Database Technology

Percona Server for MySQL 9.7.2-2 introduces DISTANCE() and VECTOR_DISTANCE() functions, enabling direct vector similarity scoring within SQL queries. The release supports COSINE, EUCLIDEAN, MANHATTAN, and DOT metrics, allowing developers to rank or filter embeddings without external services. This serves as a foundational compute primitive for in-database vector operations.

• SQL-native vector scoring eliminates need for external vector DBs for simple similarity tasks.
• Supports COSINE, EUCLIDEAN, MANHATTAN, and DOT distance metrics for flexible ranking.
• ANN indexing like HNSW is noted as a future milestone for large-scale performance.

PgBouncer 1.26.0 addresses three critical denial-of-service vulnerabilities affecting unauthenticated connections and malicious servers, specifically targeting SCRAM authentication logic and packet buffer handling. The release introduces default tracking for search_path and default_transaction_read_only, while adding a new pool_idle_timeout configuration option. Additionally, it enables per-user and per-database query_wait_timeout settings, adopts the meson build system, and removes the deprecated online restart flag.

• Patch immediately to mitigate DoS risks from unauthenticated clients and malicious backends
• Utilize new pool_idle_timeout to manage connection lifecycle and resource consumption
• Adopt meson build for modern compilation workflows replacing older methods
• Leverage granular query_wait_timeout controls at user and database levels
• Remove usage of deprecated -R flag for online restarts in maintenance scripts

A recent observation shows forty DELETE statements vanished from pg_stat_statements because the view hit its default 5,000 entry limit. The eviction mechanism discards the least-executed statements, causing one-off operations to be pruned immediately when new, more frequent queries arrive. This behavior is documented and intentional, driven by the need to accommodate higher-volume traffic in the fixed-size hash table.

• Single-run DELETEs often disappear from stats if they are the least executed statements.
• The default 5,000 entry limit is small for high-cardinality workloads with many unique queries.
• Eviction is based on execution count, so one-time maintenance tasks are easily discarded.
• Monitor pg_stat_statements_info.dealloc to track how many entries have been removed.
• Consider increasing max_statements if tracking rare but critical operations is necessary.

An attempt to back up a promoted standby using pgBackRest failed because archive_mode was off, despite disabling the archive-mode-check flag. Modifying the source code bypassed the error, but the resulting backup integrity remains unverified. The author advises sticking to supported configurations like a restart or controlled switchover rather than relying on this unsupported workaround.

• Disabling archive-mode-check=n does not enable actual WAL archiving on the standby.
• Source code modifications can bypass errors but do not guarantee backup consistency.
• Avoid promoting standbys with archive_mode=off if immediate backup is required.
• Use controlled switchover or restart to ensure archive_mode is enabled properly.

ClickHouse has released WalShadow, a tool that replicates PostgreSQL data into ClickHouse by reading the physical WAL stream directly. Instead of relying on logical decoding, it decodes heap records itself and writes ClickHouse-native blocks. This approach aims to reduce overhead and complexity associated with standard logical replication pipelines.

• Bypasses logical decoding to reduce CPU and I/O overhead on the source PostgreSQL server
• Reads the physical WAL stream, similar to how streaming replicas operate
• Decodes heap records internally to generate ClickHouse-native data blocks
• Offers an alternative to standard logical replication for specific sync use cases