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PolarDB for PostgreSQL (PolarDB for short) is an open-source database system based on PostgreSQL. It extends PostgreSQL to become a share-nothing distributed database, which supports global data consistency and ACID across database nodes, distributed SQL processing, and data redundancy and high availability through Paxos based replication. PolarDB is designed to add values and new features to PostgreSQL in dimensions of high performance, scalability, high availability, and elasticity. At the same time, PolarDB remains SQL compatibility to standalone PostgreSQL with the best effort.
PolarDB will evolve and offer its functions and features in two major parts: an extension and a patch to PostgreSQL. The extension part includes components implemented outside the PostgreSQL kernel, such as distributed transaction management, global or distributed time service, distributed SQL processing, additional metadata, internal functions, and tools to manage database clusters and conduct fault tolerance or recovery. Having most of its functions in a PostgreSQL extension, PolarDB targets easy upgrading, easy migration, and fast adoption. The patch part includes the changes necessary to the kernel, such as distributed MVCC for different isolation levels. We expect functions and codes in the patch part is limited. As a result, PolarDB can be easily upgraded with newer PostgreSQL versions and maintained full compatibility with PostgreSQL.
Three approaches are offered to quickly try out PolarDB: Alibaba Cloud service, deployment using Docker images, and deployment from source codes.
TBD
This section describes how to create a PolarDB-for-Postgresql image, and how to use the image for a quick start.
docker build -t polardb-for-postgresql -f ./docker/Dockerfile .
docker run --name polardb -p 10001:10001 -d polardb-for-postgresql:latest
psql -d postgres -U postgres -h localhost -p 10001
docker exec -it polardb /bin/bash
download source code from https://github.com/alibaba/PolarDB-for-PostgreSQL
install dependent packages (use Centos as an example)
sudo yum install bison flex libzstd-devel libzstd zstd cmake openssl-devel protobuf-devel readline-devel libxml2-devel libxslt-devel zlib-devel bzip2-devel lz4-devel snappy-devel python-devel
Call ssh-copy-id installs an authorized key. Its purpose is help pgxc_ctl to provision access without requiring a password for each login.
ssh-copy-id username@IP
vi ~/.bashrc
export PATH="$HOME/polardb/polardbhome/bin:$PATH"
export LD_LIBRARY_PATH="$HOME/polardb/polardbhome/lib:$LD_LIBRARY_PATH"
source ~/.bashrc
This script uses default configuration to compile PolarDB, to deploy binary, and to start a cluster of three nodes, including a leader and two followers. before call this script, please check "environment variables, dependent packages, authorized key" at "Previous Preparation" first.
./onekey.sh all
ps -ef|grep polardb
psql -p 10001 -d postgres -c "select * from pg_stat_replication;"
psql -p 10001 -d postgres -c "select * from polar_dma_cluster_status;"
We extend a tool named pgxc_ctl from PG-XC/PG-XL open-source project to support cluster management, such as configuration generation, configuration modification, cluster initialization, starting/stopping nodes, and switchover. Its detail usage can be found deployment.
You can just call build script to build. If you get errors, please reference deployment for detail reasons.
./build.sh
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf prepare standalone
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf deploy all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf clean all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf init all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf monitor all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf deploy cm
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf start all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf stop all
datanode_1 is node name configured in polardb_paxos.conf.
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf failover datanode datanode_1
check cluster status and start failed node.
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf healthcheck all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf kill all
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf log var datanodeNames
pgxc_ctl -c $HOME/polardb/polardb_paxos.conf show configuration all
ps -ef | grep postgres
psql -p 10001 -d postgres -c "create table t1(a int primary key, b int);"
createdb test -p 10001
psql -p 10001 -d test -c "select version();"
reference deployment for detail instructions.
Regress and other test details can be found here. Some benchmarking example is here.
PolarDB uses a share-nothing architecture. Each node stores data and also executes queries, and they coordinate with each other through message passing. The architecture allows the database to be scaled by adding more nodes to the cluster.
PolarDB slices a table into shards by hashing its primary key. The number of shards is configurable. Shards are stored in PolarDB nodes. When a query accesses shards in many nodes, a distributed transaction and a transaction coordinator are used to maintain ACID across nodes.
Each shard is replicated to three nodes with each replica stored on a different node. In order to save costs, we can deploy two of the replicas to store complete data. The third replica only stores a write-ahead log (WAL), which participates in the election but cannot be chosen as the leader.
See architecture design for more information
PolarDB is built on open-source projects and extends open-source PostgreSQL. Your contribution is welcome and appreciated. Please refer contributing for how to start coding and submit a PR.
PolarDB code is released under the Apache Version 2.0 License and the Licenses with PostgreSQL code.
The relevant licenses can be found in the comments at the top of each file.
Reference License and NOTICE for details.
Some codes and design ideas were from other open-source projects, such as PG-XC/XL(pgxc_ctl), TBase (part of timestamp-based vacuum and MVCC), and Citus (pg_cron). Thanks for their contributions.
PolarDB for PostgreSQL at Slack https://app.slack.com/client/T023NM10KGE/C023VEMKS02
PolarDB Technial Promotion Group at DingDing
Copyright © Alibaba Group, Inc.
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