I downloaded the book, and the size can be reduced slightly with pdfsizeopt.

I don't have any of the extended filters, but it is a small size reduction with the default load:

  $ ./pdfsizeopt next-level-database-techniques-for-developers.pdf
  ...
  info: generated object stream of 7399 bytes in 224 objects (9%)
  info: generated 387518 bytes (89%)

  $ stat -c '%s %n' next*.pdf
  435483 next-level-database-techniques-for-developers.pdf
  387518 next-level-database-techniques-for-developers.pso.pdf