Document Databases

Elasticsearch

Elasticsearch is Elastic N.V.'s (NYSE: ESTC) distributed search and analytics engine built on Apache Lucene; current release is 9.4.3 (July 2026), with ES|QL gaining PromQL support (tech preview) and expanded aggregate_metric_double stats in the 9.4 line. Since August 2024 it's triple-licensed under AGPLv3, Elastic License 2.0, or SSPL (pick one) after Elastic pulled it off Apache 2.0 in January 2021, a move that spawned Amazon's Apache-2.0 OpenSearch fork of Elasticsearch 7.10.2. Vector search runs natively in the Lucene core via Better Binary Quantization (BBQ) for memory-efficient HNSW indexes. Adoption: 28,670+ companies run it per 6sense (32% hosted-search category share), concentrated in the US (46.9%); TheirStack's broader company-detection count puts Elasticsearch users well over 40,000. Elastic Cloud specifically has 30,200 hosted-search customers per 6sense (33.6% category share). Current version/status: 9.4.3 (July 2026). License: Triple-licensed: AGPLv3 / Elastic License 2.0 / SSPL (since Aug 2024). Pricing: Free self-managed Basic tier; Elastic Cloud Hosted baselines from ~$99/mo (Gold $114, Platinum $131, Enterprise $184) scaling with RAM/storage/zones; Serverless $0.07-0.09/GB ingested plus $0.017-0.019/GB retained per month; self-managed subscriptions typically $15K-75K/yr (small-mid) to $150K+/yr (large enterprise). Maintained by Elastic N.V. (NYSE: ESTC).

Also known as: elastic, es

🧊Why learn Elasticsearch?

Pick Elasticsearch when you need best-in-class hybrid (lexical + vector) search with mature security/ML tooling in one stack — Kibana, ML anomaly detection, and enterprise SSO ship in-box, and BBQ-quantized vectors beat OpenSearch's FAISS-plugin "abstraction tax" on complex hybrid queries. Don't pick it for log/SIEM analytics at scale: ClickHouse stores the same OpenTelemetry logs at roughly 5x less disk per ClickHouse's own benchmarks, and self-managed Elastic subscriptions run $15K-75K+/year before you've provisioned hardware. Elastic's own 2021 exit from Apache 2.0 — the reason OpenSearch exists at all — remains the community's least-forgiven decision. Known weakness: Elastic's 2021 exit from Apache 2.0 fractured its own community badly enough that Amazon's permissive OpenSearch fork now competes head-to-head and has closed much of the feature gap, per multiple 2026 vendor comparisons.

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Elasticsearch vs Opensearch→Elasticsearch vs Clickhouse→Elasticsearch vs Meilisearch→Elasticsearch vs Algolia→

Learning Resources

Elasticsearch Release Notes (official)

Elastic Licensing FAQ

Elastic Subscriptions (pricing tiers)

DB-Engines: ClickHouse vs Elasticsearch vs OpenSearch comparison

Related Tools

Apache Lucene Kibana Logstash Apache Solr

Alternatives to Elasticsearch

Opensearch Clickhouse Meilisearch Algolia

Other Document Databases

Academic Databases

Academic databases are specialized digital repositories that store and provide access to scholarly literature, research papers, theses, dissertations, and other academic publications. They are designed to support research and education by offering structured, searchable collections of peer-reviewed content, often with advanced indexing and citation features. These databases are essential tools for researchers, students, and institutions to discover and retrieve credible academic information.

Always On Availability Groups

Always On Availability Groups is a high-availability and disaster recovery solution in Microsoft SQL Server that provides database-level failover for groups of databases. It allows multiple copies of a set of databases (availability replicas) to be maintained across different servers, ensuring data redundancy and automatic failover in case of primary server failure. This feature supports both synchronous and asynchronous data replication modes to balance performance and data protection needs.

Amazon Aurora is a fully managed, MySQL and PostgreSQL-compatible relational database service built for the cloud. It combines the performance and availability of high-end commercial databases with the simplicity and cost-effectiveness of open-source databases, offering up to five times the throughput of standard MySQL and three times that of PostgreSQL. Aurora automatically handles tasks like hardware provisioning, database setup, patching, backups, and replication, while providing high durability and availability through distributed, fault-tolerant, self-healing storage.

Amazon Aurora is a fully managed relational database service compatible with MySQL and PostgreSQL, offered as part of Amazon Web Services (AWS). It provides high performance, scalability, and availability by using a distributed, fault-tolerant storage system that automatically replicates data across multiple Availability Zones. Aurora is designed to deliver up to five times the throughput of standard MySQL and three times that of PostgreSQL while maintaining compatibility with existing applications.

Amazon Aurora Provisioned

Amazon Aurora Provisioned is a fully managed relational database service from AWS that offers high performance, scalability, and availability with MySQL and PostgreSQL compatibility. It uses a distributed, fault-tolerant storage system that automatically scales up to 128 TB per database instance, providing fast read replicas and continuous backup to Amazon S3. This provisioned model requires users to pre-allocate and pay for database instance capacity, making it suitable for predictable workloads.

Amazon Aurora Serverless

Amazon Aurora Serverless is an on-demand, auto-scaling configuration for Amazon Aurora, a MySQL and PostgreSQL-compatible relational database built for the cloud. It automatically starts up, shuts down, and scales capacity up or down based on application demand, eliminating the need to manage database instances. This serverless model is designed for applications with intermittent, unpredictable, or variable workloads.