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This is the 182nd edition of Log Buffer, the weekly review of database blogs. Make sure to read the whole edition so you do not miss where to submit your SQL limerick!

This week started out with me posting about International Women’s Day, and has me personally attending Confoo (Montreal) which is an excellent conference I hope to return to next year. I learned a lot from confoo, especially the blending nosql and sql session I attended.

This week was also the Hotsos Symposium. Doug’s Oracle Blog has a series of posts about Hotsos. If all this talk about conferences has gotten you excited, Joshua Drake notes that 14 days and the hotel is almost full for postgresql conference east which is March 25th-28th in Philadelphia. And the Oracle database insider notes that the Oracle OpenWorld call for papers is now open.

According to Susan Visser this week (ending tomorrow) is also read an e-book week. So if you have not already done so, read an e-book! She links a coupon for an e-book in the post.

Craig Mullins notes that the mainframe is a good career choice in Mainframes: The Safe IT Career Choice. He notes that the mainframe is still not dead:

People having been predicting the death of the mainframe since the advent of client/server in the late 1980s. That is more than 20 years! Think of all the things that have died in that timespan while the mainframe keeps on chugging away: IBM’s PC business, Circuit City, Koogle peanut butter, public pay phones, Johnny Cash… the list is endless.

In other career-related news, Antonio Cangiano is looking for [2] top-notch student hackers for a 16-month internship at IBM in Toronto starting in May. All the details, including how to apply, are in Cangiano’s blog post.

Willie Favero wants to know how you “solve the batch dilemma” for issues like “shrinking your batch window, designing your batch to play nicely with … OLTP” in how’s your batch workload doing? Perhaps Favero should read the updated batch best practices posted by Anthony Shorten.

Bryan Smith surveys a more personal question by asking if you go both ways and “manage both DB2 for Linux, UNIX, and Windows and DB2 for z/OS” in don’t ask, don’t tell, bi-platform DBAs. This week’s Log Buffer editor admits to being a tri-platform DBA — she has tried many platforms, and in fact, many databases (MySQL, Oracle, DB2, SQL Server, Sybase, Postgres and Ingres)!

Hari Prasanna Srinivasan promotes a patching survey in Oracle really wants to hear from you! Patching Survey.

Henrik Loeser explains what a deadlock and a hot spot are by using a real life analogy taken from a police report in deadlock and hot spot in real life.

Jamie Thomson asks why do you abbreviate schema names?. Shlomi Noach tries to solve the issue that “there is no consistent convention as for how to write [about table aliases in] an SQL query” in proper sql table alias use conventions. Noach also gives us a tip: faster than truncate.

Leons Petrazickis reminds us that “rulesets are chains” and it is important to have your rulesets in the proper order in iptables firewall pitfall.

Anyone interested in the history of MySQL AB will be informed after reading Dries Buytaert’s article.
Gavin Towey shares his software that helps centrally manage 120 MySQL servers in qsh.pl: distributed query tool For those who want to learn more about column-oriented databases, particularly in MySQL, Robin Schumacher of the InfiniDB blog announces that there is a MySQL University session recording on MySQL column databases now available. MySQL join-fu expert Jay Pipes has moved his blog to www.joinfu.com and starts with An SQL Puzzle and of course a follow up on the sql puzzle.

Ivan Zoratti is happy that finally, slides posted for the MySQL DW breakfast. Venu Anuganti gives you tips on one of the most common MySQL frustrations: optimizing subqueries in how to improve subqueries derived tables performance. Justin Swanhart posts the way in which he Gets Linux performance information from your MySQL database without shell access and emulates a ‘top’ CPU summary using /proc/stat and MySQL using the same method.

The Oracle Apps blog has an introduction to Oracle user productivity kit (UPK). Even though in this editor’s opinion the article is very sales-pitchy, it has valuable information, and does indeed live up to its promise:

UPK is a software tool that can capture all the steps in a system process. It records every keystroke, every click of the mouse, each menu option chosen and each button pressed. All this is done in the UPK Recorder by going through the transaction and pressing “printscreen” after every user action. From this, without any further effort from the developer, UPK builds a number of valuable outputs.

