Category Archives: CTO/CIO

Migration to MySQL – What is it and why is it important?

MySQL is a relational database that backs many internet websites and enterprise applications.  Like all enterprise software, it has a whole complement of features which are well documented, such as data types, storage engines, transactional behaviors and so forth.  It also has a set of processes, many of which involve how software operates on Linux servers, such as how it gets installed, where binaries and libraries will get placed, where to find logfiles, and how to move directories and set permissions.  Thirdly it is important to understand the culture, in this case Unix-based, forum discussions and community contributions as an open-source project.

MySQL can do much of the workhorse kind of stuff you see in databases like Oracle or SQL Server, but sometimes it achieves those goals in very different ways.  For instance there are many open-source projects that support and surround the database, such as mysqltuner an analysis script, innotop a unix top-like utility for monitoring on-going activity in the database, and maatkit a whole suite of tools that build on and expand the features already present in the MySQL database.

Some Limitations in MySQL

  1. Complex queries and subqueries specifically can be problematic in MySQL.  If you’re used to writing huge queries in Oracle, and having the CBO figure everything out for you, you’ll be in for a surprise with MySQL.  Keep your queries simple, proper columns indexed and avoid complex joins where possible.  The EXPLAIN facility is available to you and at your disposal.  Use it!
  2. Vertical Scalability problems – primarily addressed in 5.5, the latest version of MySQL, previously the database did not scale well on greater than four processor boxes.  SMP or Symmetric Multiprocessing servers were less common 10-15 years ago when MySQL was in it’s infancy, and development is slowly catching up with the big iron of today.
  3. There is no flashback table, tablespace or database that you might find in other databases such as Oracle.  You can achieve the same thing with point-in-time recovery, so keep regular backups of your database, and also backup the transaction logs.
  4. MySQL can do JOINs, but only with the nested loops algorithm.  It can’t do sort merge join or hash join.
  5. MyISAM is the default table type and storage engine.  It is not crash safe and not transactional.  On new installations it’s recommended that you change this to InnoDB and use InnoDB for most if not all of your tables.  It’s very reliable and very fast!
  6. There is a query cache, but it caches result sets not query plans!  It also has some performance issues and shows some erratic behavior on larger SMP boxes.  Query plans are cached on a session basis, but when a session is closed and reopened, MySQL must reparse and reexecute that query.
  7. MySQL does not have a facility like Oracle’s Real Application Clusters.  It does have NDB Cluster which is an all-in-memory clustering solution.  Despite it’s promise, it tends to have very serious performance problems with any type of join, and is mainly good for single table index-based lookups.  If managed well it can increase availability but will probably reduce performance.
  8. MySQL’s default replication solution is statement based.  Although it is easy to setup, it breaks almost as easily, sometimes with resolvable errors, and sometimes silently.  Consider row-based replication, and definitely make use of Maatkit’s mk-table-checksum and mk-table-sync tools.  Also be sure to do thorough and regular monitoring of your replication setup.
  9. There are no in-built materialized views or snapshots in MySQL.  There is an open-source project called Flexviews by Justin Swanhart that provides this facility to the MySQL community.
  10. MySQL provides stored procedures, triggers and functions as a regular feature to the database.  However I would use them with caution.  They are very difficult to edit, troubleshoot and diagnose when they are causing troubles.  Also as with the query plan caching, stored procedures are cached at the session level, so they can be expensive to execute over and over again in different areas of your application.  They can cause real performance problems.
  11. There is no in-built mechanism for auditing that you find in relational databases such as Oracle 11g.
  12. Only b-tree indexes are supported, no bitmap indexes, index-organized tables, clustered indexes or other more exotic index types.
  13. ALTER TABLE is generally a locking and blocking operation.  For example if you add a new column or change a columns data type, the entire table will be locked for the duration of the operation.  This will be a surprise coming from the Oracle world where these type of operations can routinely be done online.

MySQL’s Strengths Are Numerous

  1. Install with an RPM using Yum or Aptget.  Fast & simple!
  2. Works great in the cloud, using MySQL Community distro, Percona distro, or Amazon’s own RDS solution.
  3. Comes out-of-the-box with an excellent command line shell providing all sorts of features and power that are constant frustrations on the Oracle side.  Command history, standard input/output redirection support, a full compliment of features and options, and easy autologin with a user level my.cnf file which fits in nicely with the global settings as well.
  4. A simpler mechanism to serve unique id columns with the auto-increment data type.  Although Oracle’s sequence method is extremely scalable, for many many developers it is troublesome and confusing.
  5. Good support of the LIMIT clause allowing an easier method for developers to fetch a subset of data.
  6. A huge community of users, forums, and support in third party applications such as monitoring (Nagios etc…) as well as metrics collection (Munin, Cacti, OpenNMS, Ganglia etc.)
  7. Great visibility of system variables with SHOW VARIABLES.  Many can be changed dynamically as well, just like Oracle.
  8. Great visibility of internal system state with SHOW PROCESSLIST.
  9. System counters for all sorts of internal instrumentation data using SHOW STATUS and SHOW INNODB STATUS.  Ultimately it is not as comprehensive as Oracle’s own data dictionary and millions of instrumentation counts.  However Oracle could take a huge page out of the MySQL book in terms of usability.  The obfuscation of Oracle’s internal kernel state makes it all but unusable by most.
  10. innotop, the utility much like the unix TOP facility that all Unix & Linux folks love, it provides instant visibility into what queries are running, what work is being done, and what is blocking.  Oracle could really take a page from this playbook, as this tool is so invaluable.
  11. The incredible Maatkit, a veritable goldmine of great community contributed powertools.  Query analyzers, profilers, log tools, replication tools, data archiver, a find facility, and a whole lot more!

