H2 is a full-featured, embeddable SQL database engine written in pure Java. It operates as a JDBC driver supporting both embedded (in-process) and client-server (TCP, PostgreSQL wire protocol, web console) modes. The codebase implements a complete SQL parser, query optimizer, transaction engine with MVCC, multiple storage engines (MVStore, legacy PageStore), and a rich set of data types, functions, and compatibility modes for databases like MySQL, PostgreSQL, Oracle, and MSSQLServer. It also includes tools for backup, recovery, CSV import/export, and a web-based administration console. The architecture is modular: the `org.h2.mvstore` package provides a standalone B-tree based transactional key-value store, `org.h2.value` defines a comprehensive type system, and `org.h2.expression` offers an extensible expression and function framework. The repository is exhaustively tested with thousands of SQL scripts and unit tests covering concurrency, crash recovery, and cross-database compatibility. It is actively maintained, with recent commits and support for Java 21 virtual threads and GraalVM native-image.
This repository contains the Virtuoso Open-Source multi-model database server, primarily written in C, with extensive client libraries in Java, C#, and PHP. In production, it functions as a relational database, RDF triple store, SPARQL query endpoint, XML processor, and application server (VSPX). The architecture is a monolithic server process with plugin extensions for hosting languages (CLR, Java, PHP) and connectivity via ODBC, JDBC, OLE DB, and ADO.NET. Key entry points include the Virtuoso server binary (built from libsrc/Wi/ and libsrc/Dk/), ODBC driver (binsrc/virtodbc/), JDBC Type 4 driver (libsrc/JDBCDriverType4/), and .NET client (binsrc/VirtuosoClient.Net/). Data flows include SQL parsing and execution via the Wi module, RDF/SPARQL query processing, and WebDAV/HTTP file management through the built-in web server. External dependencies include PCRE, zlib, HTML Tidy (libsrc/Tidy/), and curl. The repository also contains a suite of web applications (ODS) for blogging, bookmarks, calendar, wiki, etc., built on a common SQL-based framework, and a comprehensive test suite covering performance benchmarks (BSBM, LUBM, TPC-D/H). Despite its breadth, the codebase shows signs of age: multiple duplicate Jena driver versions, a legacy Ajax toolkit (OAT), and hardcoded paths in test scripts. It remains actively maintained with regular commits and issue triage.
This is the TigerGraph ecosystem repository, a large collection of tools, connectors, demos, benchmarks, and tutorials centered around the TigerGraph graph database platform. It is not a single application but an aggregation of community and in-house developed components. The dominant character is application: it includes production-grade ETL connectors (Spark DataSource V2, JDBC driver, Kafka Connect, Hadoop MapReduce), a multi-version GSQL CLI client, a Go-based REST API for remote GSQL management, a Kubernetes operator, and numerous demos showcasing graph analytics (PageRank, community detection, geospatial search, fraud detection, GraphRAG). There are also benchmarking suites (LDBC SNB) and sample data. The codebase exhibits high craftsmanship in the connector and client libraries, with robust retry logic, token management, streaming JSON parsing, and schema inference. However, it suffers from massive code duplication across GSQL client versions, incomplete JDBC driver implementations, hardcoded paths and credentials in demos, and outdated vendored libraries (Leaflet 0.7.7, moment-timezone 2016). Overall, it is a functional but uneven collection; the core connectors are reusable and well-engineered, while many demo scripts are fragile and require manual configuration.