PGSpider is High-Performance SQL Cluster Engine for distributed big data. PGSpider can access a number of data sources using Foreign Data Wrapper(FDW) and retrieves the distributed data source vertically.
PGSpider source code is patch for PostgreSQL. You should apply this to PostgreSQL source code if you want to use PGSpider. Usage of PGSpider is the same as PostgreSQL. You can use any client applications such as libpq and psql.

• Multi-Tenant User can get records in multi tables by one SQL easily. If there are tables with similar schema in each data source, PGSpider can view them as a single virtual table: We call it as Multi-Tenant table.

• Parallel processing
  PGSpider executes queries and fetches results from child nodes in parallel.
  PGSpider expands Multi-Tenant table to child tables, creates new threads for each child table to access corresponding data source.

• Pushdown
  WHERE clause and aggregation functions are pushed down to child nodes. Pushdown to Multi-tenant tables occur error when AVG, STDDEV and VARIANCE are used. PGSPider improves this error, PGSpider can execute them.

The current version can work with PostgreSQL 11.6.

Download PostgreSQL source code.

https://www.postgresql.org/ftp/source/v11.6/postgresql-11.6.tar.gz

Decompress PostgreSQL source code.

tar xvf postgresql-11.6.tar.gz

Apply patch.

patch -p1 -d postgresql-11.6 < pgspider.patch

Build and install PGSpider and extensions.

cd postgresql-11.6
./configure
make
sudo make install
cd contrib/pgspider_core_fdw
make 
sudo make install
cd ../pgspider_fdw
make 
sudo make install

Default install directory is /usr/local/pgspider .

For example, we will create 2 different child nodes, SQLite and PostgreSQL. They are accessed by PGSpider as root node. Please install SQLite and PostgreSQL for child nodes.

After that, we install PostgreSQL FDW and SQLite FDW into PGSpider.

Install SQLite FDW

cd ../
git clone https://github.com/pgspider/sqlite_fdw.git
cd sqlite_fdw
make
sudo make install

Install PostgreSQL FDW

cd ../postgres_fdw
make 
sudo make install

PGSpider binary name is same as PostgreSQL. Default install directory is changed.

/usr/local/pgspider

Create database cluster and start server.

cd /usr/local/pgspider/bin
./initdb -D ~/pgspider_db
./pg_ctl -D ~/pgspider_db start

Connect to PGSpider.

./psql postgres

PGSpider(Parent node)

CREATE EXTENSION pgspider_core_fdw;

PostgreSQL,SQLite(Child node)

CREATE EXTENSION postgres_fdw;
CREATE EXTENSION sqlite_fdw;

PGSpider(Parent node)

CREATE SERVER parent FOREIGN DATA WRAPPER pgspider_core_fdw OPTIONS (host '127.0.0.1', port '5432');

PostgreSQL,SQLite (Child node)
In this example, child PostgreSQL node is localhost and port is 15432.
SQLite node's database is /tmp/temp.db.

CREATE SERVER postgres_svr FOREIGN DATA WRAPPER postgres_fdw OPTIONS(host '127.0.0.1', port '15432', dbname 'postgres');
CREATE SERVER sqlite_svr FOREIGN DATA WRAPPER sqlite_fdw OPTIONS(database '/tmp/temp.db');

PGSpider(Parent node)

Create user mapping for PGSpider. User and password are for current psql user.

CREATE USER MAPPING FOR CURRENT_USER SERVER parent OPTIONS(user 'user', password 'pass');

PostgreSQL(Child node)

CREATE USER MAPPING FOR CURRENT_USER SERVER postgres_svr OPTIONS(user 'user', password 'pass');

SQLite(Child node)
No need to create user mapping.

PGSpider(Parent node)
You need to declare a column named "__spd_url" on parent table. This column is node location in PGSpider. It allows you to know where the data is comming from node.
In this example, we define 't1' table to get data from PostgreSQL node and SQLite node.

CREATE FOREIGN TABLE t1(i int, t text, __spd_url text) SERVER parent;

When expanding Multi-Tenant table to data source tables, PGSpider searches child node tables by name having [Multi-Tenant table name]__[data source name]__0.

PostgreSQL,SQLite(Child node)

CREATE FOREIGN TABLE t1__postgres_svr__0(i int, t text) SERVER postgres_svr OPTIONS (table_name 't1');
CREATE FOREIGN TABLE t1__sqlite_svr__0(i int, t text) SERVER sqlite_svr OPTIONS (table 't1');

SELECT * FROM t1;

  i |  t  | __spd_url 
----+-----+----------------
  1 | aaa | /sqlite_svr/
  2 | bbb | /sqlite_svr/
 10 | a   | /postgres_svr/
 11 | b   | /postgres_svr/
(4 rows)

You can choose getting node with 'IN' clause after FROM items(Table name).

SELECT * FROM t1 IN ('/postgres_svr/');

  i | t | __spd_url 
----+---+----------------
 10 | a | /postgres_svr/
 11 | b | /postgres_svr/
(2 rows)

PGSpider can get data from child PGSpider, it means PGSpider can create tree structure.
For example, we will create a new PGSpider as root node which connects to PGSpider of previous example. The new root node is parent of previous PGSpider node.

Create new database cluster with initdb and change port number.
After that, start and connect to new root node.

PGSpider(new root node)
If child node is PGSpider, PGSpider use pgspider_fdw.

CREATE EXTENSION pgspider_core_fdw;
CREATE EXTENSION pgspider_fdw;

PGSpider(new root node)

CREATE SERVER new_root FOREIGN DATA WRAPPER pgspider_core_fdw OPTIONS (host '127.0.0.1', port '54321') ;

PGSpider(Parent node)

CREATE SERVER parent FOREIGN DATA WRAPPER pgspider_svr OPTIONS
(host '127.0.0.1', port '5432') ;

PGSpider(new root node)

CREATE USER MAPPING FOR CURRENT_USER SERVER new_root OPTIONS(user 'user', password 'pass');

PostgreSQL(Parent node)

CREATE USER MAPPING FOR CURRENT_USER SERVER parent OPTIONS(user 'user', password 'pass');

PGSpider(new root node)

CREATE FOREIGN TABLE t1(i int, t text, __spd_url text) SERVER new_root;

PGSpider(Parent node)

CREATE FOREIGN TABLE t1__parent__0(i int, t text, __spd_url text) SERVER parent;

SELECT * FROM t1;

  i |  t  |      __spd_url 
----+-----+-----------------------
  1 | aaa | /parent/sqlite_svr/
  2 | bbb | /parent/sqlite_svr/
 10 | a   | /parent/postgres_svr/
 11 | b   | /parent/postgres_svr/
(4 rows)

When a query to foreign tables fails, you can find why it fails by seeing a query executed in PGSpider with EXPLAIN (VERBOSE).

Opening issues and pull requests on GitHub are welcome.

Copyright and license information can be found in the file License .