Morgan Tocker from Oracle gave a good overview of what is new in MySQL 8.0.  Notes:

• 5.7 improvements
  • Group Replication
  • Performance Schema
  • SYS Schema
  • JSON Support
  • Performance
  • Partitions
  • Trigger Changes
  • MAIN changes
    • GIS support
    • JSON Types
    • Observational Management
• Premium placed on Time to Market in modern applications
• MysQL 8
  • GIS
    • Spatial Reference System (SRS) Support
    • Helper functions to manipulate and convert data
      • st_x
      • st_y
      • st_srid
  • JSON
    • a bunch of new functions
    • example showing how to query JSON data out of a JSON doc stored in a column
  • utf8mb4 now default (UNICODE 9)
    •  a lot already were using as default
    • emojis
    • new collations
      • Japanese and Russian
  • Performance
    • showed sysbench read only performance improvements
    • utfmb3 and utfmb4
      • 4 byte more performant so they are deprecating the 3 byte
  • UUID
    • ability to convert to bin and back
    • binary format reorders pieces of the UUID to allow them to follow insert order to avoid splits
  • Hot Row contention handling
    • NOWAIT – Error immediately
    • SKIP LOCKED – only operate on non locked rows (non deterministic)
  • Common Table Expressions
    • WITH t1 AS (SELECT * FROM tblA WHERE a=’b’) SELECT * FROM t1;
    • optimizer know if it needs to use temp table sor if it just needs to rewrite the query on its end
    • Recursive CTEs also supported
  • Analytics Queries with Windows Functions
    • PARTITION BY
  • Optimizer improvements
    • considers how much of an index is in memory vs. on disk
    • Range Scans will be used if all data is in memory
    • can see in info schema how much is in memory (estimated by InnoDB)
    • Histograms support
      • lower cost alternative to an index
      • created on demand and updated manually
      • no regular overhead until told to re-update
      • 2 types
        • equi-height
        • singleton
    • Descending indexes
    • Invisible Indexes (Hidden indexes)
      • Soft deletes
      • Staged Rollouts
      • Still maintained even if not visible
      • only a metadata change to switch visible vs invisible
    • Performance Schema
      • A lot more instrumentation
      • improved defaults so things are on
        • memory
        • transactions
        • metadata – all three on by default in MySQL 8
      • Better indexing on the performance schema – improved performance of querying this data
      • Now can see errors returned to clients from within performance schema
      • Added histograms in addition to min max average to show distribution better (write CTE to visualize)
        • per statement digest basis
      • Window into InnoDB locks – row locks
      • see where variables are sourced from (configuration variables)
    • Information Schema
      • a lot of tables are migrated to views on top of mysql tables to improve performance
      • 30 times faster
    • Consistent Configuration
      • json file that allows you to persist changes to configuration from commands in the instance
    • Crash safe data dictionary
    • New defaults
      • utf8md4
      • new collation
      • performance schema – memory, transactions, MDL on by default
      • InnoDB –
    • Some replication changes
    • Can “set persist_only innodb_dedicated_server = true” – resets settings as systems are sized up and down