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When you run mysqladmin status
, you'll see something like this:
Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12 |
The Open tables
value of 12 can be somewhat puzzling if you have
only 6 tables.
MySQL is multi-threaded, so there may be many clients issuing queries for a
given
simultaneously. To minimise the problem with two client threads having
different states on the same file, the table is opened independently by
each concurrent thread. This takes some memory but will normally increase
performance. With ISAM
and MyISAM
tables,
one extra file descriptor is required for the datafile for each client that
has the table open. With these table types, the index
file descriptor is shared between all threads.
You can read more about this topic in the next section. See section 7.4.8 How MySQL Opens and Closes Tables.