Allen White gives a great tip on how to optimize queries in keep your data clean.

Mike Dietrich reminds you to remove “old” parameters and events from your init.ora when upgrading, “as keeping them will definitely slow down the database performance in the new release.” He shows evidence of slowness when this is not done. Dietrich also shows how you can be gathering workload statistics “to give the optimizer some good knowledge about how powerful your IO-system might be”, especially “a few days after upgrading to the new release…while a real workload is running.”

Brian Aker shows the exciting features coming soon in Drizzle in Drizzle, Cherry, Roadmap for our Next Release.

Maybe you are thinking of migrating, not upgrading…..The O’Reilly Radar shows how to asses an Oracle to MySQL migration in MySQL migration and risk management. Actually, that article interviews Ronald Bradford on the subject — Bradford has been prolific lately, updating free my.cnf advice series and “Don’t Assume”: MySQL for the Oracle DBA series. Nick Quarmby also talks about migrating Oracle, but not to a new database, just to a new platform, in his primer on migrating Oracle Applications to new platforms. And the big news comes from Carlos of dataprix that Twitter will migrate from MySQL to Cassandra DB.

Paul S. Randal explains his way of benchmarking: 1 Tb table population on SQL Server.

Pete Finnigan shares his slides from a webinar on how to secure oracle, and Denis Pilipchuk shares his approaches for discovering security vulnerabilities in software applications.

Jeff Davis shares his thoughts about scalability and the relational model. Robert Treat responds actually, the relational model doesn’t scale and Baron Schwartz counters with NoSQL doesn’t mean non-relational.

Buck Woody explains “whenever you want to know something about SQL Server’s configuration, whether that’s the Instance itself or a database, you have a few options” — and of course what those options are — in system variables, stored procedures or functions for meta data.

This week’s T-SQL Tuesday topic was I/O. There are many links to great blog posts in the comments; three random posts I chose to highlight: Michael Zilberstein talks about IO capacity planning, while Kalen Delaney talks about using STATISTICS IO in I/O, you know, and Merrill Aldrich chimes in with information on real world SSD’s. Aldrich also begs folks not to waste resources and make more work for developers and DBAs in dear ISV, you’re keeping me awake nights with your VARCHAR() dates.

And we end with a bit of fin: Paul Nielsen wants us all to have a bit of fun; he has posted an SQL limerick and asks readers to create there own in there once was in Dublin a query.

PlanetMySQL Voting: Vote UP / Vote DOWN

Persistence Smoothie: Blending NoSQL and SQL – see user feedback and comments at http://joind.in/talk/view/1332.

Michael Bleigh from Intridea, high-end Ruby and Ruby on Rails consultants, build apps from start to finish, making it scalable. He’s written a lot of stuff, available at http://github.com/intridea. @mbleigh on twitter

NoSQL is a new way to think about persistence. Most NoSQL systems are not ACID compliant (Atomicity, Consistency, Isolation, Durability).

Generally, most NoSQL systems have:

• Denormalization
  
• Eventual Consistency
  
• Schema-Free
  
• Horizontal Scale
  

NoSQL tries to scale (more) simply, it is starting to go mainstream – NY Times, BBC, SourceForge, Digg, Sony, ShopWiki, Meebo, and more. But it’s not *entirely* mainstream, it’s still hard to sell due to compliance and other reasons.

NoSQL has gotten very popular, lots of blog posts about them, but they reach this hype peak and obviously it can’t do everything.

“NoSQL is a (growing) collection of tools, not a new way of life.”

What is NoSQL? Can be several things:

• Key-Value Stores
  
• Document Databases
  
• Column-oriented data stores
  
• Graph Databases
  

Key-Value Stores

memcached is a “big hash in the sky” – it is a key value store. Similarly, NoSQL key-value stores “add to that big hash in the sky” and store to disk.

Speaker’s favorite is Redis because it’s similar to memcached.

