The callback that quietly doubled our database
A Rails after_save callback silently duplicated database rows: how the symptom appeared, why the obvious suspect was innocent, and the real root cause.
Tag: database
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.
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.
Zero-downtime GKE upgrades with PostgreSQL failover
Blue/green node pools plus a Kubegres replica promotion let you upgrade a GKE cluster, PostgreSQL included, without a maintenance window.
Transactions, touch, and async rollups for derived data in Rails
Keeping counters and summaries accurate in Rails without slowing down writes means separating core data in a transaction from derived data updated after commit.
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.
load_async in Rails 8: loading associations concurrently
Rails 8's load_async runs association queries concurrently instead of one after another, and getting it right means sizing your connection pool correctly.
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.
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.
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.
Avoiding Duplicate Record Errors in Rails Under Concurrency
Two concurrent requests can both pass an exists? check and race to insert the same row; here is why, and how to write idempotent Rails controllers.
Handling Out-of-Order Updates in Async Rails Workflows
When async updates to the same record can finish in any order, the oldest write can silently overwrite the newest one; here is how to stop that.
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.
API Design for Time Slot Replacement in Booking Systems
How to design a booking API that replaces regular time slots with alternatives, using server-side merging, cache versioning, and idempotency keys.
Kubernetes Node Upgrades: Cordon, Drain, and Failover
A cordon-drain-upgrade runbook for Kubernetes nodes, plus the PodDisruptionBudgets, priority classes, and lifecycle hooks that prevent outages.
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.
N+1 Queries in Rails: What Silently Breaks `includes`
How ActiveRecord's includes prevents N+1 queries in Rails, and the common mistakes with order, filtering, and pluck that silently break it.
Laravel Model: `save()` vs. `saveOrFail()`
When Laravel's save() silently returns false versus when saveOrFail() throws, and how to pair both with validation and database transactions.
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.
Speeding Up Nested JSON Serialization in Rails
Caching, the Oj gem, eager loading, background jobs, and load_async each cut serialization time for deeply nested Rails associations like classrooms and scores.
delete_all vs destroy_all in Rails: Callbacks and Associations
delete_all skips callbacks and dependent associations while destroy_all runs them, and picking the wrong one silently breaks counter caches and cascades.
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.
Rails N+1 Queries: joins vs preload vs eager_load vs includes
What joins, preload, eager_load, and includes actually do in ActiveRecord, shown with real SQL logs, plus the chained calls that quietly bring the N+1 back.
Fragment Caching a Large List That Changes Constantly
How splitting static and dynamic fields, granular fragment caching, and incremental loading keep a large, frequently updated list fast without stale data.
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.
Shared Databases Between Microservices Are a Code Smell
When two services share one database, a schema change in either one can silently break the other, and here is how to split ownership with APIs or events.
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.
Rails unscope: removing default scope conditions
How ActiveRecord's unscope method selectively removes where and order conditions from default scopes, with examples and alternatives like merge and unscoped.
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.