Apache Calcite vs PlyDB

Apache Calcite is a free, open-source data management framework for applications that need database-management components without built-in storage. It provides an industry-standard SQL parser, validator, and JDBC driver. Queries are represented as relational algebra, then transformed with planning rules and a cost model for optimization. Calcite can mediate between applications and several storage locations or processing engines, and can push computation to a source database. Listed adapters include Arrow, Cassandra, CSV, Druid, Elasticsearch, JDBC, MongoDB, Redis, Spark, and Splunk. Its JDBC driver supports local connections and remote connections using JSON over HTTP or Protobuf over HTTP. Calcite is available as source and through Maven, for API or self-hosted use. Build prerequisites include Git and Java JDK 8u220 or later, with Java 11 preferred. It does not store data; each source must be registered through a schema or adapter.

PlyDB has no write-up on Specifiction yet; its figures are above.