Opik Backend

Architecture

• Layered: Resource → Service → DAO (never skip layers)
• DI: Guice modules, constructor injection with @Inject
• Databases: MySQL (metadata, transactional) + ClickHouse (analytics, append-only)

Critical Gotchas

StringTemplate Memory Leak

// ✅ GOOD
var template = TemplateUtils.newST(QUERY);

// ❌ BAD - causes memory leak via STGroup singleton
var template = new ST(QUERY);

List Access

// ✅ GOOD
users.getFirst()
users.getLast()

// ❌ BAD
users.get(0)
users.get(users.size() - 1)

SQL Text Blocks

// ✅ GOOD - text blocks for multi-line SQL
@SqlQuery("""
        SELECT * FROM datasets
        WHERE workspace_id = :workspace_id
        <if(name)> AND name like concat('%', :name, '%') <endif>
        """)

// ❌ BAD - string concatenation
@SqlQuery("SELECT * FROM datasets " +
        "WHERE workspace_id = :workspace_id " +
        "<if(name)> AND name like concat('%', :name, '%') <endif> ")

Immutable Collections

// ✅ GOOD
Set.of("A", "B", "C")
List.of(1, 2, 3)
Map.of("key", "value")

// ❌ BAD
Arrays.asList("A", "B", "C")

Error Handling

Use Jakarta Exceptions

throw new BadRequestException("Invalid input");
throw new NotFoundException("User not found: '%s'".formatted(id));
throw new ConflictException("Already exists");
throw new InternalServerErrorException("System error", cause);

Error Response Classes

• Simple: io.dropwizard.jersey.errors.ErrorMessage
• Complex: com.comet.opik.api.error.ErrorMessage
• Never create new error message classes

Logging

Format Convention

// ✅ GOOD - values in single quotes
log.info("Created user: '{}'", userId);
log.error("Failed for workspace: '{}'", workspaceId, exception);

// ❌ BAD - no quotes
log.info("Created user: {}", userId);

Never Log

• Emails, passwords, tokens, API keys
• PII, personal identifiers
• Database credentials

Reference Files

• clickhouse.md – ClickHouse query patterns
• mysql.md – TransactionTemplate patterns
• testing.md – PODAM, naming, assertion patterns
• migrations.md – Liquibase format for MySQL/ClickHouse