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Whilst this does not affect the initial execution of the SQL query (20 seconds), it does make subsequent executions for the same profile faster - approximately 14 seconds. It may be that innodb_buffer_pool_size is the main reason for the performance boost - having a sufficiently large buffer pool means that InnoDB can generate in-memory adaptive hash indexes. Hash indexes (which are only available in memory) are far more efficient for the types of joins that SDB is doing, which are all based on hash values anyway.
The InnoDB buffer pool can be pre-loaded at startup, which would help the initial query performance times - see: https://dev.mysql.com/doc/refman/5.7/en/innodb-preload-buffer-pool.html
It's not known what size buffers should really be used for any given database size, or how well this translates into overall performance, e.g. how much can be cached to the benefit of the entire application. Of course, each individual site would need to look at the resources available on their own systems, and what they can dedicate to a given purpose.
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