- global transaction IDs
- batch key access
- much better SMP performance for SHOW USER_STATS
- more changes to improve SMP performance. Changes were made to reduce contention on log_sys->mutex and buffer_pool->mutex.
- checksums on binlog events
Update 1 -- Domas asked about the overhead from using crc32 rather than adler32 for checksums. I did not measure any difference. Using checksums reduces performance by 3% to 7%. Details on the change and performance results are here.
Update 2 -- the latest SMP changes by Ben Handy improve sysbench readwrite performance by 20% at high levels of concurrency. My results are here.
Update 3 -- we backported batch key access from MySQL 6. Details are here.