Restoring Large Number of MySQL Databases

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We have a large number of databases:
more than 250,000 tables (660 databases, 60 Gb).

Restoring a single database was a good time to restoring.
When restoring all databases at once, the process takes too much time: 8 hours restoring and it still didn't finish.

{kb-cause}

When databases are restored individually, the process naturally takes long time. The reason is that each row must be selected and inserted.

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