Zombie PostgreSQL replicas: the WAL segment removed deadlock
PostgreSQL replicas on Kubernetes can get stuck in a WAL segment removed loop that passes liveness checks, and three fixes stop it for good.
Category: database
Why pg_dump backups on a PostgreSQL replica fail intermittently
Running pg_dump on a PostgreSQL replica can fail with conflict with recovery errors because the backup is a long read transaction colliding with WAL replay.
Postgres conflict with recovery: why replicas cancel queries
A PostgreSQL replica cancels long queries with conflict with recovery errors during VACUUM replication, and hot_standby_feedback fixes it without downtime.
Redis High Availability: Shared Sessions and Fault Tolerance
How to split Redis into isolated session, cache, and Sidekiq instances so a cache blip never logs users out or stops background jobs.
Polymorphic Indexes in MySQL: Type-First or ID-First?
A practical comparison of [type, id] versus [id, type] composite index order for polymorphic associations in Rails and MySQL, and how to choose.
Redis Cleanup and Memory Management in Kubernetes
A production-tested guide to keeping Redis healthy in Kubernetes: memory control, safe cleanup patterns, Sidekiq pitfalls, backups, and troubleshooting.
Fixing the Asia/Rangoon Postgres Error on Alpine Linux
If you recently updated your Docker images and were greeted by a PG::InvalidParameterValue: ERROR: time zone "Asia/Rangoon" not recognized, you aren't alone.
PostgreSQL on Ubuntu: install, user setup, and auth debugging
Install PostgreSQL from the PGDG repo on Ubuntu, set up a matching development role, and debug the password authentication failures Rails hits most.
PostgreSQL MD5 to SCRAM-SHA-256: a zero-downtime migration
PostgreSQL 18 deprecates MD5 authentication, and migrating to SCRAM-SHA-256 in mixed mode lets you switch pg_hba.conf without downtime or forced app changes.
localhost vs 127.0.0.1 vs 0.0.0.0: Network Binding Explained
Why localhost, 127.0.0.1, 0.0.0.0, and * behave differently for MySQL clients and services, and how to find and fix a local port conflict between Docker and SSH.
PostgreSQL 18: What's New and How to Upgrade
PostgreSQL 18 adds better query parallelism, parallel logical replication apply, and more flexible partitioning, plus the pg_upgrade and dump/restore paths to get there.
Designing a Schema for an Optional Attribute
A one-line feature request, recording why a student failed a course, walks through three schema options: a nullable column, a normalized table, and jsonb.
Troubleshooting pgpool Connection Termination in Kubernetes
Intermittent pgpool connection drops in Kubernetes usually trace to max_connections, idle timeouts, or NetworkPolicy issues, found layer by layer.
Managing Temporary Data in Multi-Step Rails Forms
Multi-step Rails forms need somewhere to hold data between steps, and this compares session storage, direct Redis caching, and temporary DB rows for that job.
PostgreSQL JSONB vs Linking Tables for Relationships
Comparing PostgreSQL jsonb columns against a traditional linking table for modeling course prerequisites, and where a hybrid of both makes more sense.
MySQL vs PostgreSQL: Foreign Key Deadlock Contention
How foreign key checks cause deadlock contention in MySQL InnoDB versus PostgreSQL, and why PostgreSQL's FOR KEY SHARE lock reduces the risk considerably.
Idempotent Rails Requests with a Redis Semaphore Lock
How to stop duplicate Rails requests from creating the same record twice, using a Redis-backed semaphore lock instead of chasing a race condition.
Redis Sentinel Split-Brain: Fixing It on Kubernetes
How Redis Sentinel split-brain happens during Kubernetes node maintenance, and the sentinel tuning, anti-affinity, and PDB changes that stopped it.
Deadlocks in MySQL and PostgreSQL: Foreign Keys vs Performance
How deadlocks form in MySQL and PostgreSQL under concurrent updates, and the trade-off between foreign key integrity and write throughput.
Catching Database Configuration Drift Between Microservices
Two services sharing a database can pass every test and still fail in production if their DB configuration silently drifts apart.
Ordering by an Associated Column Without Breaking includes
Why ordering ActiveRecord results by an associated table's column breaks with includes, and how references, Arel, and left_joins fix it for good.
Common MySQL Commands: Databases, Users, and Grants
A quick-reference list of MySQL and MariaDB commands for databases, tables, users, and grants, kept for copy-pasting from the shell.
Materialized Views: Speeding Up Queries with a Tradeoff
Materialized views cache expensive PostgreSQL queries as physical tables, trading storage and refresh cost for fast reads, plus how pgpool fits in.
PostgreSQL Sequence Conflicts After an Upgrade: How to Fix Them
Upgrading PostgreSQL can leave sequences out of sync with table max values, causing duplicate-key errors and blocked sign-ins, fixed here with SQL and bash.
Zero-Downtime PostgreSQL Upgrades With Logical Replication
A bash script that sets up PostgreSQL logical replication, publications, and subscriptions to perform a major-version upgrade without downtime.
Redis Sentinel: How Automatic Failover Actually Works
How Redis Sentinel provides high availability: quorum-based monitoring, master election, automatic failover, and what your client applications must do to follow along.
Postgres 'Too Many Connections': Debugging Pgpool-II Limits
Debugging a Postgres 'too many connections' error through Pgpool-II's num_init_children and max_pool settings, and the fix that stopped clients queueing.
Scaling PostgreSQL on Kubernetes with Kubegres
How Kubegres brings primary/standby failover, automatic backups, and PITR to a self-hosted PostgreSQL cluster on Kubernetes without a managed database bill.
Pgpool-II: Middleware for PostgreSQL
Pgpool-II sits between PostgreSQL and its clients as a connection pooler and load balancer, and this covers the Kubernetes setup that keeps writes consistent.
Soft Delete in Rails: Discard vs ActsAsParanoid
A comparison of Discard and ActsAsParanoid, the two common Rails soft-delete gems, and the query and unscope pitfalls each one introduces.
Database Auditing: pg_audit vs audited vs paper_trail
A comparison of database auditing options, pg_audit, audited, paper_trail, Hibernate Envers, and SQL Server temporal tables, and when each one fits.