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Postgres-XL is a massively parallel database built on top of PostgreSQL 9.5 and highly compatible with PostgreSQL 9.5. It differs in that it supports both business intelligence workloads and high-capacity transaction write and read workloads.

Postgres-XL is an open source PG cluster software. XL stands for eXtensible Lattice, which means extensible PG "grid", hereinafter referred to as PGXL. Officials say it is suitable not only for OLTP applications with high write operation pressure, but also for big data applications with read operation as the main operation. Its predecessor is Postgres-XC (PGXC for short). PGXC adds clustering function on the basis of PG, which is mainly suitable for OLTP applications; PGXL is an upgrade product based on PGXC, adding some features suitable for OLAP applications, such as Massively Parallel Processing (MPP) features. Generally speaking, the code of PGXL contains PG code, and installing a PG cluster using PGXL does not require a separate installation of PG. One of the problems caused by this is that it is impossible to choose any version of PG at will. Fortunately, it is more timely for PGXL to follow up with PG. The latest version, Postgres-XL 9.5R1.3, is based on PG 9.5.

Introduction to components:

Global Transaction Monitor (GTM)

The global transaction manager ensures cluster-wide transaction consistency. GTM is responsible for issuing transactional ID and snapshots as part of its multiversion concurrency control.

The cluster optionally configures a backup GTM to improve availability. In addition, proxy GTM can be configured between coordinators, which can be used to improve scalability and reduce GTM traffic.

GTM Standby

The standby node of GTM. In pgxc,pgxl, GTM controls all global transaction allocation. If there is a problem, it will cause the whole cluster to be unavailable. In order to increase availability, add the standby node. When there is a problem with GTM, GTM Standby can be upgraded to GTM to ensure that the cluster works properly.

GTM-Proxy

GTM needs to communicate with all Coordinators, and to reduce stress, you can deploy a GTM-Proxy on each Coordinator machine.

Coordinator

The coordinator manages user sessions and interacts with GTM and data nodes. The coordinator parses and plans the query and sends the next serialized global plan to each component in the statement.

To save machines, this service is usually deployed with data nodes.

Data Node

A data node is the place where data is actually stored. The distribution of data can be configured by DBA. To improve availability, you can configure the hot backup of the data node for failover preparation.

Summary: gtm is responsible for ACID to ensure the consistency of global transactions in distributed databases. Thanks to this, even if the data nodes are distributed, when you add, delete, change and query transactions in the master node, it is as simple as operating only one database. Coordinator is scheduled and sends operation instructions to each data node. Datanodes is a data node that stores data distributed.

Family history:

Postgres-XL and Postgresql-XC

In 1994, Postgre95 was released as open source.

In 1996, PostgreSQL inherited Postgre95, the release.

In 2010, Postgres-XC was released.

In 2012, the former core developer of PGXC founded StormDB with a number of improvements, including performance improvements to MPP parallelization and multi-tenant security.

In 2013, TransLattice acquired StormDB.

In 2014, the project was open source and named Postgres-XL.

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