Comments - what is the difference between MariaDB and Oracle?
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Answering on the 2nd part:
Blackhole was originally a minimal example to show how the storage engine API can be used to implement new storage engine, with its only practical use was to be used in benchmarks to measure the query handling / SQL parsing performance without actually really performing any data operations.
Later it also got used in certain replication setups where intermediate slaves are needed to perform different filter operations on the binlog files generated by a replication master, e.g. when having a central master maintaining data for several sites, but each site only wanting to have one certain schema / database and being behind a slow link (modem, ISDN, ...) so that client side filtering isn't an option. In this case you can set up multiple intermediate slaves on the master side with the sole purpose of applying "binlog-do/binlog-ignore" filters on the master replication stream and then writing a filtered replication binlog that a remote site slave can replicate from. This requires one intermediate slave per remote site, but the intermediate slave doesn't actually need to store any data, so forcing these intermediate "dummy" filter instances to use BLACKHOLE takes away data storage overhead that wouldn't be needed here anyway.