PostgreSQL Is Using 90% of Your Disk. Here’s Where the Space Went.

WAL, dead tuples, indexes, tables, bloat, and the PostgreSQL queries I use to find the real culprit.

The alert arrives at 2:13 AM.

PostgreSQL disk usage: 90%

The application is still running.

Queries are still completing.

Nothing appears broken.

Yet there’s a problem.

At 90% utilization, there isn’t much room left for unexpected growth. A sudden spike in writes, a large deployment, a replication issue, or even a runaway transaction could push the database into a much more serious situation.

The obvious question becomes:

What’s consuming all the disk space?

You check the database size.

It’s large.

But that doesn’t tell you enough.

Is it:

• Tables?
• Indexes?
• TOAST data?
• Dead tuples?
• WAL?
• Replication slots?
• Temporary files?
• A table that’s been quietly growing for months?

This is where PostgreSQL’s storage functions and system views become incredibly useful.

Because when a database reaches 90% disk utilization, guessing is dangerous.