There are some options that can cause temp tables to materialize as MyISAM tables or can be configured to delay it. Keep in mind that for disk-based temp tables, there are no .frm files, but only .MYD and .MYI files (of course. the .MYI file is never used since it is impossible index an internal temp table).

Here are the options:

• Temp Table Variables That Should Be the Same Size
  • tmp_table_size
  • max_heap_table_size
• sort_buffer_size
• join_buffer_size

You should also consider the MySQL Documentation on Internal Temp Table Usage

The situations where in-memory temp tables are made are

• If there is an ORDER BY clause and a different GROUP BY clause, or if the ORDER BY or GROUP BY contains columns from tables other than the first table in the join queue, a temporary table is created.
• DISTINCT combined with ORDER BY may require a temporary table.
• If you use the SQL_SMALL_RESULT option, MySQL uses an in-memory temporary table, unless the query also contains elements (described later) that require on-disk storage.

When an in-memory temp table exceeded the minimum of (tmp_table_size or max_heap_table_size), mysqld does the following:

• Suspends the query
• Copies the in-memory table's contents into a MyISAM temp table
• Discards the in-memory table
• Continues the query, sending the temp data into the MyISAM temp table

The situations where in-memory temp tables are bypassed in favor of disk are

• Presence of a BLOB or TEXT column in the table
• Presence of any column in a GROUP BY or DISTINCT clause larger than 512 bytes
• Presence of any column larger than 512 bytes in the SELECT list, if UNION or UNION ALL is used

Some due diligence is required to reduce temp table creation on disk

• Setting join_buffer_size bigger
• Setting sort_buffer_size bigger
• Setting tmp_table_size and max_heap_table_size bigger
• Tuning queries to minimize or even prevent temp tables
• Creating indexes to create presorted view of data from individual tables
• Installing additional RAM to accommodate large in-memory temp tables

If after such due diligence, there are still temp tables being formed on Disk, here is one desperate move: Mapping disk-based temp table creation to memory.

Here is a quick-and-dirty way to set up a 16GB RAM Disk using tmpdir

STEP01) Create RAM Disk Folder

mkdir /var/mysql_tmpfs

STEP02) Add this to my.cnf

[mysqld]
tmpdir=/var/mysql_tmpfs

STEP03) Add this to /etc/fstab

echo "none /var/mysql_tmpfs tmpfs defaults,size=16g 1 2" >> /etc/fstab

STEP04) Reload /etc/fstab

mount -a

STEP05) service mysql restart

After this, all temp table that become MyISAM are written to the RAM Disk. This should speed disk-based temp table creation.

Give it a Try !!!

Looking at the my.ini, I have two suggestions

SUGGESTION #1

I would bump up the following settings in your my.ini

sort_buffer_size=4M
join_buffer_size=4M

This will make some joins and sort stay in memory. Of course, once a JOIN or an ORDER BY needs more than 4M, it will page to disk as a MyISAM table.

If you cannot login as root@localhost, then restart mysql with

C:\> net stop mysql
C:\> net start mysql

If you can login as root@localhost, you do not have to restart mysql to use these settings.

Just run this in the MySQL client:

SET @FourMegs = 1024 * 1024 * 4;
SET GLOBAL sort_buffer_size = @FourMegs;
SET GLOBAL join_buffer_size = @FourMegs;

SUGGESTION #2

Since your Data is on Drive D:, you may have Disk I/O on Drive C:.

Please run this query:

mysql> show variables like 'tmpdir';
+---------------+-----------------+
| Variable_name | Value           |
+---------------+-----------------+
| tmpdir        | C:\Windows\TEMP |
+---------------+-----------------+
1 row in set (0.00 sec)

Since I run mysql on my Desktop with defaults, my temp tables are being written to Drive C:. If Drive D is a better disk than Drive C:, perhaps you can map temp tables to Drive D: by setting tmpdir in my.ini as follows:

tmpdir="D:/DBs/"

You will have to restart mysql since tmpdir is not a dynamic variable.

Give it a Try !!!

UPDATE 2013-11-29 10:09 EST

SUGGESTION #3

Given the fact that MySQL is running in Windows and you cannot touch the queries in the core package, I have two ideas tat must be done together.

IDEA #1 : Move the Database to a Linux Machine

You should be able to

• Setup a Linux machine
• Install MySQL on the Linux machine
• Enable Binary Logging for MySQL in Windows
• mysqldump the database to a text SQL file
• Load SQL file to MySQL running in Linux
• Setup replication from MySQL/Windows to MySQL/Linux

IDEA #2 : Reconfigure Moodle to point to the Linux Machine

Moodle was designed for LAMP in the first place. Just change the config files to point to the Linux machine instead of localhost.

Here is a link to an old Moodle 2.3 doc on setting up MySQL : http://docs.moodle.org/23/en/Installing_Moodle#Create_an_empty_database

I am sure the latest docs are available as well.

What is the Point of Moving the Database to Linux ???

How does this help the temp table situation ???

I would then suggestion setting up a RAM disk as the target folder for your temp tables

• Jan 04, 2013 : Is there a MySQL engine or trick to avoid writing so many temp tables to disk?
• Dec 17, 2012 : Why does MySQL produce so many temporary MYD files? (Actual instructions)
• Nov 30, 2012 : Is it bad to create many mysql temporary tables simultaneously?

Temp table creation will still happen, but it will be written to RAM rather than disk. reducing Disk I/O.

UPDATE 2013-11-29 11:24 EST

SUGGESTION #4

I would suggest revisiting SUGGESTION #2 with a fast RAID-0 disk (32+ GB), configuring it as Drive T: (T for Temp). After installing such a disk, add this to my.ini:

[mysqld]
tmpdir="T:\"

MySQL restart would be required, using

net stop mysql
net start mysql

BTW I said RAID-0 on purpose so that you can get good write performance over a RAID-1, RAID-10. A tmp table disk is not something I would make redundant.

Without optimizing the queries as @RaymondNijland has been commenting on, you cannot reduce the temp table creation count in any way. SUGGESTION #3 and SUGGESTION #4 offer speeding up temp table creation and temp table I/O as the only alternative.