Online Operations with ALTER TABLE in NDB Cluster For general information about calculating these values, see Section 11.7, “Data Type Storage Requirements” . You can obtain an estimate the amount of space available in data files and undo log files by querying the INFORMATION_SCHEMA.FILES  table. For more information and examples, see Section 26.3.15, “The INFORMATION_SCHEMA FILES Table” . The  OPTIMIZE TABLE  statement does not have any effect on Disk Data tables. •In a Disk Data table, the first 256 bytes of a  TEXT  or  BLOB  column are stored in memory; only the remainder is stored on disk. •Each row in a Disk Data table uses 8 bytes in memory to point to the data stored on disk. This means that, in some cases, converting an in-memory column to the disk-based format can actually result in greater memory usage. For example, converting a  CHAR(4)  column from memory-based to disk-based format increases the amount of  DataMemory  used per row from 4 to 8 bytes. Note Important Starting the cluster with the  --initial  option does  not  remove Disk Data files. You must remove these manually prior to performing an initial restart of the cluster. Performance of Disk Data tables can be improved by minimizing the number of disk seeks by making sure that  DiskPageBufferMemory  is of sufficient size. You can query the  diskpagebuffer  table to help determine whether the value for this parameter needs to be increased. MySQL NDB Cluster 8.0 supports online table schema changes using the standard  ALTER TABLE  syntax employed by the MySQL Server ( ALGORITHM=DEFAULT|INPLACE|COPY ), and described elsewhere. Some older releases of NDB Cluster used a syntax specific to  NDB  for online  ALTER TABLE  operations. That syntax has since been removed. Operations that add and drop indexes on variable-width columns of  NDB  tables occur online. Online operations are noncopying; that is, they do not require that indexes be re-created. They do not lock the table being altered from access by other API nodes in an NDB Cluster (but see Limitations of NDB online operations, later in this section). Such operations do not require single user mode for  NDB  table alterations made in an NDB cluster with multiple API nodes; transactions can continue uninterrupted during online DDL operations. ALGORITHM=INPLACE  can be used to perform online  ADD COLUMN ,  ADD INDEX  (including  CREATE INDEX  statements), and  DROP INDEX  operations on  NDB  tables. Online renaming of  NDB  tables is also supported. Previously, columns of  NDB  tables could not be renamed online; this limitation is removed in NDB 8.0.18. Currently you cannot add disk-based columns to  NDB  tables online. This means that, if you wish to add an in-memory column to an  NDB  table that uses a table-level  STORAGE DISK  option, you must declare the new column as using memory-based storage explicitly. For example—assuming that you have already created tablespace  ts1 —suppose that you create table  t1  as follows: mysql>  CREATE TABLE t1 ( 23.5.11 Online Operations with ALTER TABLE in NDB Cluster Note 4504