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Re: Slow inserts/restore from backup
Posted by: Michal Koscielny
Date: January 02, 2019 07:31AM

I experience the same problem on Windows 10. I have a fairly small database dump from mysql 5.7 of size 538 MB, created with mysqldump, most of the tables are InnoDB and the dump uses bulk inserts (default). Restoring the dump to 5.7 takes 5 minutes 35 seconds, while restoring to 8.0.13 takes 23 minutes 4 seconds. This is a huge difference.

I'm using a sata SSD drive and I've noticed very high CPU usage during mysql 8 restore - mysqld.exe process consumes 80-90% of CPU all the time whereas disk writes are quite slow at around 10MB/s. So the restore process speed is definitely CPU bound.

When restoring to mysql 5.7 the CPU utilization is much less - around 25% and disk writes are much faster.

I've also tried disabling binary logging but it made not much difference.

Does anyone know what causes high CPU during dump restore? I can't find any settings to resolve the issue. I suppose inserts are simply much slower in mysql 8.0.x.

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