Optimizing MySQL To Let People Argue
Jeremy Bingham, OSCON 2011
Working With What You’re Given, or, “The Legacy
Tables”
Working With What You’re Given, or, “The Legacy
Tables”
• Lots of things that work on a small scale fall apart with millions of
pages a day.
Working With What You’re Given, or, “The Legacy
Tables”
• Lots of things that work on a small scale fall apart with millions of
pages a day.
• Just identify the problems!
Working With What You’re Given, or, “The Legacy
Tables”
• Lots of things that work on a small scale fall apart with millions of
pages a day.
• Just identify the problems! Simple, right?
Working With What You’re Given, or, “The Legacy
Tables”
• Lots of things that work on a small scale fall apart with millions of
pages a day.
• Just identify the problems! Simple, right?
• Improvements possible, but you do have to look back.
Real Tables, Real Problems
Real Tables, Real Problems
• Look for bad indexes.
– Stories used a 20 byte VARCHAR as a primary key.
– Comments used a 20 byte VARCHAR + an integer as a primary key.
– Converted both to use integers.
– Had to keep the old indexes around, of course.
Real Tables, Real Problems
• This will sound really dumb…
Real Tables, Real Problems
• This will sound really dumb…
• … check the indexes are actually there. For some reason, no one
ever bothered to add an index on nicknames on the user table.
The Three Tools I’ve Used Most
EXPLAIN
• Probably the single most useful tool at your disposal
Slow Query Log
• If something’s in there a bunch of times, it’s probably a sign.
SHOW PROCESSLIST;
• And its brother, SHOW FULL PROCESSLIST;
• Can be deceptive; sometimes what seem to be problem queries
are actually fine, but are binding up because of some other query.
EXPLAIN helps here.
Upgrade?
Pros of Upgrading
• New features
• Get beyond limitations of previous versions
– We were held back by a lot of MySQL 3.23isms
Cons of Upgrading
Cons of Upgrading
• Something can go horribly wrong.
Cons of Upgrading
• Something can go horribly wrong.
• Like your data corrupting itself randomly after the upgrade.
Configuration
Let us configure our servers in accordance
with the MySQL lifestyle.
Configuration tricks we’ve used
• Turn off XA transactions
• innodb_flush_log_at_trx_commit =
0
• Per table InnoDB files
• Large Pages
• Work those buffer pool settings
according to your procs and RAM.
• Actually read the docs, and don’t
just go off the ancient sample
configs.
• They leave out a lot of options, or
leave in deprecated ones.
• They’re in Sumerian anyway.
Flog the Hardware
• 2008
– Master/slave 16GB RAM 8 core with dedicated /tmp, 6x73GB RAID 10,
tuned XFS
• 2010
– Master/slave 32GB RAM, quad core, SSD
Election Season
Or, my Christmas comes every two years, but
lasts between six and ten months.
Each cycle builds on the last, but is special and
unique
Taking Opportunities
Redesigning everything and trying to get it
right, but still making sure old stuff works.
Using What I’ve Learned
• Cracking tables apart
• Judicious partitioning
– Where applicable, anyway
– You’ll need lots of experimentation and thought with MySQL’s partitioning
• Ferret out poorly thought out primary keys
Using What I’ve Learned
•
•
•
•
•
Trim out truly unneeded columns and tables
Move less used columns off to the side
Better foreign keys and join tables
Stat tables, to avoid certain painful queries
Lots of testing with a full copy of the data
The Most Important Thing
• Cache, cache, cache!
• Cache pages to disk
– Great in 2006, blew up horribly during the Iowa caucuses in 2008
• Started storing pages in memcached for anonymous users in
2008
More Caching
• Cache fragments and collections for logged in folks too.
• Particularly intense queries can be run from a cron so they’re
always available.
• Slower updates can be kicked to a background daemon.
Caching’s Terrible Downside
Never underestimate how much people will gripe if something’s not
exactly up to date. Somehow, they’ll notice.
What in God’s name was I thinking?
Jeremy Bingham
[email protected]
Twitter: @captain_tenille
http://time.to.pullthepl.ug
Photo Credits:
–Siegfried, public Domain
–PDP-10, Michael L. Umbricht
–Stone axe, Didier Descouens
–Hammer, Evan-Amos
–Adze, Luigi Zanasi
–Teamsters strike in 1934, US Government work
Questions?