Summary of changes in MySQL 5.6

MySQL databaseWell, this is just a forwarded version from, the highlighted points are a good summary. I don’t fully understands all the germs till now. The manual page is  worth a careful read if you want to know more details.

The original post is as below:

  • InnoDB: supports fulltext search; more kinds of ALTER TABLE avoid copying/rebuilding the table, some without blocking the table at all (truly online ALTER TABLE); more flexibility with data files; improvements to compression; improvements to flushing to avoid checkpointing stalls; ability to access InnoDB tables through the memcached protocol instead of SQL; more INFORMATION_SCHEMA tables; persistent optimizer statistics that can be stored in tables, viewed and manipulated; performance optimizations for readonly transactions; ability to put the undo log into its own file instead of the main tablespace; bigger redo logs; limits on data dictionary size when there are many tables; a lot of work on mutex contention problems; many changes to internal housekeeping threads; faster deadlock detection algorithm; automatic save/restore of buffer pool state for faster warmup;  tables can be exported and imported between servers without dump/load.
  • Partitioning: you can promote a partition into a table and vice-versa; you can limit queries to touch only desired partitions.
  • Performance Schema: many helpful new tables including statement digests; much lower performance penalty; more configurable both at runtime and in the my.cnf file.
  • Replication: RBR can use a more compact format; binary logs are crash-safe; binary logging supports group commit, for much faster performance in the configuration most people use when they care about their data; binlog events have CRC32 checksums to prevent corruption; master- and slave- position are stored in tables as well as files; replication position can now be transactional if that table is InnoDB, so replication is more resilient; mysqlbinlog can connect to a server and stream an exact copy of its binlogs, so you can have realtime binlog backups without needing to use a slave; you can delay replication (no more pt-slave-delay); replication slaves are multi-threaded so that transactions are replayed in per-database threads.
  • Optimizer: SELECT..ORDER BY..LIMIT uses a memory buffer instead of a temp table + filesort when there is no index; queries can use a couple of strategies kind of like a sort-merge operation to reduce random IO; WHERE clauses can be pushed into the storage engine and avoid reading a ton of data and then discarding it; the “leftmost prefix rule” for indexes is lifted, so “loose index scan” is possible; EXPLAIN works for all kinds of statements, not just SELECT; “derived table” subqueries aren’t materialized into temp tables unless needed, and EXPLAIN doesn’t create and fill them, and the optimizer adds indexes to help optimize JOINs against them; IN(SELECT…) subqueries are executed inside-out, so they aren’t a table scan anymore; there is an optimizer trace so you can get a super-detailed EXPLAIN.
  • Stored procedures: Better error inspection and handling.
  • Data types: microsecond precision for time types; more flexible DEFAULT instead of the automatic “timestamp” behavior (it works for datetime now too), YEAR(2) data type is deprecated.
  • Host cache: it’s now exposed as a table, and there are more metrics for inspecting it.
  • Removed features: some logging options; some old variable names; some old MyISAM features like INSERT DELAYED.
  • Table cache: the table cache is partitioned for improved performance.
  • Security: more convenient ways to keep passwords safe when using client programs; stronger password hashing; password expiration; ability to check passwords for security/policies
  • Misc: a bunch of new status counters.
  • Many more changes I’ve overlooked or didn’t mention.

Have fun!

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