ActiveRecord threads can open one database connection per thread, quickly exhausting server limits. Rails reuses and releases connections automatically, but manual cleanup is sometimes needed.

Rails data can be passed to Unpoly compilers through data-* for simple strings and up-data for objects, arrays, and nested values.

Common Unpoly compiler selector strategies for reusable components, one-off view behavior, configurable attributes, and universal element enhancements.

Keeping project estimates aligned with the remaining budget prevents overruns when requirements change and project management overhead shifts.

Passing last_modified without an object skips ETag generation, so second-level timestamps can make distinct responses look identical and break cache-related tests.

Events from controls inside a disabled fieldset stop bubbling in Firefox, unlike Chrome and IE/Edge, which can break document-level listeners and delegated handlers.

Large-table COUNT(*) queries can be slow when only a threshold like 100+ matters; a LIMITed subquery stops early and avoids scanning every row.

RSpec truncates long inspected values to 200 characters, which can hide the real cause of failing specs. Raising max_formatted_output_length reveals more of the error message.

Ruby 1.9+ \w and \d stay ASCII-only; Unicode-aware POSIX character classes match letters, digits, and other script-specific characters.

Pause expensive periodic work when a tab is hidden to save battery and mobile data; document.hidden and visibilitychange let background pages go passive.

Static analysis for GitHub Actions workflow security and hardening finds unsafe interpolation, weak defaults, and unpinned actions; some warnings can be auto-fixed.

rails db:migrate on fresh databases now loads db/schema.rb or db/structure.sql first, which can skip data-manipulation migrations and leave state incomplete.

Icons and other inline blocks can be centered against capital letters instead of the text baseline. vertical-align with font metrics or 1lh gives a reliable result.

Temporary files in Ruby are removed automatically when no reference remains, and early unlink prevents stale paths and unauthorized access.

Concurrent requests can overwrite each other in Rails; pessimistic locking makes one transaction wait so only one update wins when a record is loaded or saved.

Sites with unusual HTTPS setups help verify browser certificate handling, proxy interference, and security-product side effects.

ActiveType 1.2 allows modifying has_many and similar associations after definition, useful for form models that need custom record types.

Sass compilation can be a build bottleneck. sass-embedded is a drop-in replacement for the deprecated sass package and is often about 50% faster.

Run a Docker container with a different perceived system time by injecting faketime via LD_PRELOAD and a mounted library path.

ActiveJob and GoodJob can swallow exceptions, causing silent background job failures. Subscribing to job events and on_thread_error restores exception notifications and adds failure context.

Opinionated formatting for JavaScript and TypeScript can remove whitespace debates and keep code consistent, with a small config and automatic reformatting.

User input often breaks integer conversion with exceptions or misleading zeros. Integer(..., exception: false) and ActiveModel type casting return nil instead.

Rails log files rotate automatically around 100 MB, and config.log_file_size lets you cap growth and keep logs manageable in development, test, or production.

Authentication is easy to get wrong because most users only sign in once. HTTPS with HSTS and a proven solution like Devise, Clearance or Rails primitives reduce security risks.