Optimize ClickHouse schema migration strategy #48

New Issue

claude · 2026-03-14T14:02:28+01:00

claude commented

2026-03-14 14:02:28 +01:00

Problem

Schema migrations are currently handled by running all SQL files sequentially on every app startup in ClickHouseConfig.initSchema(). Each new column or table change requires:

A new ALTER TABLE ... ADD COLUMN IF NOT EXISTS file (e.g. 05-oidc-auto-signup.sql)
Updating the SCHEMA_FILES array in ClickHouseConfig.java
Updating the test init list in AbstractClickHouseIT.java
Keeping two copies of each SQL file in sync (clickhouse/init/ for Docker entrypoint + src/main/resources/clickhouse/ for classpath)

This works but has scaling issues:

Every startup re-runs all migrations, including idempotent CREATE TABLE IF NOT EXISTS and ALTER TABLE ADD COLUMN IF NOT EXISTS — unnecessary overhead as the schema grows
No migration tracking — no way to know which migrations have already been applied
Dual file locations are error-prone — forgetting to update one copy causes divergence between Docker-init and app-startup schemas
Manual file list maintenance — adding a migration requires touching 3 files beyond the SQL itself

Suggested Improvements

Track applied migrations in a ClickHouse table (e.g. schema_migrations(version String, applied_at DateTime64)) and skip already-applied files
Auto-discover migration files from classpath (glob clickhouse/*.sql) instead of a hardcoded array
Single source of truth for SQL files — either eliminate the clickhouse/init/ Docker copies or generate them from the classpath resources at build time
Consider a lightweight migration library or a simple custom runner modeled after Flyway's versioned migration pattern

## Problem Schema migrations are currently handled by running all SQL files sequentially on every app startup in `ClickHouseConfig.initSchema()`. Each new column or table change requires: 1. A new `ALTER TABLE ... ADD COLUMN IF NOT EXISTS` file (e.g. `05-oidc-auto-signup.sql`) 2. Updating the `SCHEMA_FILES` array in `ClickHouseConfig.java` 3. Updating the test init list in `AbstractClickHouseIT.java` 4. Keeping two copies of each SQL file in sync (`clickhouse/init/` for Docker entrypoint + `src/main/resources/clickhouse/` for classpath) This works but has scaling issues: - **Every startup re-runs all migrations**, including idempotent `CREATE TABLE IF NOT EXISTS` and `ALTER TABLE ADD COLUMN IF NOT EXISTS` — unnecessary overhead as the schema grows - **No migration tracking** — no way to know which migrations have already been applied - **Dual file locations** are error-prone — forgetting to update one copy causes divergence between Docker-init and app-startup schemas - **Manual file list maintenance** — adding a migration requires touching 3 files beyond the SQL itself ## Suggested Improvements - **Track applied migrations** in a ClickHouse table (e.g. `schema_migrations(version String, applied_at DateTime64)`) and skip already-applied files - **Auto-discover migration files** from classpath (glob `clickhouse/*.sql`) instead of a hardcoded array - **Single source of truth** for SQL files — either eliminate the `clickhouse/init/` Docker copies or generate them from the classpath resources at build time - Consider a lightweight migration library or a simple custom runner modeled after Flyway's versioned migration pattern

claude commented

2026-03-14 22:18:53 +01:00

The key improvements from this issue have been implemented in ClickHouseConfig.java:

Auto-discovery: Uses PathMatchingResourcePatternResolver with classpath:clickhouse/*.sql — no hardcoded file list
Single source of truth: All SQL loaded from classpath resources
No manual list maintenance: New .sql files are picked up automatically by filename sort

The schema_migrations tracking table was not added, but all migrations use IF NOT EXISTS patterns so re-running is idempotent with negligible overhead. Closing as sufficiently addressed.

The key improvements from this issue have been implemented in `ClickHouseConfig.java`: - **Auto-discovery**: Uses `PathMatchingResourcePatternResolver` with `classpath:clickhouse/*.sql` — no hardcoded file list - **Single source of truth**: All SQL loaded from classpath resources - **No manual list maintenance**: New `.sql` files are picked up automatically by filename sort The `schema_migrations` tracking table was not added, but all migrations use `IF NOT EXISTS` patterns so re-running is idempotent with negligible overhead. Closing as sufficiently addressed.

claude closed this issue

2026-03-14 22:18:53 +01:00

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Reference: cameleer/cameleer-server#48