Database Tuning By Tim Messer

Agenda Brief overview of tuning General tuning techniques Theory behind tuning Lots of silly looking dogs

Agenda Brief overview of tuning General tuning techniques Theory behind tuning Lots of silly looking dogs

What is tuning? Tuning is optimizing a database for a specific purpose. Often overlooked. Can offer serious performance boosts.

What is tuning? Can offer serious performance boosts. Something bad becomes passable.

What is tuning? Can offer serious performance boosts. Something good becomes something great.

Tuning Theory Consider all aspects of the system. Remember that your database is just one part of a larger whole piece of software, on a network of hardware. A few of the many things you can (and should) check when tuning: System downtimes Batch job failures Resource utilization history Update history Partner machine needs and stability (apps servers, etc)

Priority list for tuning Hardware stability No computers are crashing often. The network cables and routers are reliable. Hardware adequacy Hardware on all machines is appropriate. No ancient Pentium I processors holding everyone up. Operating System and so forth is up to date. Software design Database tables work well for application. Software utilization Software doesn't have outrageous demands being made of it (bad SQL).

Hardware Clearly the most important part. No amount of tuning can compensate for bad hardware. =

Hardware Give your DB a good home before starting. =

General Tuning Techniques Keep table size down. On particularly large databases undergoing large queries, going from the hard drive to RAM and RAM to CPU can be very taxing. A good rule of thumb: Think of single tables in terms of seconds of motherboard capacity.

This part's important don't look away now Example table calculation: Data deliveries per second * size of deliveries = throughput Motherboard: Intel 3010, 1066MHz FSB CPU. Front Side Bus (FSB): 1066 MHz, 32 bit. ((FSB Speed*1000) * Bit width) = throughput (in bits) Throughput/(1,048,576 * 8) = throughput (in MB) (1,066,000 * 32)/(1,048,576 * 8) = 2.56 MB So a 25 MB table is a 10-second table. A 5MB one is a 2-second table.

Seriously this part's useful How long is too long? This entirely depends on what the database is doing. To get a reply out of a 10-second table, you will need up to 10 seconds to get a result. Honestly ask yourself: Is that going to annoy people? Some considerations for annoyance How often is this table used per day? Who uses it? What else is going on while it's being used?

Table size How to cut size down directly? Archive old stuff Divide tables up more finely (one table per user instead of a big users table) Eliminate redundant stuff Kind of like grooming a dog.

Table size Kind of like grooming a dog. (Cannot be the only thing you do. The real world is wet tar to your database.) +

RESULT

General Tuning Techniques Add better indexes and reference tables Indexes allow searches to immediately ignore data that is clearly not what its looking for. Reference tables allow quick lookups.

Indexes Indexes are no different in theory from the index in the back of a book. When looking for a single String1 = String2 comparison, it checks the first letter, then the second, and so on. Instead of looking at all records, you look at only records which sort of fitlooks like a tree structure. Normal searches are linear, and require as many operations as the table has records. Indexed searches are much more efficient, and require log(records) time. All modern databases HAVE indexesthey are not always properly used, however.

Indexes This ignored area is commonly hundreds of thousands of rows.

Reference table example Example of reference table use: Imagine an e-commerce website with keywords on items.

Reference Table Example Imagine we must find products based on these keywords. Assume 100,000 individual entries to the Product table, with an average of 3 five letter keywords each. Search for ONE keyword. First option: Search the keywords field. Obscenely slow. Requires as many operations as the string is long; string length 5 requires 5 operations, length 10 requires 10, etc. Called linear(n) time with respect to string length. 17 length keyword field * 100,000 records = 1.7 million operations for 1 search. …many customers looking at the same time, too.

Reference Table Example Option 2: make reference tables by keyword Create Table electronics, and put anything with electronics in the keyword field in there. Can be done while system is otherwise idle. Middleware can make new tables for new keywords automatically. Requires only 1 operation to finish. Select * from (keyword). Called Constant time. This is how Google returns millions of webpages in a fraction of a second.

Reference Table Example This search would have taken years on the best supercomputers in the world if simple text searches were done.

Reference Tables and Interfaces What does this do for you? This makes the computer look at less useless stuff when searching for something. Resists huge and sudden increases in size and subsequent drops in speed. Doesn't address underlying problems.

General Tuning Technique Doesn't address underlying problems +

RESULT

General Tuning Techniques Check the SQL being fed into the database. All current databases keep logs of what SQL they run. Bad SQL can potentially hurt performance much more than big tables or clunky interfaces. Call up an audit and see if anything stands out as particularly slow or taxing. Rewrite it if possible.

SQL Monitoring What does this do for you? Keeps people from doing too many dumb things, which they will despite your best efforts. Again doesn't address any real problems with the DB.

Monitoring tools SQL Power Tools ( Monitors a database remotely, giving no overhead. Puts things into graph form. Can monitor entire server farms (up to 250). Web-enabled interface. $1200. Freeware monitoring tools are few, far in between, and usually pretty primative. Mostly, they involve individual developers writing frontends for already-existing feedback programs like netstat and adding in alarms and so forth. Hard to find online. Most freeware programs you can find have serious flaws.

Monitoring Tools SQL Monitor: ( monitor.html ) Freeware Only does SQL testing very well. SQLXML 3.0 ( Comes free with Microsoft SQL Server. Very useful in getting database schema into XML for presentation. Only works with MSSQL (very common problem!)

And many more There are dozens and dozens of techniques to tune a database. Parallelism (setting up multiple computers to serve a single DB), indexing, and caching are just a few words that would work for all DBs...then there are dozens more specifically for Oracle, mySQL, MSSQL, and so forth. Reading and asking informed questions is key! There is no one procedure or good answer to a well tuned database.

Sources O'Reilly Databases, RDBMS Tuning. Steven Hauser. University of Arkansas, Oracle Database Tuning. Steve Rea. Database Tuning: Principles, Experiments, and Troubleshooting Techniques. Dennis Shasha and Philippe Bonnet. (Paperback version: Troubleshooting/dp/ Special Thanks to: Google, for endless pictures of silly dogs. Nikita Minter, for the Party Doog picture.