Understanding Raima Database Manager Architecture

In-Memory and Disk Persistence

RDM allows hybrid operation using both RAM and persistent storage. This duality demands strict control over flushing, checkpoints, and system calls to avoid inconsistencies during crashes or power interruptions.

Multi-Model Access

Developers can use SQL queries or navigational access through C/C++ APIs. While flexible, misuse of these paradigms together without synchronization may introduce logic errors or race conditions.

Common Issues in Production

1. Transaction Deadlocks

Concurrent transactions on overlapping records can lead to circular wait conditions. Without proper lock timeout settings, these can freeze the system or rollback valid operations.

2. Data Corruption After Power Failure

Unexpected shutdowns during write-heavy operations may corrupt journaled data if not properly flushed or checkpointed. Recovery may not be possible without rollback logs.

3. Multi-threaded Access Violations

Improper handling of sessions and database handles across threads causes undefined behavior, often manifesting as segmentation faults or lost transactions.

4. Schema Evolution Constraints

RDM supports limited online schema changes. Adding indexes or altering fields on live databases may require application restarts or export/import cycles.

5. Embedded Platform Integration Failures

RDM on RTOS or constrained environments may fail due to missing file system support, thread limitations, or memory allocation mismatches.

Diagnostics and Debugging Techniques

Enable Verbose Logging

• Set log level to RDM_LOG_DEBUG and capture logs to a persistent storage area. Logs include API errors, transaction steps, and memory usage.
• Use d_explain() and sql_diagnostic() to retrieve low-level failure reasons programmatically.

Monitor Deadlocks and Lock Contention

• Use the rdm_stats() API to capture lock acquisition delays and wait queue sizes.
• Simulate transaction overlap scenarios in staging to reproduce and tune lock timeout thresholds.

Validate Crash Recovery Mechanism

• Ensure rdm_recover() is called during initialization. Verify .jrn and .rcv files are intact and flushed correctly before crashes.
• Inject failure during writes to test durability using watchdog timers or simulated resets.

Test Thread Safety of Handles

• Assign separate sessions per thread or use mutex wrappers. Avoid reusing handles across thread boundaries.
• Review code for race conditions involving cursor movement or record updates.

Audit Schema Changes

• Use RDM Workbench to simulate schema migration. Document all changes using DDL logs.
• Back up and restore databases between schema changes using rdm_export() and rdm_import() to avoid breaking production instances.

Step-by-Step Fixes

1. Resolve Transaction Deadlocks

• Set RDM_SET_LOCK_TIMEOUT to enforce transaction rollback on long waits.
• Adopt a consistent lock acquisition order and avoid user-defined nested transactions when possible.

2. Prevent Data Corruption After Power Loss

• Use RDM_FLUSH_EVERY_COMMIT to enforce fsync on commit. Enable battery-backed RAM on embedded systems where possible.
• Test recovery using rdm_recover() after kill signals or simulated resets.

3. Fix Multi-Thread Access Violations

• Use thread-local storage (TLS) for RDM handles. Protect shared state with semaphores or condition variables.
• Avoid global session handles unless wrapped in synchronization logic.

4. Handle Schema Evolution Safely

• Freeze writes during schema migration. Export and re-import data to apply structural changes safely.
• Use versioning in schema files and validate at application startup.

5. Integrate RDM on Embedded Targets

• Ensure file system APIs (open, read, write) are available. Link against correct libc versions or RTOS abstraction layers.
• Statically allocate memory if heap fragmentation causes allocation failures.

Best Practices

• Use journaling and checkpointing consistently to maintain ACID compliance under load.
• Allocate one session per thread and avoid shared cursors.
• Batch writes and commit in intervals to reduce fsync overhead on flash memory.
• Validate all API return codes and use d_errorstr() for detailed diagnostics.
• Simulate failure scenarios in test environments to validate recovery paths and tune rollback behavior.

Conclusion

Raima Database Manager delivers exceptional performance for embedded and real-time workloads but requires disciplined memory, thread, and transaction management. By enforcing thread safety, auditing recovery logic, and applying structured schema changes, developers can ensure robustness, data durability, and consistency in RDM-powered systems operating at the edge.

FAQs

1. What causes RDM to deadlock during transactions?

Concurrent transactions modifying overlapping records without proper lock ordering. Use lock timeouts and serialize access when needed.

2. How can I recover after a crash?

Use rdm_recover() on startup and ensure journal files are preserved and flushed at commit time.

3. Is RDM thread-safe by default?

No. You must assign a separate session per thread and avoid sharing handles unless synchronized explicitly.

4. Can I change schema without downtime?

Minor changes may be possible, but structural updates typically require export, schema update, and re-import cycles.

5. Why does RDM fail to initialize on my RTOS?

File system or memory allocation functions may be missing. Validate libc linkage and configure memory models to match RDM requirements.