Error 28, how to avoid it.

What is error 28 and how can I avoid it?

Using the command line tool perror you can find out, what the error 28 means.

> perror 28
Error code 28: No space left on device

If you get his error, you need to check all filesystems where MySQL operates. It may be single filesystem or as we recommend you can have datadir, tmpdir and log files split into dedicated filesystems. MySQL often creates temporary tables for some queries - most of them are placed in tmpdir, but some into database directory (e.g. ALTER TABLE). You must ensure, that there is enough free disk space available for MySQL.

You can check out, that environment variables for MySQL are properly set.

Check the value of tmp_table_size:

mysql> show variables like "tmp_table_size";
+----------------+----------+
| Variable_name | Value |
+----------------+----------+
| tmp_table_size | 33554432 |
+----------------+----------+

This tells, what is the limit, when reached, in-memory temporary tables will automatically be converted to a disk-based MyISAM table.

Then you need to find out, where the 'tmpdir' points

mysql> show variables like "tmpdir";
+---------------+-------------+
| Variable_name | Value |
+---------------+-------------+
| tmpdir | /tmp/mysql/ |
+---------------+-------------+

And check, that there is plenty of space available in that device.