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Mainframe Migration Tools: What Works and What Fails
3+ hour, 58+ min ago (1485+ words) This guide describes the categories of tooling that actually exist, what each one genuinely does well, and the specific places where each tends to fail on real workloads. It is written for the people who have to sign the business…...
SQLDungeon: Now with DuckDB
1+ hour, 40+ min ago (35+ words) SQL Dungeon grew a DuckDB marsh this weekend. Why, well because I wanted to learn it. SQL Dungeon started as a browser dungeon crawler where every room is a SQL puzzle …...
Window Functions in PySpark: A Practical Guide with ROW_NUMBER, RANK, LAG, LEAD, and Running Totals
5+ hour, 54+ min ago (104+ words) Non member readers can read it here for free If you work with Apache Spark, PySpark, Databricks, or SQL, sooner or later you will encounter a problem that looks deceptively simple: “For every customer, find their latest transaction.” “Calculate the…...
Ditch H2: PostgreSQL Repository Tests with Testcontainers and @ServiceConnection in Spring Boot 4
13+ hour, 8+ min ago (204+ words) Your repository tests are green. Then production throws a column “metadata” is of type jsonb but expression is of type character varying…Continue reading on Medium » Ditch H2: PostgreSQL Repository Tests with Testcontainers and @ServiceConnection in Spring Boot 4 Your repository tests…...
Recursive CTEs: How SQL Secretly Learned to Loop
19+ hour, 52+ min ago (454+ words) Ask a SQL query to find "all employees under this manager," and things get ugly fast if you don't know how many levels deep the org chart goes. A regular join handles one level. Two joins handle two levels. Nobody's…...
EXPLAIN Describes a Query. Production Is Everything Else That’s Running.
17+ hour, 47+ min ago (1398+ words) A while back I wrote about migrating a terabyte of banking data from Oracle to PostgreSQL with no downtime. The part people …...
The database connection pool was configured with 50 connections, so why did the 20th request time…
22+ hour, 36+ min ago (30+ words) The database connection pool was configured with 50 connections, so why did the 20th request time out? Understanding how parallel database queries inside a single HTTP request can exhaust your …...
Our users’ phones were the backup: rebuilding a lost database from app caches
23+ hour, 22+ min ago (223+ words) How expired cache entries on readers’ devices, server logs, and a year-old dump were merged back into MongoDB without …...
Vanilla PostgreSQL vs Amazon Aurora PostgreSQL
23+ hour, 58+ min ago (1187+ words) At the application level, Amazon Aurora PostgreSQL looks like PostgreSQL. You connect with PostgreSQL drivers, run SQL, use transactions, indexes, MVCC. Underneath, it is a different database architecture. One sentence explains most of the difference: Vanilla PostgreSQL couples the database engine…...
Pattern #007: Moving / Rolling Windows in SQL
1+ day, 20+ min ago (33+ words) How to calculate what happened over the last N days — without confusing it with a running total A product manager asks: “What was our average daily …...