mysql - How To Avoid Repair With Keycache?

Question

I have had some experience with optimizing the my.cnf file but my database has around 4 million records (MyISAM). I am trying to restore from a mysqldump but every time I do I eventually get the dreaded "Repair With Keycache", that may take days. Is there any way to get past this and let it roll as "Repair By Sorting"?

I have 2GB RAM, Dual Cores, lots of extra hard-drive space.

Snip out of my.cnf:

set-variable = max_connections=650
set-variable = key_buffer=256M
set-variable = myisam_sort_buffer_size=64M
set-variable = join_buffer=1M
set-variable = record_buffer=1M
set-variable = sort_buffer_size=2M
set-variable = read_buffer_size=2M
set-variable = query_cache_size=32M
set-variable = table_cache=1024
set-variable = thread_cache_size=256
set-variable = wait_timeout=7200
set-variable = connect_timeout=10
set-variable = max_allowed_packet=16M
set-variable = max_connect_errors=10
set-variable = thread_concurrency=8

Answer 1

"Repair by sorting" uses the filesort routine, which in turn creates several temporary files (usually) in your tmpdir.

If your tmpdir does not have enough space for them, it will revert to "Repair by keycache". This is extremely bad as it's much slower AND creates less optimal indexes.

There are some other conditions but I haven't identified them.

Working out the size of tmpdir you need for filesort() is nontrivial; the format data are stored in the filesort buffer is not the same as MYD files, it typically uses a lot more space.

So if your tmpdir points at a small /tmp (or tmpfs), you might want to change it to a larger /var/tmp - if that exists.