MySQL vs PostgreSQL: The Battle for Your Data Integrity

Most developers treat their database choice like a default setting. You spin up a new CentOS 6 instance, run yum install mysql-server, and call it a day. But if you are building a system that needs to scale beyond a simple WordPress blog, blindly choosing the default stack is a recipe for 3 AM pages and corrupted tables.

As a Systems Architect managing infrastructure across the Nordics, I've seen the aftermath of poor database decisions. I've watched e-commerce sites crash during holiday rushes because of MyISAM table locking, and I've seen financial apps lose data because of silent type coercion. With the recent maturity of MySQL 5.5 and the advanced features of PostgreSQL 9.1, the landscape in 2012 is more competitive than ever. The question isn't just "which is faster?"—it's "which one will survive your workload?"

The Case for MySQL 5.5: Speed and Ubiquity

MySQL is the engine of the web. It is everywhere. With the release of version 5.5, Oracle finally made InnoDB the default storage engine. This is a massive shift from the dark days of MyISAM. We finally have reliable ACID compliance and row-level locking out of the box. For read-heavy workloads—think content management systems, forums, or simple logging—MySQL is often faster and easier to replicate.

However, performance requires tuning. The default my.cnf on most distributions is laughably small, optimized for servers with 512MB of RAM. If you are running on a CoolVDS instance with dedicated RAM, you are wasting resources.

Here is a baseline configuration for a 4GB RAM node running MySQL 5.5 exclusively:

[mysqld]
# storage engine
default-storage-engine = InnoDB

# critical for performance - set to 70-80% of available RAM
innodb_buffer_pool_size = 3G

# prevent double buffering by OS
innodb_flush_method = O_DIRECT

# strictly adhere to ACID compliance (set to 0 or 2 for speed at risk of data loss)
innodb_flush_log_at_trx_commit = 1

# separate file for each table
innodb_file_per_table = 1

The innodb_buffer_pool_size is the single most important knob you can turn. It determines how much data and how many indexes MySQL caches in memory. If your dataset exceeds this pool, you hit the disk. And if you are hitting spinning rust instead of SSDs, your latency spikes from microseconds to milliseconds.

The Case for PostgreSQL 9.1: Data Integrity and Complexity

If MySQL is a drag racer, PostgreSQL is a tank. It is built for correctness. While MySQL 5.5 is getting better at strictness, PostgreSQL has been strict for decades. Version 9.1 introduced synchronous replication, which is a game-changer for high-availability setups in the enterprise.

PostgreSQL excels at complex queries. Its query planner is significantly smarter than MySQL's. It supports Hash Joins and Merge Joins, whereas MySQL is often limited to Nested Loop joins. Furthermore, with the hstore extension, we are seeing the beginning of NoSQL capabilities right inside a relational engine.

However, Postgres manages memory differently. It relies heavily on the operating system's filesystem cache. Here is how you tune postgresql.conf for that same 4GB server:

# memory configuration
shared_buffers = 1GB  # typically 25% of RAM
effective_cache_size = 3GB # estimated OS cache available

# checkpoint handling
checkpoint_segments = 32
checkpoint_completion_target = 0.9

# query tuning
work_mem = 16MB # per operation memory
maintenance_work_mem = 256MB

Pro Tip: Be careful with work_mem. This limit is applied per sort or hash operation. If you have 100 connections running complex queries with 3 sorts each, you can exhaust your RAM and force the OOM killer to murder your database process.

I/O Latency: The Silent Killer

You can tune buffers all day, but databases are ultimately bound by Input/Output operations per second (IOPS). This is where your choice of hosting provider becomes an architectural decision, not just a billing one.

In a standard shared hosting environment, or even on budget VPS providers using OpenVZ, you are fighting for disk I/O with hundreds of other tenants. If a "noisy neighbor" decides to run a massive backup or compile a kernel, your database queries will stall. This is called "I/O Wait," and it destroys application performance.

We see this constantly with clients migrating to us. They complain that MySQL is "slow," but top shows CPU usage at 5%. The real culprit is %wa (iowait). You can diagnose this with iostat:

root@db01:~# iostat -x 1
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           4.50    0.00    2.10   45.20    0.00   48.20

Device:         rrqm/s   wrqm/s     r/s     w/s   svctm   %util
sda               0.00    12.00   85.00   45.00    8.50   98.50

If %iowait is high (like the 45% above) and %util is near 100%, your disk cannot keep up. This is why CoolVDS utilizes KVM virtualization with strict resource isolation and high-performance enterprise SSD storage. Unlike OpenVZ, KVM ensures that your allocated resources are actually yours. For databases, the low latency of SSDs compared to traditional 15k RPM SAS drives is not just a luxury; it is becoming a requirement for modern web applications.

Legal Compliance and Location: The Norwegian Context

Beyond technical specs, we must address the legal reality of operating in Europe. Under the Norwegian Personal Data Act (Personopplysningsloven) and the EU Data Protection Directive, you are responsible for where your user data lives. Storing sensitive customer data on budget servers in the US might save you a few kroner, but it exposes you to legal risks regarding data jurisdiction.

Hosting within Norway offers two distinct advantages:

1. Compliance: Your data remains under Norwegian jurisdiction, satisfying the requirements of Datatilsynet (The Data Protection Authority).
2. Latency: The speed of light is a hard limit. If your users are in Oslo, serving data from Frankfurt or Amsterdam adds 20-30ms of round-trip time. Hosting locally at the NIX (Norwegian Internet Exchange) reduces this to near-zero, making your database feels instantaneous to the application server.

Comparison Summary

Conclusion

If you are migrating a legacy application or building a read-heavy web service, MySQL 5.5 on a tuned InnoDB engine is a solid, pragmatic choice. It is familiar and fast. However, if you are designing a system requiring complex transactions, strict data integrity, or geospatial features, PostgreSQL 9.1 is the superior architect's choice.

Regardless of the engine, the underlying metal matters. Don't let IOPS bottlenecks strangle your database performance. Test your schema on a platform built for low latency and stability.

Ready to benchmark your database? Deploy a KVM instance on CoolVDS today and experience the difference of local Norwegian hosting.