What is a metastore?
Metastores are a critical component for Athena. Metastores tell Athena which datasets are available for it to query and how to process the underlying data. When a user submits a SQL statement to Athena for execution, Athena parses the query's text, identifies the tables and columns needed, and looks up a description of them from the metastore. Once it knows where the data lives, how it is stored, and the format, Athena requests the data, interprets it, and executes the query.
The metastore also serves as a directory of available datasets that can be queried. Datasets are represented by tables stored in databases, although in this context, the terms tables and databases do not refer to physical databases or tables. We refer to tables and databases as metadata, data that describes other data, and metastores store metadata. In the big data space, analytics engines usually store metadata and data separately. Athena's most common metastore is AWS Glue...