• key-value store + datatypes (list, sets, scored sets, soon hashes will be there)
  
• cache-like functions (like expiration)
  
• (Mostly) in-memory
  

Another interesting key-value store is Riak

• Combination of key-value store and document database
  
• heavy into HTTP REST
  
• You can create links between documents, and do “link walking” that you don’t normally get out of a key-value store
  
• built-in Map Reduce
  

Map Reduce:

• Massively parallel way to process large datasets
  
• First you scour data and “map” a new set of dataM
  
• Then you “reduce” the data down to a salient result — for example, map reduce function to make a tag cloud: map function makes an array with a tag name and a count of 1 for each instance of that tag, and the reduce tag goes through that array and counts them…
  
• http://en.wikipedia.org/wiki/MapReduce
  

Other key-value stores:

• Tokyo Cabinet
  
• Dynomite
  
• memcachedDB
  
• Voldemort
  

Document Databases

Some say that it’s the “closest” thing to real SQL.

• MongoDB – Document store that speaks BSON (Binary JSON, which is compact). This is the speaker’s favorite because it has a rich query syntax that makes it close to SQL. Can’t do joins, but can embed objects in other objects, so it’s a tradeoff


• Also has GridFS that can store large files efficiently, can scale to petabytes of data
  
• does have MapReduce but it’s deliberate and you run it every so often.
  
• CouchDB
  
  • Pure JSON Document Store – can query directly with nearly pure javascript (there are auth issues) but it’s an interesting paradigm to be able to run your app almost entirely through javascript.
    
  • HTTP REST interface
    
  • MapReduce only to see items in CouchDB. Incremental MapReduce, every time you add or modify a document, it dynamically changes the functions you’ve written. You can do really powerful queries as easy as you can do simple queries. However, some things are really complex, ie, pagination is almost impossible to do.
    
  • Intelligent Replication – CouchDB is designed to work with offline integration. Could be used instead of SQLite as the HTML5 data store, but you need CouchDB running locally to be doing offline stuff w/CouchDB
    
  
  

Column-oriented store

Columns are stored together (ie, names) instead of rows. Lets you be schema-less because you don’t care about a row’s consistency, you can just add a column to a table very easily.

• Cassandra – Built by Facebook, also used by Twitter
  
• BigTable
  
• Hypertable
  
• HBase
  

Graph Databases

speaker’s opinion – there aren’t enough of these.
Neo4J – can handle modeling complex relationships – “friends of friends of cousins” but it requires a license.

When should I use this stuff?

If you have:	Use
Complex, slow joins for an “activity stream”	Denormalize, use a key-value store.
Variable schema, vertical interaction	Document database or column store
Modeling multi-step relationships (linkedin, friends of friends, etc)	Graph

Don’t look for a single tool that does every job. Use more than one if it’s appropriate, weigh the tradeoffs (ie, don’t have 7 different data stores either!)

NoSQL solves real scalability and data design issues. But financial transactions HAVE to be atomic, so don’t use NoSQL for those.

A good presentation is http://www.slideshare.net/bscofield/the-state-of-nosql.

Using SQL and NoSQL together

Why? Well, your data is already in an SQL database (most likely).

You can blend by hand, but the easy way is DataMapper:
Generic, relational ORM (adapters for many SQL dbs and many NoSQL stores)
Implements Identity Map
Module-based inclusion (instead of extending from a class, you just include into a class).

You can set up multiple data targets (default is MySQL, example sets up MongoDB too).
DataMapper is:

• Ultimate Polyglot ORM
  
• simple r’ships btween persistence engines are easy
  
• jack of all, master none
  
• Sometimes perpetuates false assumptions –
  
• If you’re in Ruby, your legacy stuff is in ActiveRecord, so you’re going to have to rewrite your code anyway.
  

Speaker’s idea to be less generic and better use of features of each data store – Gloo – “Gloo glues together different ORMs by providing relationship proxies.” this software is ALPHA ALPHA ALPHA.

The goal is to be able to define relationships on the terms of any ORM from any class, ORM or not
Right now – partially working activeRecord relationships
Is he doing it wrong? Is it a crazy/stupid idea? Maybe.

