ScalarDB FDW is a PostgreSQL extension that implements a foreign data wrapper (FDW) for ScalarDB.
ScalarDB FDW uses the Java Native Interface to directly utilize ScalarDB as a library inside the FDW and read data from external databases via scan operations for ScalarDB.
You must have the following prerequisites set up in your environment.
You must install a version of the Java Development Kit (JDK) that is compatible with ScalarDB. In addition, you must set the
JAVA_HOME environment variable, which points to your JDK installation directory.
Note that since these extensions use the Java Native Interface (JNI) internally, you must include the dynamic library of the Java virtual machine (JVM), such as
libjvm.so, in the library search path.
This extension supports PostgreSQL 13 or later. For details on how to install PostgreSQL, see the official documentation at Server Administration.
Build and installation
You can build and install this extension by running the following command.
Common build errors
This section describes some common build errors that you might encounter.
ld: library not found for -ljvm
Normally, the build script finds the path for
libjvm.so and properly sets it as a library search path. However, if you encounter the error
ld: library not found for -ljvm, please copy the
libjvm.so file to the default library search path. For example:
ln -s /<PATH_TO_YOUR_LIBJVM_FILE>/libjvm.so /usr/lib64/libjvm.so
This section provides a usage example and available options for FDW for ScalarDB.
The following example shows you how to install and create the necessary components, and then run a query by using the FDW extension.
1. Install the extension
For details on how to install the extension, see the Build and installation section.
2. Create an extension
To create an extension, run the following command:
CREATE EXTENSION scalardb_fdw;
3. Create a foreign server
To create a foreign server, run the following command:
CREATE SERVER scalardb FOREIGN DATA WRAPPER scalardb_fdw OPTIONS (
4. Create user mapping
To create user mapping, run the following command:
CREATE USER MAPPING FOR PUBLIC SERVER scalardb;
5. Create a foreign table
To create a foreign table, run the following command:
CREATE FOREIGN TABLE sample_table (
float_col double precision,
double_col double precision,
) SERVER scalardb OPTIONS (
6. Run a query
To run a query, run the following command:
select * from sample_table;
You can set the following options for ScalarDB FDW objects.
You can set the following options on a ScalarDB foreign server object:
|The path to the ScalarDB config file.
|The maximum heap size of JVM. The format is the same as
CREATE USER MAPPING
Currently, no options exist for
CREATE USER MAPPING.
CREATE FOREIGN SERVER
The following options can be set on a ScalarDB foreign table object:
|The name of the namespace of the table in the ScalarDB instance.
|The name of the table in the ScalarDB instance.
This section describes how to test FDW for ScalarDB.
Set up a ScalarDB instance for testing
Before testing FDW for ScalarDB, you must have a running ScalarDB instance that contains test data. You can set up the instance and load the test data by running the following commands:
If you want to reset the instances, you can run the following command, then the above setup command again.
Run regression tests
You can run regression tests by running the following command after you have installed the FDW extension.
- This extension aims to enable analytical query processing on ScalarDB-managed databases. Therefore, this extension only supports reading data from ScalarDB.