Server System Variables
502
Range
1024 .. 4294967295
The maximum size of internal in-memory temporary tables. (The actual limit is determined as the
minimum of
tmp_table_size
[501]
and
max_heap_table_size
[468]
.) If an in-memory
temporary table exceeds the limit, MySQL automatically converts it to an on-disk
MyISAM
table.
Increase the value of
tmp_table_size
[501]
(and
max_heap_table_size
[468]
if necessary)
if you do many advanced
GROUP BY
queries and you have lots of memory. This variable does not
apply to user-created
MEMORY
tables.
You can compare the number of internal on-disk temporary tables created to the
total number of internal temporary tables created by comparing the values of the
Created_tmp_disk_tables
[524]
and
Created_tmp_tables
[524]
variables.
See also
Section 8.8.5, “How MySQL Uses Internal Temporary Tables”
.
•
tmpdir
[502]
Command-Line Format
--tmpdir=path
-t
Option-File Format
tmpdir
Option Sets Variable
Yes,
tmpdir
[502]
Variable Name
tmpdir
Variable Scope
Global
Dynamic Variable
No
Permitted Values
Type
file name
The directory used for temporary files and temporary tables. This variable can be set to a list of
several paths that are used in round-robin fashion. Paths should be separated by colon characters
(“
:
”) on Unix and semicolon characters (“
;
”) on Windows, NetWare, and OS/2.
The multiple-directory feature can be used to spread the load between several physical disks. If
the MySQL server is acting as a replication slave, you should not set
tmpdir
[502]
to point to
a directory on a memory-based file system or to a directory that is cleared when the server host
restarts. A replication slave needs some of its temporary files to survive a machine restart so that
it can replicate temporary tables or
LOAD DATA INFILE
operations. If files in the temporary file
directory are lost when the server restarts, replication fails. You can set the slave's temporary
directory using the
slave_load_tmpdir
[1465]
variable. In that case, the slave will not use the
general
tmpdir
[502]
value and you can set
tmpdir
[502]
to a nonpermanent location.
•
transaction_alloc_block_size
[502]
Command-Line Format
--transaction_alloc_block_size=#
Option-File Format
transaction_alloc_block_size
Option Sets Variable
Yes,
transaction_alloc_block_size
[502]
Variable Name
transaction_alloc_block_size
Variable Scope
Global, Session
Dynamic Variable
Yes
Permitted Values
Platform
Bit Size
32
Type
numeric
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