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Software Made Clear
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For engineers who want the mechanism, not the metaphor

Software, made clear.

One diagram per mechanism — databases, architecture, the CS foundations underneath both, and what it takes to run a change past a pipeline of agents.

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API handlervalidates, opens a transactionpage cachethe only fast layerB-tree indexthree hops to any keyheap file and write-ahead logwhere durability is decidedwriteread

THE ARGUMENT, IN SIX STEPS

STEP 1 / 6
A write arrives. It has been validated and a transaction is open — nothing is durable yet.
98PUBLISHED PAGES6LEARNING PATHS5LIVE VISUALISERS0PAYWALLS

What do you want to do?

Help me choose →

Start with the problem you recognise. You don’t need to know the technical term.

Understand software basics →

You can follow code, but the ideas underneath it still feel abstract.

Choose a system design →

You need to split responsibilities or explain a design decision to your team.

Understand a slow database →

A query is slow, an index seems ignored, or you want to understand how data is stored.

Build with coding agents →

You want AI to help ship changes, with checks and people in control.

Prepare for an interview →

You want to explain your reasoning, not memorise a list of answers.

Grow as an engineer →

You can ship code and want to understand what the next level asks of you.

Start where the writing is

See all 6 paths →

PERSISTENCE · 7 / 7 WRITTEN

How a database keeps your data

How a database actually keeps your data, in the order that makes each step explain the next. Seven steps from a row on a page to a deadlock in production.

Pages, heaps and tuplesWritten
The write-ahead logWritten
B-Tree vs LSM-TreeWritten
OLTP vs OLAPWritten
Why your index is not being usedWritten
Isolation levelsWritten
Deadlocks, seenWritten
Open the full map →

EXPLORE THE OTHER PATHS

ARCHITECTUREArchitecture in the real world 7 / 7 WRITTEN DISTRIBUTEDDistributed basics 2 / 6 WRITTEN FACTORYRunning a software factory 19 / 19 WRITTEN GROWTHGrowing as a developer 9 / 10 WRITTEN TREESTrees and traversal 3 / 5 WRITTEN
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NOT A SCREENSHOT — TRY IT

Insertion order decides the shape.

A drawing can only show one tree. Feed this one values and the shape follows the order you chose — with the height and the best possible height side by side as they come apart.

This tree is close to its best possible shape: a lookup costs at most 3 comparisons for 7 values.

All 5 visualisers →
NODES7
HEIGHT3
BEST POSSIBLE3

Latest

Everything on the site →
August 31, 2026 COMPARISON B-Tree vs LSM-Tree Take the B-tree when reads must stay predictable and the LSM-tree when writes outrun where you can place them — one bill now, one bill later, your choice. Read it →

A MECHANISM TO EXPLORE

B-TREEone shape, kept correct at all timesLSM-TREEmany sorted runs, merged later3 pages read, modified and written backmemtablewrite-ahead logthe write ends hereL0L1L21 append — the rest is paid by compaction, later
Explore B-Tree vs LSM-Tree →
August 31, 2026 DEEP DIVE Buffer overflows Learn why writing past the end of a buffer is rarely the real bug, what sits in the memory it lands in, and why the class still tops the weakness lists. Read it → August 31, 2026 DEEP DIVE Congestion control Learn why TCP carries two separate limits on how much it may send, which one the network controls, and why confusing them sends you tuning the wrong thing. Read it → August 31, 2026 DEEP DIVE Database replication See why a replica is fed the log rather than the data, what the default setting quietly trades away, and how much you actually lose when a primary dies. Read it → August 31, 2026 DEEP DIVE Dead letter queues See the four things that actually send a message to a dead letter queue, why only one of them is your code failing, and how the cycle protection works. Read it →

HOW THIS IS WRITTEN

Every claim here is traced to a primary source, and the page tells you which one.

Written by Sören Striewski · How this is written →

The picture carries the point

Every mechanism gets a diagram built to show that mechanism, and the prose only covers what the picture cannot. If a topic has no mechanism, it gets a table and a straight answer instead.

Traceable, not paraphrased

Nothing is written from other people's explainers. Each page names the documentation, specification or source it was checked against, and the date it was checked — so you can disagree with it at the source rather than take it on trust.

Free, and quiet

No paywall, no login, no cookie banner, no ads between you and the diagram. The newsletter is the only thing asked of you, and it is optional.

MAINTENANCE

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