101 articles · 35 databases · 63 topics
Practical tutorials, performance tuning and internals for SQL Server, PostgreSQL, MySQL, MongoDB, Redis and every engine in between — written by people who run them in production.
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PostgreSQLIntermediateRaising max_connections to 1000 usually makes things worse. Learn why Postgres connections are expensive, where they're leaking and how PgBouncer fixes it for good.
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SQLiteBeginnerWhat WAL mode changes compared with the default rollback journal, what it costs, when not to use it, and how to turn it on, check it and switch back.
#concurrency#configuration#transactions
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PostgreSQLBeginnerThe index exists, but the plan still shows a scan. Nine common reasons the optimizer can't (or shouldn't) use your index, and how to fix each one.
#execution-plans#indexing#performance
SQL ServerIntermediateSame proc, same code, suddenly 100× slower, and fast again when you run it in SSMS. Here's how parameter sniffing causes it, how to prove it and the fixes that actually hold.
#execution-plans#performance#troubleshooting
MySQLIntermediateError 1205 on a simple UPDATE, from code that doesn't even use transactions. Find the blocking session, spot the missing index that's locking too much and stop it coming back.
#locking#transactions#troubleshooting
SQLiteIntermediateWhy Python raises "database is locked", how timeout, isolation_level and autocommit interact, and the working pattern for threads, worker processes, SQLAlchemy, Django and aiosqlite.
#concurrency#locking#orm
SQL ServerBeginnerA 200 GB .ldf for a 20 GB database? Shrinking only treats the symptom. log_reuse_wait_desc tells you the real cause, and here's how to fix each one.
#maintenance#transactions#troubleshooting
SQLiteAdvancedHow the -wal and -shm files, read marks and checkpoints work, why a WAL grows without bound, and how to set checkpointing, journal_size_limit and synchronous.
#concurrency#configuration#internals