Sean Hull discusses further on Quora – What considerations are important when migrating to MySQL?

Scalability – What is it and why is it important?

Scaling comes in a few different flavors.  Vertical scaling involves growing the computing power of a single server, adding memory, faster or more CPUs and/or faster disk I/O.

Horizontal scaling involves adding additional computing resources or servers in parallel and then load balacing across them.

Scalability refers to applications which facilitate scaling well.  With web applications, the middle tier aka the webservers are fairly easy to scale horizontally and most enterprise class applications already do this with commercial load balancers – with either hardware or software.

Doing the same with the database tier, however can be trickier.  Enter MySQL replication to facilitate a fairly painless horizontal scalability.  Build your application architecture with read-only transactions, and write/update transactions segmented apart, and you can send the latter to one master database, and the former to a handful of replicated slaves.  With a typical web application that is less than 10% writes, and 90% reads, there is the potential to add as many as 5-10 servers horizontally to increase application throughput by as much as 500-1000%.

Sean Hull asks on Quora: What is scalability and why is it important?

Amazon EC2 Outage – Failures, Lessons and Cloud Deployments

Now that we’ve had a chance to take a deep breath after last week’s AWS outage, I’ll offer some comments of my own.  Hopefully just enough time has passed to begin to have a broader view, and put events in perspective.
Despite what some reports may have announced, Amazon wasn’t down, but rather a small part of Amazon Web Services went down.  A failure, yes.  Beyond their service level agreement of 99.95% yes also.  Survivable, yes to this last question too.

Learning From Failure

The business management conversation du jour is all about learning from failure, rather than trying to avoid it.  Harvard Business Review’s April issue headlined with “The Failure Issue – How to Understand It, Learn From It, and Recover From It”.  The economist’s April 16th issue had some similarly interesting pieces one by Schumpeter “Fail often, fail well”,
and another in April 23rd issue “Lessons from Deepwater Horizon and Fukushima”.
With all this talk of failure there is surely one takeaway.  Complex systems will fail and it is in the anticipation of that failure that we gain the most.  Let’s stop howling and look at how to handle these situations intelligently.

How Do You Rebuild A Website?

In the cloud you will likely need two things.  (a) scripts to rebuild all the components in your architecture, spinup servers, fetch source code, fetch software and configuration files, configure load balancers and mount your database and more importantly (b) a database backup from which you can rebuild your current dataset.

Want to stick with EC2, build out your infrastructure in an alternate availability zone or region and you’re back up and running in hours.  Or better yet have an alternate cloud provider on hand to handle these rare outages.  The choice is yours.

Mitigate risk?  Yes indeed failure is more common in the cloud, but recovery is also easier.  Failure should pressure the adoption of best practices and force discipline in deployments, not make you more of a gunslinger!

Want to see an extreme example of how this can play in your favor?  Read Jeff Atwood’s discussion of so-called Chaos Monkey, a component whose sole job it is to randomly kill off servers in the Netflix environment at random.  Now that type of gunslinging will surely keep everyone on their toes!  Here’s a Wired article that discusses Chaos Monkey.

George Reese of enStratus discusses the recent failure at length.  The I would argue calling Amazon’s outage the Cloud’s Shing Moment, all of his points are wisened and this is the direction we should all be moving.

Going The Way of Commodity Hardware

Though it is still not obvious to everyone, I’ll spell it out loud and clear.  Like it or not, the cloud is coming.  Look at these numbers.

Furthermore the recent outage also highlights how much and how many internet sites rely on cloud computing, and Amazon EC2.
Way back in 2001 I authored a book on O’Reilly called “Oracle and Open Source”.  In it I discussed the technologies I was seeing in the real world.  Oracle on the backend and Linux, Apache, and PHP, Perl or some other language on the frontend.  These were the technologies that startups were using.  They were fast, cheap and with the right smarts reliable too.

Around that time Oracle started smelling the coffee and ported it’s enterprise database to Linux.  The equation for them was simple.  Customers that were previously paying tons of money to their good friend and confidant Sun for hardware, could now spend 1/10th as much on hardware and shift a lot of that left over cash to – you guessed it Oracle!  The hardware wasn’t as good, but who cares because you can get a lot more of it.

Despite a long entrenched and trusted brand like Sun being better and more reliable, guess what?  Folks still switched to commodity hardware.  Now this is so obvious, no one questions it.  But the same trend is happening with cloud computing.

Performance is variable, disk I/O can be iffy, and what’s more the recent outage illustrates front and center, the servers and network can crash at any moment.  Who in their right mind would want to move to this platform?

If that’s the question you’re stuck on, you’re still stuck on the old model.  You have not truely comprehended the power to build infrastructure with code, to provision through automation, and really embrace managing those components as software.  As the internet itself has the ability to route around political strife, and network outages, so too does cloud computing bring that power to mom & pop web shops.

Conclusions

  • Have existing investments in hardware?  Slow and cautious adoption makes most sense for you.
  • Have seasonal traffic variations?  An application like this is uniquely suited to the cloud.  In fact some of the gaming applications which can autoscale to 10x or 100x servers under load, are newly solveable with the advent of cloud computing.
  • Are you currently paying a lot for disaster recovery systems that primarily lay idle.  Script your infrastructure for rebuilding from bare metal, and save that part of the budget for more useful projects.