docs: document ZERO_APP_ID replication slot pitfall for local dev#276
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Sriketk wants to merge 3 commits intorocicorp:mainfrom
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docs: document ZERO_APP_ID replication slot pitfall for local dev#276Sriketk wants to merge 3 commits intorocicorp:mainfrom
Sriketk wants to merge 3 commits intorocicorp:mainfrom
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Running zero-cache locally against the same Postgres as a deployed instance (e.g. via a monorepo dev script like turbo dev) causes the local instance to steal the exclusive replication slot, crashing production. Setting ZERO_APP_ID=zero_dev locally gives each environment its own slot so both can run simultaneously without conflict. Added a warning callout to the App ID section in zero-cache-config and a new "Local Development Against a Shared Database" section in deployment. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Problem
Running
zero-cachelocally against the same Postgres database as a deployed instance silently crashes production. The local instance callspg_terminate_backendto steal the exclusive replication slot, which causes the deployed zero-cache to exit. This also applies to monorepo dev scripts (e.g.turbo dev) that start zero-cache as a workspace package ifZERO_UPSTREAM_DBpoints at a shared database.This behavior is not documented anywhere in the current docs, making it very hard to debug (the deployed instance exits cleanly with code 0, not with an obvious error).
Fix
Set a distinct
ZERO_APP_IDlocally (e.g.ZERO_APP_ID=zero_dev). Zero uses the App ID to name the Postgres replication slot, so different IDs = independent slots that never conflict. No separate dev database needed.Changes
zero-cache-config.mdx: Added a warning callout under theApp IDsection explaining the pitfall and the fix.deployment.mdx: Added a new## Local Development Against a Shared Databasesection at the end with a concrete.envsnippet.Context
Discovered and debugged in a production incident where
bun dev(viaturbo dev) was running a local zero-cache workspace package pointed at production Postgres, causing the Railway-deployed zero-cache to crash repeatedly overnight.