Example:

Need	Use
Assume you already have an auth system	it’s already in SQL, so leave it there.
Need users to be able to purchase items from the storefront – Can’t lose transactions, need full ACID compliance	use MySQL.
Social Graph – want to have activity streams and 1-way and 2-way relationships. Need speed, but not consistency	use Redis
Product Listings — selling moves and books, both have different properties, products are pretty much non-relational	use MongoDB

He wrote the example in about 3 hours, so integration of multiple data stores can be done quickly and work.

PlanetMySQL Voting: Vote UP / Vote DOWN

Most of this stuff is not PHP specific, and Python or Ruby or Java or .NET developers can use the tools in this talk.

The session on joind.in, with user comments/feedback, is at http://joind.in/talk/view/1320.

Slides are at http://talks.php.net/show/confoo10

“My name is Rasmus, I’ve been around for a long time. I’ve been doing this web stuff since 1992/1993.”

“Generally performance is not a PHP problem.” Webservers not config’d, no expire headers on images, no favicon.

Tools: Firefox/Firebug extension called YSlow (developed by yahoo) gives you a grade on your site.

Google has developed the Firefox/Firebug pagespeed tool.

Today Rasmus will pick on wordpress. He checks out the code, then uses Siege to do a baseline benchmark — see the slide for the results.

Before you do anything else install an opcode cache like APC. Wordpress really likes this type of caching, see this slide for the results. Set the timezone, to make sure conversions aren’t being done all the time.

Make sure you are cpu-bound, NOT I/O bound. Otherwise, speed up the I/O.

Then strace your webserver processs. There are common config issues that you can spot in your strace code. grep for ENOENT which shows you “No such file or directory” errors.

AllowOverride None to turn off .htaccess for every directory, just read settings once from your config file….(unless you’re an ISP).

Make sure DirectoryIndex is set appropriately, watch your include_path. All this low-hanging fruit has examples on the common config issues slide.

Install pecl/inclued and generate a graph – here is the graph image (I have linked it because you really want to zoom in to the graph…)

In strace output check the open() calls. Conditional includes, function calls that include files, etc. need runtime context before knowing what to open. In the example, every request checks to see if we have the config file, once we have config’d we can get rid of that stuff. Get rid of all the conditionals and hard-code “include wp-config.php”. Examples are on the slide.

His tips to change:
Conditional config include in wp-load.php (as just mentioned)
Conditional did-header check in wp-blog-header.php
Don’t call require_wp_db() from wp-settings.php
Remove conditional require logic from wp_start_object_cache

Then check strace again, now all Rasmus sees is theming and translations, which he decided to keep, because that’s the good benefit of Wordpress – Performance is all about costs vs. flexibility. You don’t want to get rid of all of your flexibility, but you want to be fast.

Set error_reporting(-1) in wp-settings.php to catch all warnings — warnings slow you down, so get rid of all errors. PHP error handling is very slow, so getting rid of errors will make you faster.

The slide of warnings that wordpress throws.

Look at all C-level calls made, using callgrind, which sits under valgrind, a CPU emulator used for debugging. See the image of what callgrind shows.

Now dive into the PHP executor, by installing XDebug.

Check xhprof – Facebook open sourced this about a year ago, it’s a PECL extension. The output is pretty cool, try it on your own site, Rasmus does show you how to use it. It shows you functions sorted by the most expensive to the least expensive.

For example, use $_SERVER[REQUEST_TIME] instead of time(). Use pconnect() if MySQL can handle the amount of webserver connections that will be persistent, etc.

After you have changed a lot of the stuff above, benchmark again with siege to see how much faster you are. In this case there is not much gained so far.

So keep going….the blogroll is very slow — Rasmus gets rid of it by commenting out in the sidebar.php file. I’d like to see something to make it “semi-dynamic” — that is, make it a static file that can be re-generated, since you might want the blogroll but links are not changed every second…..

At this point we’re out of low-hanging fruit.

