When you run mysqladmin status you get something like:
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12
This can be somewhat perplexing if you only have 6 tables.
As MySQL is multithreaded it may have many queries on the same table at once. To minimise the problem with two threads having different states on the same file, I open the table again for each concurrent thread. This takes some memory and one extra file descriptor for the data file. The index file descriptor is shared between all threads.
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