Doublewrite Buffer When the  AUTOEXTEND_SIZE  setting for a tablespace is altered, the first extension that occurs afterward increases the tablespace size to a multiple of the  AUTOEXTEND_SIZE  setting. Subsequent extensions are of the configured size. When a file-per-table or general tablespace is created with a non-zero  AUTOEXTEND_SIZE  setting, the tablespace is initialized at the specified  AUTOEXTEND_SIZE  size. ALTER TABLESPACE  cannot be used to configure the  AUTOEXTEND_SIZE  of a file-per-table tablespace. ALTER TABLE  must be used. For tables created in file-per-table tablespaces,  SHOW CREATE TABLE  shows the  AUTOEXTEND_SIZE option only when it is configured to a non-zero value. To determine the  AUTOEXTEND_SIZE  for any  InnoDB  tablespace, query the INFORMATION_SCHEMA.INNODB_TABLESPACES  table. For example: mysql>  SELECT NAME, AUTOEXTEND_SIZE FROM INFORMATION_SCHEMA.INNODB_TABLESPACES  WHERE NAME LIKE ’test/t1’; +---------+-----------------+ | NAME | AUTOEXTEND_SIZE | +---------+-----------------+ | test/t1 | 4194304 | +---------+-----------------+ mysql>  SELECT NAME, AUTOEXTEND_SIZE FROM INFORMATION_SCHEMA.INNODB_TABLESPACES  WHERE NAME LIKE ’ts1’; +------+-----------------+ | NAME | AUTOEXTEND_SIZE | +------+-----------------+ | ts1 | 4194304 | +------+-----------------+ Note 15.6.4 Doublewrite Buffer An  AUTOEXTEND_SIZE  of 0, which is the default setting, means that the tablespace is extended according to the default tablespace extension behavior described above. The doublewrite buffer is a storage area where  InnoDB  writes pages flushed from the buffer pool before writing the pages to their proper positions in the  InnoDB  data files. If there is an operating system, storage subsystem, or unexpected  mysqld  process exit in the middle of a page write,  InnoDB  can find a good copy of the page from the doublewrite buffer during crash recovery. Although data is written twice, the doublewrite buffer does not require twice as much I/O overhead or twice as many I/O operations. Data is written to the doublewrite buffer in a large sequential chunk, with a single  fsync()  call to the operating system (except in the case that  innodb_flush_method  is set to O_DIRECT_NO_FSYNC ). Prior to MySQL 8.0.20, the doublewrite buffer storage area is located in the  InnoDB  system tablespace. As of MySQL 8.0.20, the doublewrite buffer storage area is located in doublewrite files. The following variables are provided for doublewrite buffer configuration: • innodb_doublewrite The  innodb_doublewrite  variable controls whether the doublwrite buffer is enabled. It is enabled by default in most cases. To disable the doublewrite buffer, set  innodb_doublewrite  to 0 or start the 3072