I would like to create a backup of different MyISAM tables on a server using mysqlhotcopy. These tables are about 6GB in size. I would like to know, does mysqlhotcopy block users from SELECTing (reading) data from the tables while taking the backup?
Thanks in advance, Tim
The documentation is not as clear as it should be, but I would say no, mysqlhotcopy does not block SELECT queries.
Here is why
mysqlhotcopy is a Perl script that was originally written and contributed by Tim Bunce. It uses FLUSH TABLES, LOCK TABLES, and cp or scp to make a database backup. It is a fast way to make a backup of the database or single tables, but it can be run only on the same machine where the database directories are located. mysqlhotcopy works only for backing up MyISAM and ARCHIVE tables. It runs on Unix and NetWare.
To use mysqlhotcopy, you must have read access to the files for the tables that you are backing up, the SELECT privilege for those tables, the RELOAD privilege (to be able to execute FLUSH TABLES), and the LOCK TABLES privilege (to be able to lock the tables).
• If you are using tables for a nontransactional storage engine, you must use LOCK TABLES if you want to ensure that no other session modifies the tables between a SELECT and an UPDATE. The example shown here requires LOCK TABLES to execute safely: LOCK TABLES trans READ, customer WRITE; SELECT SUM(value) FROM trans WHERE customer_id=some_id; UPDATE customer SET total_value=sum_from_previous_statement WHERE customer_id=some_id; UNLOCK TABLES; Without LOCK TABLES, it is possible that another session might insert a new row in the trans table between execution of the SELECT and UPDATE statements.
In summary, since mysqlhotcopy launches LOCK TABLES, SELECT queries are evidently still allowed.
I you definitely don't want to block the user from any action, set up a replication slave. You can hotcopy those tables without impacting on the end user.
