SQLite
WAL Mode: One Writer, Many Readers
SQLite's default journal blocks readers during a write. WAL mode does not, and that single difference decides whether SQLite suits a concurrent service.
· 2 min
Databases · Queries · Operations
Databases, queries and the people who run them.
In-depth articles on PostgreSQL, MySQL, SQL Server, Oracle and modern data engineering — written for developers, analysts and database administrators.
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NoSQL
Document or Relational: Read-Time or Write-Time Cost
Relational modeling describes the entities and lets queries follow. Document modeling inverts that, and the inversion is the whole trade.
· 4 min
PostgreSQL
Connection Pool Sizing: Why More Connections Make It Slower
Past the point where the server can execute work in parallel, adding connections adds queueing rather than throughput — and moves the queue somewhere worse.
· 4 min
SQL Fundamentals
Composite Indexes: One Ordering, Not Three
Column order decides which queries a composite index can serve. The rule follows from the structure, and so do the cases where it does not hold.
· 3 min
MySQL
Why the Primary Key Is in Every Secondary Index
InnoDB stores the table inside its primary key. Almost every MySQL indexing consequence, good and bad, follows from that single decision.
· 3 min
PostgreSQL
Transaction Pooling Breaks Only Under Load
Transaction pooling is what makes PgBouncer worth deploying, and it silently removes session state your application may depend on.
· 3 min
Featured · sql-fundamentals
N+1 Queries: What the ORM Is Actually Doing
One query for the list, then one more for every item in it. The cost is per statement, which is why the profiler shows a fast database and a slow request.
2026-08-30 · 3 min
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One article to begin with
series
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- 1 partIndexing From First PrinciplesThree parts on index design driven by structure rather than rules of thumb — column order, what covering an index really costs, and the case where an index is valuable because of what it leaves out.
- 1 partReading Execution PlansThree parts on turning a plan from a wall of text into a diagnosis — which EXPLAIN variant answers which question, the order to read a plan tree in, and the one comparison that localizes most problems.