HipHop is a PHP to C++ converter & compiler, including a threaded, event-driven server that replaces apache. Rasmus’ slide says “Wordpress is well-suited for HipHop because it doesn’t have a lot of dynamic runtime code. This is using the standard Wordpress-svn checkout with a few tweaks.”

Then, of course, benchmark again.

The first time you compile Wordpress with HipHop, you give it a list of files to add to the binary, it will complain about php code that generate file names, so you do have to fix that kind of stuff. There’s a huge mess of errors the first time you run it (”pages and pages”), and Rasmus had to patch HipHop (and Wordpress) but the changes in HipHop have been put back into HipHop, so you should be good for the most part.

Check out the errors, lots of them show logical errors like $foo.”bar” instead of $foo.=”bar” and $foo=”bar” instead of $foo==”bar” in an if statement. Which of course is nice for your own code, to find those logical errors.

(Wordpress takes in a $user_ID argument and immediately initializes a global $user_ID variable, which overwrites the argument passed in, so you can change the name of the argument passed in….)

You can also get rid of some code, things that check for existence of the same thing more than once. So it will take a bit of tweaking, but it’s worth it.

There are limitations to HipHop, for example:

• It doesn’t support any of the new PHP 5.3 language features
  
• Private properties don’t really exist under HipHop. They are treated as if they are protected instead.
  
• You can’t unset variables. unset will clear the variable, but it will still be in the symbol table.
  
• eval and create_function are limited
  
• Variable variables $$var are not supported
  
• Dynamic defines won’t work: define($name,$value)
  
• get_loaded_extensions(), get_extension_funcs(), phpinfo(), debug_backtrace() don’t work
  
• Conditional and dynamically created include filenames don’t work as you might expect
  
• Default unix-domain socket filename isn’t set for MySQL so connecting to localhost doesn’t work

and HipHop does not support all extensions — see the list Rasmus has of extensions HipHop supports.

Then Rasmus showed an example using Twit (which he wrote) including the benchmarks. He shows that you can see what’s going on, like 5 MySQL calls on the home page and what happens when you don’t have a favicon.ico (in yellow).

In summary, “performance is all about architecture”, “know your costs”.

Be careful, because some tools (like valgrind and xdebug) you don’t want to put it on production systems, you could capture production traffic and replay it on a dev/testing box, but “you just have to minimize the differences and do your best”.

PlanetMySQL Voting: Vote UP / Vote DOWN

Most of this stuff is not PHP specific, and Python or Ruby or Java or .NET developers can use the tools in this talk.

The session on joind.in, with user comments/feedback, is at http://joind.in/talk/view/1320.

Slides are at http://talks.php.net/show/confoo10

“My name is Rasmus, I’ve been around for a long time. I’ve been doing this web stuff since 1992/1993.”

“Generally performance is not a PHP problem.” Webservers not config’d, no expire headers on images, no favicon.

Tools: Firefox/Firebug extension called YSlow (developed by yahoo) gives you a grade on your site.

Google has developed the Firefox/Firebug pagespeed tool.

Today Rasmus will pick on wordpress. He checks out the code, then uses Siege to do a baseline benchmark — see the slide for the results.

Before you do anything else install an opcode cache like APC. Wordpress really likes this type of caching, see this slide for the results. Set the timezone, to make sure conversions aren’t being done all the time.

Make sure you are cpu-bound, NOT I/O bound. Otherwise, speed up the I/O.

Then strace your webserver processs. There are common config issues that you can spot in your strace code. grep for ENOENT which shows you “No such file or directory” errors.

AllowOverride None to turn off .htaccess for every directory, just read settings once from your config file….(unless you’re an ISP).

Make sure DirectoryIndex is set appropriately, watch your include_path. All this low-hanging fruit has examples on the common config issues slide.

Install pecl/inclued and generate a graph – here is the graph image (I have linked it because you really want to zoom in to the graph…)

In strace output check the open() calls. Conditional includes, function calls that include files, etc. need runtime context before knowing what to open. In the example, every request checks to see if we have the config file, once we have config’d we can get rid of that stuff. Get rid of all the conditionals and hard-code “include wp-config.php”. Examples are on the slide.

