March 2026 monthly summary for scylladb/scylladb focusing on performance and reliability improvements. Delivered targeted optimizations for tablet range side computations and lazy compaction group selection, stabilized memory usage under high load, and corrected shard-level size estimates. Resulted in measurable improvements to throughput, stability, and scalability for larger clusters.

February 2026 (scylladb/scylladb): Focused on stability, reliability, and test resilience in the storage engine. Key deliverables include: (1) Sstable compaction reliability and performance improvements to reduce hangs and improve throughput; (2) Reader concurrency semaphore stability fix to correctly surface aborted permits and avoid assertion failures; (3) Test stability improvement by lowering the disk-utilization threshold to reduce flaky test runs. These changes enhance operational stability under high load, shorten maintenance cycles, and improve confidence in automated tests.

January 2026 — Delivered significant reliability and performance improvements in scylladb/scylladb. Key features include hardening of the tablet state machine with barrier-free cleanup_target transitions and a new write_both_read_old_fallback_cleanup state; expanded concurrency/admission controls with preemptive_aborted and preemptive_abort_factor and stricter waiters validation; topology_coordinator improvements enabling cleanup_target transitions without extra barriers in streaming/rebuild_repair and post-write_both_read_old failures. Start_writes gained retry logic for verification reads and enhanced failure logging. Testing framework refinements sped up CI (pytest fixture fixes, shorter OOS tests, reduced volumes). Overall impact: fewer flaky reads, more robust transitions, faster and more observable failures, and quicker development feedback.

December 2025 monthly summary for scylladb/scylladb focusing on delivering business value through resilience, reliability, and performance improvements across tablet migration, writes, and load balancing. The month focused on hardening the test suite to reflect real-world failure scenarios, stabilizing write paths under node outages, and improving tablet allocation distribution to prevent skew. The work culminated in higher cluster stability, lower risk of write failures during outages, and more predictable allocation behavior across shards.

November 2025: Focused on reliability and correctness of shard routing for group0 operations in scylladb/scylladb. Delivered a targeted bug fix to ensure mark_excluded executes only on shard0 and to redirect cross-shard requests to shard0, preventing incorrect shard operations. The fix strengthens data integrity and operation isolation for group0, reducing the risk of inconsistent routing in distributed storage services. Commit 0ed34527215dbffd226fc0f60d5e90cb6a089fba implements the change in service/storage_service: Mark nodes excluded on shard0, including the redirect logic and safeguards. This work reduces the potential for incorrect group0 operations in multi-shard deployments and enhances overall system resilience.

October 2025 monthly work summary for scylladb/scylladb focusing on reliability and startup robustness. Delivered two main improvements: 1) Disk Space Monitoring Reliability Improvement with logging refactor to separate request and activation messages, reducing race-condition-driven test flakiness and improving reliability of disk space monitoring. 2) Startup Robustness: Ignore Inaccessible Files During Verification to prevent startup failures when files are removed during verification, especially in environments using FUSE-backed volumes. These changes strengthen production reliability in disk-space constrained deployments and reduce CI instability.

September 2025: Focused on stabilizing storage-related testing and expanding infrastructure for robust coverage in scylladb/scylladb. Consolidated flaky tests, improved test setup and disk-space monitoring, and hardened volume test workflows. Updated toolchain and dependencies to improve CI reliability and enable non-privileged test execution. The work enhances test determinism under 3-node RF=3 scenarios and tightens coverage around out-of-space prevention and tablet split/compaction behavior.

Monthly summary for 2025-08 focused on scylladb/scylladb, highlighting the delivery of a new Disk Space Monitor Subscription API and its business value. No major bugs fixed this month based on provided data.

July 2025: Delivered two major resilience features for ScyllaDB, with a focus on maintaining availability and controlling operational load under disk-space pressure. Implemented Dynamic Repair Service Control to allow temporary disabling of local repair tasks while honoring global repair requests, enabling multiple enable/disable cycles, and preventing repairs when disk space is critically low with retrying later. Implemented Disk Space Aware Compaction Management by subscribing the compaction manager to the disk space monitor, so that under low space it drains operations and re-enables when space recovers. These changes reduce risk of cascading failures and stabilize performance in constrained environments, improving overall reliability and capacity management.

