Where does Hadoop Hcatalog store databases and tables?

Question

I am new to Hadoop. I have been doing the following tutorial based on a prebuilt Hadoop virtual machine running on Linux.

hadoop tutorial

I did create a Hcatalog table on the default database based on a file. I would like to know if those databases and tables can be seen on the Hadoop filesystem or if they are on some kind of special store.

Answer 1

HCatalog is built on top of the Hive metastore so where it stores it's metadata will depend on how you have hive set up. If you are using an external database for your metastore it will be there if you are using the default configuration it is stored in a local derby database. You woun't be able to see the "databases and tables" on the hadoop filesystem. Hive provides a mechanism to project structure onto this data (which is on hdfs) and query the data using a SQL-like language called HiveQL.

https://cwiki.apache.org/confluence/display/Hive/HCatalog+UsingHCat

Answer 2

HCatalog creates a table abstraction layer over data stored on an HDFS cluster. This table abstraction layer presents the data in a familiar relational format and makes it easier to read and write data using familiar query language concepts.

HCatalog data structures are defined using Hive's data definition language (DDL) and the Hive metastore stores the HCatalog data structures. Using the command-line interface (CLI), users can create, alter, and drop tables. Tables are organized into databases or are placed in the default database if none are defined for the table. Once tables are created, you can explore the metadata of the tables using commands such as Show Table and Describe Table. HCatalog commands are the same as Hive's DDL commands.

Please refer When to use Hcatalog and what are its benefits for more clarification.

Please refer Microsoft Big Data Solution to know more about HCatalog.