The following items apply to Disk Data storage requirements:
Variable-length columns of Disk Data tables take up a fixed amount of space. For each row, this is equal to the space required to store the largest possible value for that column.
For general information about calculating these values, see Section 10.5, “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 20.21, “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, convering a CHAR(4)
column
from memory-based to disk-based format increases the
amount of DataMemory
used per row from
4 to 8 bytes.
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.
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