Postgres-XC

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Now Moved

Postgres-XC Wiki page is now at new location. Please visit there for the latest information.

Project Overview

Postgres-XC (eXtensible Cluster) is a multi-master write-scalable PostgreSQL cluster based on shared-nothing architecture, developed by Postgres-XC Development Group. Introductory information can be found here (pdf&odp).

Features of PG-XC include:

  1. Write‐scalable PostgreSQL cluster
    • More than 3× scalability performance speedup with five servers, compared with pure PostgreSQL (DBT‐1). Result as of 1.0 release. Ways to improve more scalability are known.
  2. Synchronous multi‐master configuration
    • Any update to any master is visible from other masters immediately.
  3. Table location transparent
    • Can continue to use the same applications.
    • No change in transaction handling.
  4. Based upon PostgreSQL
  5. Same API to Apps as PostgreSQL

Project Status

Now under development.

  • Project license same as PostgreSQL, meaining PostgreSQL license (like BSD).

Project Property

This is Postgres-XC property according to the guideline as suggested here.

Overview

Please take a look at the top of this page.

Status

Version 1.2.1 released.

Status Detail

Infrastructure for the scalability and transaction management has already been done. Now the team is working to extend the coverage of statements, as well as HA feature. Latest version is v1.2.1.

Details of the roadmap can be found in the project home page.

Contacts

Core developers: Koichi Suzuki, Michael Paquier, Amit Khandekar, Ashutosh Bapat, Abbas Butt

Preferred method of contact: postgres-xc-general at lists.sourceforge.net or postgres-xc-developers at lists.sourceforge.net.

URL

We have Development Page and Project Home.

PGCon2011 Cluster Summit page is here

PGCon2011 Developer Meeting page is here

General Information

Scalability Evaluated with ten servers. Potentially twenty to thirty servers.
Read scaling Yes
Write scaling Yes
Triggers/procedures Procedure: Yes Trigger not yet
Parallel query Now some of the queries can be executed in parallel in multiple data nodes.
Failover/High Availability Yes Core features are available. External tools can be used for failover
Online provisioning No
PostgreSQL upgrades No All the nodes should be upgraded at the same time.
Detached node/WAN No Postgres-XC depends upon high speed communication.
PostgreSQL core modifications required Yes
Programming languages C, flex, bison, bash, perl (same as Postgres)
Licensing BSD, PostgreSQL license
Complete clustering solution Yes High-availability feature is already available, will be strengthened with next releases
PostgreSQL versions 9.3-based Planning to move to 9.4 once 9.4 stable branch is out

Model Summary

Synchronous multi-master.

Model description

Extracting transaction management into single server to provide transaction ID and snapshot, as well as other global values. Thus Postgres-XC provides consistent database view to any transactions running on any master.

Each table can be partitioned or replicated, as specified in CREATE TABLE statement. Distribution can be also done on a portion of nodes if wanted.

Use-case

Transactional use case.

  • Large scale transactional application,
  • Integration of multiple database applications.
  • Dynamic load balancing in cloud environment, assigning computing resource dynamically depending upon prospect load.

Drawbacks

General PostgreSQL clauses are supported. There are more challenges related to clustering though:

  • Tuple relocation. When the value of distribution column is updated, we have to relocate the tuple to appropriate one.
  • Global Deadlock detection. As discussed in cluster-hackers mailing list, there's no experience how long it will take to detect it and if it is reasonable compared with simple timeout mechanism.
  • Global constraint. Can we enforce unique or other constraint exclusion globally in multiple data nodes?

Support

Postgres-XC Development Group

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