Alter table INT value from signed to unsigned execution - mysql

Question

I have a table with the primary key of max signed INT hit, 2147483647
Imagine I want to switch it to unsigned, and there are no negative values in the table since it is a primary key, because Im under the current belief that it is the fastest way to get the table going again.
Should the ALTER TABLE statement to switch it to an unsigned INT be a relatively quick process, since the values of the ids shouldn't change? What about locking?

Answer 1

Mysql documentation on ALTER TABLE command describes quite in a detailed manner under "Storage, Performance, and Concurrency Considerations" section which changes can be done quickly, without table copy and index rebuild, and what locks mysql will apply during the course of the command. Changing the column type is unfortunately not listed as something that can be done in place (of course, read the documentation corresponding to your mysql version, I just linked the newest one).
For some operations, an in-place ALTER TABLE is possible that does not
require a temporary table:
For ALTER TABLE tbl_name RENAME TO new_tbl_name without any other options, MySQL simply renames any files that correspond to the table
tbl_name without making a copy. (You can also use the RENAME TABLE
statement to rename tables. See Section 13.1.28, “RENAME TABLE
Syntax”.) Any privileges granted specifically for the renamed table
are not migrated to the new name. They must be changed manually.
Alterations that modify only table metadata and not table data are immediate because the server only needs to alter the table .frm file,
not touch table contents. The following changes are fast alterations
that can be made this way:
Renaming a column.
Changing the default value of a column.
Changing the definition of an ENUM or SET column by adding new enumeration or set members to the end of the list of valid member
values, as long as the storage size of the data type does not change.
For example, adding a member to a SET column that has 8 members
changes the required storage per value from 1 byte to 2 bytes; this
will require a table copy. Adding members in the middle of the list
causes renumbering of existing members, which requires a table copy.
ALTER TABLE with DISCARD ... PARTITION ... TABLESPACE or IMPORT ... PARTITION ... TABLESPACE do not create any temporary tables or
temporary partition files.
ALTER TABLE with ADD PARTITION, DROP PARTITION, COALESCE PARTITION, REBUILD PARTITION, or REORGANIZE PARTITION does not create
any temporary tables (except when used with NDB tables); however,
these operations can and do create temporary partition files.
ADD or DROP operations for RANGE or LIST partitions are immediate operations or nearly so. ADD or COALESCE operations for HASH or KEY
partitions copy data between all partitions, unless LINEAR HASH or
LINEAR KEY was used; this is effectively the same as creating a new
table, although the ADD or COALESCE operation is performed partition
by partition. REORGANIZE operations copy only changed partitions and
do not touch unchanged ones.
Renaming an index.
Adding or dropping an index, for InnoDB.
Locking:
While ALTER TABLE is executing, the original table is readable by
other sessions (with the exception noted shortly). Updates and writes
to the table that begin after the ALTER TABLE operation begins are
stalled until the new table is ready, then are automatically
redirected to the new table without any failed updates. The temporary
copy of the original table is created in the database directory of the
new table. This can differ from the database directory of the original
table for ALTER TABLE operations that rename the table to a different
database.
The exception referred to earlier is that ALTER TABLE blocks reads
(not just writes) at the point where it is ready to install a new
version of the table .frm file, discard the old file, and clear
outdated table structures from the table and table definition caches.
At this point, it must acquire an exclusive lock. To do so, it waits
for current readers to finish, and blocks new reads (and writes).