Download Hologres JDBC Driver

Download the Hologres JDBC driver, copy the JDBC URL into DbSchema, and start designing schemas with ER diagrams — free Community Edition.

About the Hologres JDBC driver

A JDBC driver is a Java .jar library that lets applications connect to Hologres. DbSchema uses JDBC to reverse engineer schemas, run SQL, and generate documentation. Driver files are usually published by the database vendor or an open-source project.

JDBC URL format

Host, port, database name, and SSL options are passed in a URL starting with jdbc:. Each Hologres driver uses its own syntax — see the connection details below.

The Hologres JDBC driver

Alibaba Cloud Hologres is a Hybrid Serving and Analytical Processing (HSAP) warehouse that answers point lookups and analytical scans from one copy of the data. It speaks the PostgreSQL wire protocol, so the standard PostgreSQL JDBC driver connects to it, and it adds a physical design of its own: each table chooses a row or column orientation, a distribution key, a clustering key and an event time column. Hologres is used for real-time dashboards, for serving features to online applications, and as the query layer over data held in MaxCompute.

The Hologres JDBC URL

• Required File(s): postgresql-xxx.jar
• Java Driver Class: org.postgresql.Driver
• JDBC URL: jdbc:postgresql://{HOST}:80/{DB}
• Website: Alibaba Cloud Hologres

Hologres is compatible with PostgreSQL 11, so tables, views, functions and foreign keys are read through the standard PostgreSQL catalog. The endpoint listens on port 80 rather than on PostgreSQL's 5432, and the physical design of each table is kept in the hologres.hg_table_properties view instead of in the PostgreSQL catalog.

Connecting to a Hologres Instance

A Hologres instance is reached through an endpoint the console publishes, and there is no server configuration file to edit. Which endpoint you take decides whether the instance answers at all.

1. Copy the JDBC URL from the Hologres console. You will find it in the instance's Configurations page, which lists one endpoint for access from inside the VPC and one for access over the internet.
2. Take the endpoint that matches where DbSchema runs. The VPC endpoint resolves only from inside the same virtual private cloud. Running DbSchema on your own machine, you need the public endpoint, which the console creates on request rather than by default.
3. Allow your address in the instance's whitelist. An address outside the whitelist is refused before authentication, so a wrong entry here looks like a network timeout rather than a login failure. The whitelist takes your public IP or its CIDR block.
4. Sign in with an account Hologres knows. An AccessKey pair authenticates as the Alibaba Cloud account itself: the AccessKey ID is the user and the AccessKey Secret is the password. A RAM user needs the Hologres permissions granted in the console first, and its database privileges are granted in Hologres with the usual GRANT statements.
5. Choose the database, not the instance. Every instance starts with a postgres database that holds no user tables. Point the database field at the one you created, or connect to postgres first and use the Connection Dialog to list the others.
6. Connect from DbSchema. In the Connection Dialog choose Remote computer or custom port, fill in the server host and the port, then press Test Connection to check that the server answers before you connect.

Where the instance is deliberately kept off the internet, the Use SSL preset and an SSH tunnel through a host inside the VPC are the two ways in. Both are set in the Connection Dialog.

DbSchema and Hologres

DbSchema reads the Hologres physical design and shows it on the table, not only in the generated SQL: the distribution key, the clustering key and the event time column each appear as a key of their own, with their columns marked in the diagram, while the storage orientation, the table group and the time to live are kept as the table's options. Generating the schema writes them back into one WITH clause, so a model built in the designer creates tables that are laid out the way Hologres expects.