Oracle 5.0 Reference Manual page 1326

CREATE TABLE lookup
(id INT, INDEX USING HASH (id))
ENGINE = MEMORY;
CREATE TABLE lookup
(id INT, INDEX USING BTREE (id))
ENGINE = MEMORY;
For general characteristics of B-tree and hash indexes, see
Indexes".
• If a table hash index has a high degree of key duplication (many index entries containing the
MEMORY
same value), updates to the table that affect key values and all deletes are significantly slower. The
degree of this slowdown is proportional to the degree of duplication (or, inversely proportional to the
index cardinality). You can use a
• tables can have nonunique keys. (This is an uncommon feature for implementations of hash
MEMORY
indexes.)
• Columns that are indexed can contain
• tables use a fixed-length row-storage format. Variable-length types such as
MEMORY
stored using a fixed length.
• tables cannot contain
MEMORY
• includes support for
MEMORY
• supports
MEMORY INSERT
• Non-TEMPORARY MEMORY
table.
• table contents are stored in memory, which is a property that
MEMORY
internal temporary tables that the server creates on the fly while processing queries. However, the
two types of tables differ in that
internal temporary tables are:
• tables are never converted to disk tables. If an internal temporary table becomes too
MEMORY
large, the server automatically converts it to on-disk storage, as described in
MySQL Uses Internal Temporary
• The maximum size of
variable, which has a default value of 16MB. To have larger (or smaller)
change the value of this variable. The value in effect for
life of the table. (If you use
becomes the new maximum size for the table. A server restart also sets the maximum size of
existing tables to the global
MEMORY
for individual tables as described later in this section.
• The server needs sufficient memory to maintain all
• Memory is not reclaimed if you delete individual rows from a
when the entire table is deleted. Memory that was previously used for rows that have been deleted
will be re-used for new rows only within the same table. To free up the memory used by rows that
have been deleted, use
To free all the memory used by a
execute or
DELETE TRUNCATE TABLE
DROP TABLE.
• If you want to populate a
[409] option. For example, you can put statements such as
file
The (HEAP) Storage Engine
MEMORY
index to avoid this problem.
BTREE
values.
NULL
or columns.
BLOB TEXT
AUTO_INCREMENT
DELAYED. See Section 13.2.5.2,
tables are shared among all clients, just like any other
tables are not subject to storage conversion, whereas
MEMORY
Tables".
tables is limited by the
MEMORY
or
ALTER TABLE
max_heap_table_size
ALTER TABLE ENGINE=MEMORY
table when you no longer require its contents, you should
MEMORY
to remove all rows, or remove the table altogether using
table when the MySQL server starts, you can use the
MEMORY
1306
Section 8.5.3, "How MySQL Uses
columns.
"INSERT DELAYED
MEMORY
max_heap_table_size
CREATE TABLE
TABLE, the value in effect at that time
TRUNCATE
[468]
tables that are in use at the same time.
MEMORY
table. Memory is reclaimed only
MEMORY
to force a table rebuild.
INSERT INTO ... SELECT
VARCHAR
Syntax".
non-TEMPORARY
tables share with
Section 8.8.5, "How
[468] system
tables, you must
MEMORY
is the value used for the
value.) You can set the size
--init-
are
or