His tips to change:
Conditional config include in wp-load.php (as just mentioned)
Conditional did-header check in wp-blog-header.php
Don’t call require_wp_db() from wp-settings.php
Remove conditional require logic from wp_start_object_cache

Then check strace again, now all Rasmus sees is theming and translations, which he decided to keep, because that’s the good benefit of Wordpress – Performance is all about costs vs. flexibility. You don’t want to get rid of all of your flexibility, but you want to be fast.

Set error_reporting(-1) in wp-settings.php to catch all warnings — warnings slow you down, so get rid of all errors. PHP error handling is very slow, so getting rid of errors will make you faster.

The slide of warnings that wordpress throws.

Look at all C-level calls made, using callgrind, which sits under valgrind, a CPU emulator used for debugging. See the image of what callgrind shows.

Now dive into the PHP executor, by installing XDebug.

Check xhprof – Facebook open sourced this about a year ago, it’s a PECL extension. The output is pretty cool, try it on your own site, Rasmus does show you how to use it. It shows you functions sorted by the most expensive to the least expensive.

For example, use $_SERVER[REQUEST_TIME] instead of time(). Use pconnect() if MySQL can handle the amount of webserver connections that will be persistent, etc.

After you have changed a lot of the stuff above, benchmark again with siege to see how much faster you are. In this case there is not much gained so far.

So keep going….the blogroll is very slow — Rasmus gets rid of it by commenting out in the sidebar.php file. I’d like to see something to make it “semi-dynamic” — that is, make it a static file that can be re-generated, since you might want the blogroll but links are not changed every second…..

At this point we’re out of low-hanging fruit.

HipHop is a PHP to C++ converter & compiler, including a threaded, event-driven server that replaces apache. Rasmus’ slide says “Wordpress is well-suited for HipHop because it doesn’t have a lot of dynamic runtime code. This is using the standard Wordpress-svn checkout with a few tweaks.”

Then, of course, benchmark again.

The first time you compile Wordpress with HipHop, you give it a list of files to add to the binary, it will complain about php code that generate file names, so you do have to fix that kind of stuff. There’s a huge mess of errors the first time you run it (”pages and pages”), and Rasmus had to patch HipHop (and Wordpress) but the changes in HipHop have been put back into HipHop, so you should be good for the most part.

Check out the errors, lots of them show logical errors like $foo.”bar” instead of $foo.=”bar” and $foo=”bar” instead of $foo==”bar” in an if statement. Which of course is nice for your own code, to find those logical errors.

(Wordpress takes in a $user_ID argument and immediately initializes a global $user_ID variable, which overwrites the argument passed in, so you can change the name of the argument passed in….)

You can also get rid of some code, things that check for existence of the same thing more than once. So it will take a bit of tweaking, but it’s worth it.

There are limitations to HipHop, for example:

• It doesn’t support any of the new PHP 5.3 language features
  
• Private properties don’t really exist under HipHop. They are treated as if they are protected instead.
  
• You can’t unset variables. unset will clear the variable, but it will still be in the symbol table.
  
• eval and create_function are limited
  
• Variable variables $$var are not supported
  
• Dynamic defines won’t work: define($name,$value)
  
• get_loaded_extensions(), get_extension_funcs(), phpinfo(), debug_backtrace() don’t work
  
• Conditional and dynamically created include filenames don’t work as you might expect
  
• Default unix-domain socket filename isn’t set for MySQL so connecting to localhost doesn’t work

and HipHop does not support all extensions — see the list Rasmus has of extensions HipHop supports.

Then Rasmus showed an example using Twit (which he wrote) including the benchmarks. He shows that you can see what’s going on, like 5 MySQL calls on the home page and what happens when you don’t have a favicon.ico (in yellow).

In summary, “performance is all about architecture”, “know your costs”.

Be careful, because some tools (like valgrind and xdebug) you don’t want to put it on production systems, you could capture production traffic and replay it on a dev/testing box, but “you just have to minimize the differences and do your best”.

PlanetMySQL Voting: Vote UP / Vote DOWN