quick start/stop with innodb_buffer_pool_dump_pct < 100 results in suboptimal dump file

With innodb_buffer_pool_dump_pct say 25% (the default since 10.2.2), a server started will restore 25% of the buffer pool size with the expectation that over time the rest of the buffer pool will be populated. Then on shutdown 25% will be saved.

If a server is started and then is shutdown a) without much activity occurring b) is started as a hot spare and shutdown before being used, then 6.25% (25% of 25%) of the buffer pool is saved.

Proposed solution:

Rather than innodb_buffer_pool_dump_pct referring to the percentage of hot data in the buffer pool, it refers to the entire buffer pool size. This means that a completed load followed by a shutdown will write the exact same data.

This will generate bigger dump files for users who don't have a full innodb_buffer_pool however a realistic scenario is a buffer pool should be completely used.