Database Technology

Percona Toolkit’s pt-online-schema-change uses dynamic chunk sizing to adapt to production workloads during large table migrations. However, this auto-resize mechanism can backfire when used with Galera clusters, potentially triggering flow control issues. The article explains how the interaction between chunk growth and Galera replication mechanics can create counterproductive performance bottlenecks.

• pt-osc chunk auto-resize is designed for workload adaptation but may harm Galera clusters.
• Dynamic chunk growth can trigger Galera flow control, stalling replication.
• Monitor Galera flow control metrics when running pt-osc on large tables.
• Consider limiting chunk size or using alternative tools for Galera environments.

Amazon DocumentDB engine version 8.0.2 now supports retryable writes, allowing the MongoDB driver to automatically retry write operations once during transient errors like network interruptions or primary failovers. This capability is enabled by default in most current drivers, removing the need for applications to set retryWrites=false in the connection string. The feature applies to all write commands except updateMany, significantly improving application resilience without requiring code changes.

• Upgrade to DocumentDB engine 8.0.2 to enable retryable writes support.
• Drivers automatically retry writes on transient errors, boosting resilience.
• No code changes needed; drivers handle retries by default.
• Remove retryWrites=false from connection strings to avoid conflicts.
• Not supported for updateMany commands.

Amazon DocumentDB version 8.0.2 introduces retryable writes for transient errors, enhancing resilience during failovers. The release adds support for five new aggregation stages, including $setWindowFields, $bucketAuto, $facet, $graphLookup, and correlated $lookup. These updates expand MongoDB API compatibility and improve query performance for advanced analytics and hierarchical queries.

• Retryable writes auto-retry transient errors, reducing manual error handling in apps.
• New aggregation stages enable window functions, faceted search, and graph traversal.
• Change stream enhancements improve real-time data synchronization capabilities.
• Higher MongoDB compatibility simplifies migration without code changes.
• Version 8.0.2 supports correlated $lookup for complex join operations.

Percona highlights how high-volume write workloads in PostgreSQL can trigger excessive autovacuum cycles and table bloat, leading to severe performance degradation. To mitigate this, the article introduces PgQ and PgQue as workflow engines designed to decouple and manage these frequent updates more efficiently. These tools help stabilize the database by handling write spikes that would otherwise overwhelm standard vacuum processes.

• High-frequency writes cause excessive autovacuum runs and table bloat in PostgreSQL.
• PgQ and PgQue serve as workflow engines to manage these heavy update loads.
• Decoupling updates improves concurrency and prevents unmanageable database states.
• These tools are relevant for production environments with millions of daily updates.
• Consider these engines if standard autovacuum cannot keep up with write volume.