Investigate a performance problem
A fixed-scope diagnostic of one slow, locking or expensive workload: written findings, prioritised next steps and a handover to your engineers.
Independent MySQL, MariaDB & Aurora MySQL consulting
Understand your database bottleneck. Leave with a clear plan.
I investigate slow queries, locks that keep coming back and latency nobody can explain, for software teams and agencies. You work with me directly, and your engineers get findings and a plan they can work through in order.
The scope and the fee are fixed before I start, and you don't need a support contract.
Planning a new setup instead? See architecture design, review and build for MySQL, MariaDB and Aurora MySQL.
Illustrative sample
Sample report: slow order history in a multi-tenant application
Why does the order-history page become slow for some tenants, and what should the team test first?
- No index matches the filter and sort together
- Deep pages use OFFSET
Estimate the large-tenant plan with EXPLAIN FORMAT=JSON before any EXPLAIN ANALYZE.
Synthetic MySQL scenario; no customer data or measured results.
Read the MySQL sample →Two ways to start
Investigate a problem, or design the system
Design, review or build a database architecture
Topology, failover and growth, planned with your team before the choices are hard to undo. You get a written design, and a separately scoped build if you want one.
From real audits
Anonymised write-ups of customer engagements, with the evidence each one used.
- Why a Galera cluster was slower than staging for an online shopA Galera cluster where one cookie-consent lookup took 13% of the query time and examined about 962,000 rows to return one.
- A MySQL server that spent half its time waiting for locksA MySQL server that spent 49% of its query time waiting for row locks held by two statements.
- A Galera cluster that became unstable when it was stretched to a second data centreA seven-node Galera cluster that accepted no writes anywhere for about 16 seconds when the link between its two data centres dropped.
- A CPU-saturated MySQL server: full scans, long procedures and idle transactionsOne procedure call ran for 7,179 seconds and returned no rows.
Who does the work
You work with me, not with a team behind me.
I'm Krzysztof Książek, and DB-Ex is my independent consultancy. I scope the work, do the investigation, write the findings and hand them over myself.
Production database experience
Database reliability engineer on a large Amazon Aurora fleet since April 2025, including major version upgrades and schema and query work with development teams. Earlier, MySQL operations and performance reviews as an operational DBA (2012–2015).
Career summary →Technical work you can inspect
These articles show how I work through a problem: what the evidence says, what it doesn't, and what I'd test next.
The lab code and recorded runs are public: database-labs on GitHub.
- MySQL backup lab, part 9 – the harness that records evidenceHow a lab records its own evidence and stops on failure instead of reporting a green result.
- ClickHouse HA on a Mac, part 3: insert_quorum, the no-loss proof, and taking it to productionA no-loss check repeated over three runs, and what I'd change before production.
Support leadership and technical communication
Head of Support at Severalnines (2019–2025) after four years as a senior support engineer: complex customer escalations on MySQL and MariaDB, technical guides and webinars, and a Percona Live Europe talk on MySQL load balancers.
Where a focused investigation helps
Three common starting points
Queries are slow and nobody's sure why?
I find out what the evidence actually supports before you change anything.
Planning an upgrade or a failover change?
I go through the plan, point out what's assumed but untested, and write down how to test it.
A client's MySQL problem is more than your team has time for?
I do the investigation and write it up. You keep the client and the delivery.
The main offer
Performance diagnostic (MySQL, MariaDB, Aurora MySQL)
I take one slow, locking or expensive workload, find out what the evidence supports and write it up for your engineers, most important step first.
What you receive
- Findings with their supporting evidence
- Prioritised recommendations
- A plan for validating changes
- Technical handover to your team
One environment and one main question. Scope and schedule are agreed before I start. Fixed fee, agreed after a free scope review call.
The scope review is a free call. We pin down the one question you need answered and what you need from it, and I follow up with a written proposal.
The effort limit is the scope of work we agree up front. It doesn't grow unless we both agree to extend it.
How it runs
- Scope
- Evidence review
- Findings and recommendations
- Handover
For agencies and consultancies
Specialist database help for your client projects
If a client's MySQL problem needs more digging than your team has time for, bring me in. You don't have to hire anyone.
You retain the client relationship and implementation work. I provide the database investigation, written findings, and handover to your technical team.
Selected proof and technical writing
See how I approach database problems
- RecoveryLab
MySQL – test your backup by restoring it as a replica
A successful backup job does not prove you can recover. This lab restores a backup as a replica and records the evidence for each scenario.
- ArchitectureLab
MySQL async replication HA, part 2 – the source dies
I killed the MySQL source under load: two seconds at zero throughput, one error per connection, and two failover-hook bugs found on the way.
- Performance Illustrative
Sample MySQL diagnostic: slow order history in a multi-tenant application
The full structure of a diagnostic report: evidence with its provenance, findings separated from hypotheses, missing evidence, and validation steps.
Have a database question worth investigating?
Tell me what you run, what's going wrong and what you need to know. I'll tell you whether I can help with a fixed-scope piece of work, and if I can't, I'll say so.