This is mostly performance improvement release, however, it primarily affects regular sync time (fast sync is as fast as before). So here are improvements:

• Since ref counting DB introduction the DB write performance significantly dropped, so there are changes to compensate this drawback
  • Asynchronous background write cache flush: the flush is now performed in background thread and almost doesn't affect the blocks import speed
  • DB Bloom filters: updating the Trie in ref counting DB is significantly slowed down by inserting new nodes and deleting pruned nodes: each operation requires additional DB read to get current ref count. We added two bloom filters: the first is filtering non-existing node entries (speeds up insert-if-absent operation), the second is filtering node with ref count < 2 (speeds up delete operation)
• New Trie implementation with optimized updates and root calculation gave us up to x20 speed up on some scenarios due to parallelization
• Program precompiles DB cache improves performance in general and especially on some attack blocks
• Eliminate 'hot' prototype Spring beans where Spring machinery overhead became a problem
• Genesis config support allows specifying blockchain parameters (like fork blocks, chainId, etc) in Genesis config section
• Latest Solidity new features support like function types and payable flag
• Flush all DB changes with a single LevelDB batchUpdate should increase DB reliability
• Get rid of the last MapDB dependency: now all the data is stored with LevelDB only
• And of course, bugs fixing and new bugs creation
• NOTE: DB structure (databaseVersion) was changed so after upgrade your node will be forced to sync from scratch