensive operation.
For additional information about the
ROW_FORMAT
option, see Table Options.Changing the
KEY_BLOCK_SIZE
Data is reorganized substantially, making it an expensive operation.
For additional information about the
KEY_BLOCK_SIZE
option, see Table Options.Setting persistent table statistics options
Only modifies table metadata.
Persistent statistics include
STATS_PERSISTENT
,STATS_AUTO_RECALC
, andSTATS_SAMPLE_PAGES
. For more information, see Section 15.8.10.1, “Configuring Persistent Optimizer Statistics Parameters”.Specifying a character set
Rebuilds the table if the new character encoding is different.
Converting a character set
Rebuilds the table if the new character encoding is different.
Optimizing a table
In-place operation is not supported for tables with
FULLTEXT
indexes. The operation uses theINPLACE
algorithm, butALGORITHM
andLOCK
syntax is not permitted.Rebuilding a table with the
FORCE
optionUses
ALGORITHM=INPLACE
as of MySQL 5.6.17.
ALGORITHM=INPLACE
is not supported for tables withFULLTEXT
indexes.Performing a "null" rebuild
Uses
ALGORITHM=INPLACE
as of MySQL 5.6.17.ALGORITHM=INPLACE
is not supported for tables withFULLTEXT
indexes.Renaming a table
Renaming a table can be performed instantly or in place. MySQL renames files that correspond to the table
tbl_name
without making a copy. (You can also use theRENAME TABLE
statement to rename tables. See Section 13.1.36, “RENAME TABLE Syntax”.) Privileges granted specifically for the renamed table are not migrated to the new name. They must be changed manually.
The following table provides an overview of online DDL support for tablespace operations. For details, see Syntax and Usage Notes.
Table 15.23 Online DDL Support for Tablespace Operations
Operation | Instant | In Place | Rebuilds Table | Permits Concurrent DML | Only Modifies Metadata |
---|---|---|---|---|---|
Renaming a general tablespace | No | Yes | No | Yes | Yes |
Enabling or disabling general tablespace encryption | No | Yes | No | Yes | No |
Enabling or disabling file-per-table tablespace encryption | No | No | Yes | No | No |
Syntax and Usage Notes
Renaming a general tablespace
ALTER TABLESPACE ... RENAME TO
uses theINPLACE
algorithm but does not support theALGORITHM
clause.Enabling or disabling general tablespace encryption
ALTER TABLESPACE ... ENCRYPTION
uses theINPLACE
algorithm but does not support theALGORITHM
clause.For related information, see Section 15.6.3.9, “InnoDB Data-at-Rest Encryption”.
Enabling or disabling file-per-table tablespace encryption
For related information, see Section 15.6.3.9, “InnoDB Data-at-Rest Encryption”.
With the exception of some ALTER
TABLE
partitioning clauses, online DDL operations for
partitioned InnoDB
tables follow the same
rules that apply to regular InnoDB
tables.
Some ALTER TABLE
partitioning
clauses do not go through the same internal online DDL API as
regular non-partitioned InnoDB
tables. As a
result, online support for ALTER
TABLE
partitioning clauses varies.
The following table shows the online status for each
ALTER TABLE
partitioning statement.
Regardless of the online DDL API that is used, MySQL attempts to
minimize data copying and locking where possible.
ALTER TABLE
partitioning options
that use ALGORITHM=COPY
or that only permit
“ALGORITHM=DEFAULT,
LOCK=DEFAULT
”, repartition the table using the
COPY
algorithm. In other words, a new
partitioned table is created with the new partitioning scheme.
The newly created table includes any changes applied by the
ALTER TABLE
statement, and table
data is copied into the new table structure.
Table 15.24 Online DDL Support for Partitioning Operations
Partitioning Clause | Instant | In Place | Permits DML | Notes |
---|---|---|---|---|
PARTITION BY |
No | No | No | Permits ALGORITHM=COPY ,
LOCK={DEFAULT|SHARED|EXCLUSIVE} |
ADD PARTITION |
No | Yes* | Yes* | ALGORITHM=INPLACE,
LOCK={DEFAULT|NONE|SHARED|EXCLUSISVE} is
supported for RANGE and
LIST partitions,
ALGORITHM=INPLACE,
LOCK={DEFAULT|SHARED|EXCLUSISVE} for
HASH and KEY
partitions, and ALGORITHM=COPY,
LOCK={SHARED|EXCLUSIVE} for all partition types.
Does not copy existing data for tables partitioned by
RANGE or LIST .
Concurrent queries are permitted with
ALGORITHM=COPY for tables partitioned
by HASH or LIST , as
MySQL copies the data while holding a shared lock. |
DROP PARTITION |
No | Yes* | Yes* |
|
DISCARD PARTITION |
No | No | No | Only permits ALGORITHM=DEFAULT ,
LOCK=DEFAULT |
IMPORT PARTITION |
No | No | No | Only permits ALGORITHM=DEFAULT ,
LOCK=DEFAULT |
TRUNCATE
PARTITION |
No | Yes | Yes | Does not copy existing data. It merely deletes rows; it does not alter the definition of the table itself, or of any of its partitions. |
COALESCE
PARTITION |
No | Yes* | No | ALGORITHM=INPLACE, LOCK={DEFAULT|SHARED|EXCLUSIVE} is
supported. |
REORGANIZE
PARTITION |
No | Yes* | No | ALGORITHM=INPLACE, LOCK={DEFAULT|SHARED|EXCLUSIVE} is
supported. |
EXCHANGE
PARTITION |
No | Yes | Yes | |
ANALYZE PARTITION |
No | Yes | Yes | |
CHECK PARTITION |
No | Yes | Yes | |
OPTIMIZE
PARTITION |
No | No | No | ALGORITHM and LOCK clauses are
ignored. Rebuilds the entire table. See
Section 23.3.4, “Maintenance of Partitions”. |
REBUILD PARTITION |
No | Yes* | No | ALGORITHM=INPLACE, LOCK={DEFAULT|SHARED|EXCLUSIVE} is
supported. |
REPAIR PARTITION |
No | Yes | Yes | |
REMOVE
PARTITIONING |
No | No | No | Permits ALGORITHM=COPY ,
LOCK={DEFAULT|SHARED|EXCLUSIVE} |
Non-partitioning online ALTER
TABLE
operations on partitioned tables follow the same
rules that apply to regular tables. However,
ALTER TABLE
performs online
operations on each table partition, which causes increased
demand on system resources due to operations being performed on
multiple partitions.
For additional information about ALTER
TABLE
partitioning clauses, see
Partitioning Options, and
Section 13.1.9.1, “ALTER TABLE Partition Operations”. For
information about partitioning in general, see
Chapter 23, Partitioning.
Document created the 26/06/2006, last modified the 26/10/2018
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