PostgresForeignDataWrapper

This PostgreSQL extension implements a Foreign Data Wrapper (FDW) for RocksDB. This repo has been listed in PostgreSQL wiki.

RocksDB is a high performance key-value store based on a log-structured merge-tree (LSM tree). RocksDB can efficiently use many CPU cores and fast storage. This is the first foreign data wrapper that connects a LSM-tree-based storage engine to PostgreSQL. Because RocksDB is an embeddable key-value store, you do not need to run another server to use this extension.

This extension can also be used for other systems that have RocksDB-like APIs, but please check the compatibility before you use this extension for other systems.

This extension is developed and maintained by the VidarDB team. Feel free to report bugs or issues via Github.

Building

We test this foreign data wrapper on Ubuntu Server 18.04 using PostgreSQL-11 together with RocksDB-6.2.4 (built with GCC-7.4.0).

Install PostgreSQL and the dev library which is required by extensions:

# add the repository
sudo tee /etc/apt/sources.list.d/pgdg.list << END
deb http://apt.postgresql.org/pub/repos/apt/ bionic-pgdg main
END

# get the signing key and import it
wget https://www.postgresql.org/media/keys/ACCC4CF8.asc
sudo apt-key add ACCC4CF8.asc

# fetch the metadata from the new repo
sudo apt-get update

# install postgresql and the dev library
sudo apt-get install postgresql-11
sudo apt-get install postgresql-server-dev-11

Install RocksDB from source code:

git clone -b v6.2.4 https://github.com/facebook/rocksdb.git

cd rocksdb

sudo DEBUG_LEVEL=0 make shared_lib install-shared

sudo sh -c "echo /usr/local/lib >> /etc/ld.so.conf"  

sudo ldconfig

Build this foreign data wrapper:

git clone git@github.com:postgrespro/lsm.git

cd lsm

make

sudo make install

Before using this foreign data wrapper, we need to add it to shared_preload_libraries in the postgresql.conf:
```
echo "shared_preload_libraries = 'lsm'" >> postgresql.conf
```
and restart PostgreSQL:
```
sudo service postgresql restart
```
When uninstall this extension, first issue the following commands, and then delete the data by locating PostgreSQL data folder via show data_directory; in PostgreSQL terminal.
```
cd PostgresForeignDataWrapper

sudo make uninstall
```

Limitations

The first attribute in the table definition must be the primary key.
Composite primary key is not supported for now.
ACID relies on the storage engine.
Data types of Postgres are not natively supported.

Usage

This extension does not have any parameter. After creating the extension and corresponding server, you can use RocksDB as a foreign storage engine for your PostgreSQL.

A simple example is as follows (you can run 'sudo -u postgres psql -U postgres' to connect the local postgresql server):

    CREATE DATABASE example;  
    \c example  

    CREATE EXTENSION lsm;  
    CREATE SERVER lsm_server FOREIGN DATA WRAPPER lsm_fdw;  

    CREATE FOREIGN TABLE student(id INTEGER, name TEXT) SERVER lsm_server;  

    INSERT INTO student VALUES(20757123, 'Rafferty');  
    SELECT * FROM student;  

    INSERT INTO student VALUES(20767234, 'Jones');  
    SELECT * FROM student;  

    DELETE FROM student WHERE name='Jones';  
    SELECT * FROM student;  

    UPDATE student SET name='Tom' WHERE id=20757123;  
    SELECT * FROM student;  

    DROP FOREIGN TABLE student;  

    DROP SERVER lsm_server;  
    DROP EXTENSION lsm_fdw;  
  
    \c postgres  
    DROP DATABASE example;

Testing

We have tested certain typical SQL statements and will add more test cases later. The test scripts are in the test/sql folder which are recommended to be placed in a non-root directory. The corresponding results can be found in the test/expected folder. You can run the tests in the following way:

    sudo service postgresql restart  

    cd PostgresForeignDataWrapper

    sudo -u postgres psql -U postgres -a -f test/sql/create.sql 

    sudo -u postgres psql -U postgres -d lsmtest -a -f test/sql/test.sql 

    sudo -u postgres psql -U postgres -d lsmtest -a -f test/sql/clear.sql

Debug

If you want to debug the source code, you may need to start PostgreSQL in the debug mode:

    sudo service postgresql stop  

    sudo -u postgres /usr/lib/postgresql/11/bin/postgres -d 0 -D /var/lib/postgresql/11/main -c config_file=/etc/postgresql/11/main/postgresql.conf

Docker

We can also run PostgreSQL with RocksDB in Docker container and you can refer to here.