Summary for 2025-06: Key features delivered: - Robust concurrent disable/enable semantics for the compaction manager, replacing separate 'enabled'/'disabled' states with a single 'running' state and a disable counter to safely support multiple concurrent disable requests; the manager is enabled only when the counter reaches zero. Commits: 40c40be8a611a2313d343abbb94b80810ee0d03b. - Per-node critical disk utilization flag added to TABLE_LOAD_STATS and related troubleshooting; extended locator::load_stats reporting, storage_service integration, and accompanying documentation. Commits: 54201960e670cebd89e763f7f839dbf1eb2405f5; c2de678a87c450bc2fdd5d4f28d2a528693b203f. Major bugs fixed: - Test correctness: fix compaction history time window computation; corrected time window calculations and ensured timestamps propagate to CQL statements, resolving mis-spread data across time windows and improving sstable generation and tombstone testing. Commit: a22d1034affcb08f56e900fe3c8a78a4a951916f. Overall impact and accomplishments: - Improved robustness of the compaction manager under concurrent requests, reducing race conditions and operational risk. - Enhanced observability and troubleshooting capabilities with per-node disk utilization reporting and improved documentation. - Strengthened test coverage for time-windowed compaction logic, improving data correctness and regression safety. Technologies/skills demonstrated: - Advanced concurrency control and state-machine design for distributed components. - RPC interface evolution and per-node metrics instrumentation. - Documentation, troubleshooting guidance, and test engineering to reduce deployment risk and accelerate remediation.

May 2025 monthly summary focused on delivering disk utilization safeguards to harden cluster stability and data integrity under capacity pressure. Implemented safeguards to prevent instability from data migrations when replicas reach critical disk utilization, including flows to move tablets to a cleanup state and deferring new migrations via the load balancer until conditions are safe. Introduced a critical_disk_utilization mode that blocks non-essential mutations on user-related tables when disk space is critically low, in conjunction with a disk space monitor to protect data integrity. These changes, combined with proactive resource governance, lay the groundwork for safer migrations, improved SLA adherence, and more predictable performance during capacity pressure.

April 2025 monthly summary for scylladb/scylladb focusing on delivering business-value through improved test coverage, reliability, and operational hygiene.

March 2025 Monthly Summary (scylladb/scylladb) Overview: Focused on improving reliability of disk-heavy write paths and enhancing nodetool robustness. Delivered a new failure-handling feature for disk utilization and fixed a nodetool crash related to missing rows_merged, with tests updated to cover edge cases. Key achievements (top 3-5): - Disk Utilization Write Failure Handling: Introduced a new custom exception critical_disk_utilization_exception for scenarios where user table mutation writes are blocked by critical disk utilization, and integrated into coordinator exception handling to surface meaningful disk-related write errors. Commit: 132fd1e3f2867e1cbe80ada7ea79c9b2195e47ab - Nodetool compactionhistory stability: Fixed crash when rows_merged is null or an empty list by ensuring an empty list is produced and updated tests accordingly. Commit: 113647550f1aaae0cb1529d4c17d6a7b34825702

February 2025: Delivered Critical Disk Utilization Threshold Configuration in scylladb/scylladb. Introduced a new configuration option 'critical_disk_utilization_level' with a default of 98% to trigger defensive measures (such as rejecting user writes) when disk usage approaches capacity. The change is implemented via commit 535c901e507a53021cb129f19047bf5856e50334. No major bugs fixed this month. Impact: reduces risk of service outages due to disk pressure and improves data safety; prepares for automated capacity management. Technologies/skills demonstrated: configuration management, defensive programming, capacity planning, code hygiene and review.

January 2025: Delivered targeted fixes and a foundational refactor in scylladb/scylladb. Reduced API surface by removing an unimplemented truncate endpoint, improved keyspace telemetry, and simplified a critical concurrency path for better performance under load. Applied concrete changes with precise commits and added tests to prevent regressions. Business impact includes reduced maintenance overhead, clearer observability, and more robust operation under concurrent workloads.

December 2024 monthly summary for scylladbbot/scylla-cluster-tests focusing on reliability improvements in the Latte feature tests.

November 2024 — Highlights: Implemented a timeout-aware admission check for the reader concurrency path to prevent wasted work on reads that timeout under overload; extended compaction logging to include shard ID, compaction type, start/end times, and input/output sstable lists for better observability. These changes reduce wasted compute, stabilize latency under high load, and accelerate troubleshooting and capacity planning.

During October 2024, two high-impact features were delivered for scylladb/scylladb: 1) SSTable metadata UDT integration with compaction history, introducing a new sstableinfo_type to store generation UUID, origin, and size, and recording this metadata in system.compaction_history to trace compacted files and outcomes; 2) Enhanced compaction history diagnostics and tombstone purge statistics, including new diagnostic columns, API/return types, and richer nodetool output to expose tombstone purge attempts and failures. These changes provide deeper observability, enabling faster issue diagnosis, more accurate capacity planning, and stronger data lifecycle tracking. The work was completed through targeted schema migrations, API enhancements, and instrumentation across system_keyspace, compaction_garbage_collector, mutation_compactor, compacting_reader, compaction, and nodetool components.