What Oracle 18c Sharding and MySQL 8.0 Reveal About Modern Database Evolution

Oracle High Availability and Sharding (12c → 18c)

Oracle’s Maximum Availability Architecture (MAA) has been refined for 16 years, evolving from 9i to the current 18c release. In 18c the RAC Sharding 2.0 replaces the earlier hash‑based sharding model. Each RAC instance can act as an independent shard, so adding nodes yields linear performance growth. Geographic replication and richer partitioning strategies extend sharding to multi‑region deployments.

Active Data Guard in 18c introduces a nologging option for bulk‑load operations, delivering higher throughput while preserving HA guarantees. The Data Guard broker’s validate feature can automatically repair configuration drift, supporting autonomous management.

Online DDL now supports fine‑grained changes down to partition and sub‑partition levels, but fully autonomous patching requires the combined RAC + Multitenant + Active Data Guard stack.

MySQL 8.0 Core Improvements

MySQL 8.0 removes MyISAM entirely, making InnoDB the sole default storage engine. The data dictionary is now a true transactional component, yielding large metadata‑access speedups (e.g., queries on 5 000 tables vs. 1 000 000 tables). Default character set is utf8mb4.

Security enhancements include role‑based privilege packaging, removal of the unrestricted SUPER privilege, and a warning for the insecure --skip-grants option.

The long‑standing auto‑increment bug that could generate duplicate keys after a node restart is finally fixed.

Configuration tuning is simplified with a single auto‑tune parameter that adjusts several related settings automatically.

Undo handling has been refined across versions; 8.0 now supports shrink‑and‑grow behavior with better performance.

Invisible indexes allow index creation without affecting existing queries, useful for gradual rollout of new indexes.

Online backups are enabled by the new statement LOCK INSTANCE FOR BACKUP (released with UNLOCK INSTANCE), preventing snapshot inconsistency during DML.

Histograms are now collected at column granularity, providing the optimizer with richer statistics for more accurate query plans.

performance_schema has been optimized; with 1 000 active sessions, response time in 8.0 is significantly lower than in 5.7.

Default configuration values have been tuned to “optimal” settings, and the legacy query cache has been removed in favor of external solutions such as ProxySQL.

MySQL 8.0 Development Features and PostgreSQL Comparison

New DML syntax SKIP LOCKED helps avoid hotspot contention by skipping rows that are already locked.

Index definitions now support per‑column sort order (ASC/DESC) and multi‑column indexes, giving finer control over index behavior.

MySQL 8.0 adds experimental JSON support and full Common Table Expression (CTE) implementation, including recursive queries.

Window functions are available, enhancing analytical workloads.

GIS capabilities have been expanded; in some benchmarks MySQL’s spatial functions outperform PostgreSQL’s.

Percona’s comparative performance tests (see https://mp.weixin.qq.com/s?__biz=MzI4NTA1MDEwNg==∣=2650759598&idx=1&sn=b42b27249e69a5cbaa7769cc3818e172) show that MySQL 8.0 delivers substantial improvements under heavy load.