Engineering Blog

Engineering deep-dives from the SlashFeed team — Elixir, Phoenix, and how the product is built.

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Zero-write upserts in Ecto with IS DISTINCT FROM

A plain ON CONFLICT DO UPDATE writes the row even when nothing changed — every feed poll rewrites thousands of identical entries, bumping updated_at and burning WAL. One SQL clause, IS DISTINCT FROM, makes Postgres skip the no-op write. The catch: when it skips, RETURNING returns nothing and Ecto raises StaleEntryError. Here is the full pattern, the rescue trick that turns the error into an :unchanged result, and the three-layer RSS dedup strategy it sits inside.

Jul 13, 2026

elixir ecto postgresql upsert rss performance

Preventing duplicate RSS entries with content hashing

How SlashFeed prevents duplicate RSS entries through a three-layer strategy: GUID uniqueness, SHA-256 content hashing, and a PostgreSQL IS DISTINCT FROM guard that eliminates no-op writes on every fetch cycle.

Jul 5, 2026

elixir phoenix postgresql ecto rss performance

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