PostgreSQL 15 preview - Skip empty transactions for logical replication

作者

digoal

日期

2022-03-31

标签

PostgreSQL , logical replication , 空事务

当事务中没有包含发布端的数据、或者包含的数据全部都被定义的过滤器过滤掉了, 这个事务的信息不应该发送给订阅端, 否则是浪费网络带宽和CPU.

PostgreSQL 15 支持跳过此类的“空事务” , 并且在synchronous 复制模式下, 使用定时的心跳包代替空事务.

https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=d5a9d86d8ffcadc52ff3729cd00fbd83bc38643c

Skip empty transactions for logical replication.  
author  Amit Kapila <akapila@postgresql.org>      
Wed, 30 Mar 2022 02:11:05 +0000 (07:41 +0530)  
committer   Amit Kapila <akapila@postgresql.org>      
Wed, 30 Mar 2022 02:11:05 +0000 (07:41 +0530)  
commit  d5a9d86d8ffcadc52ff3729cd00fbd83bc38643c  
tree    2b5497206cf558509284df8817bd350e4d27dbb1    tree  
parent  ad4f2c47de440cdd5d58cf9ffea09afa0da04d6c    commit | diff  
Skip empty transactions for logical replication.  
The current logical replication behavior is to send every transaction to  
subscriber even if the transaction is empty. This can happen because  
transaction doesn't contain changes from the selected publications or all  
the changes got filtered. It is a waste of CPU cycles and network  
bandwidth to build/transmit these empty transactions.  
This patch addresses the above problem by postponing the BEGIN message  
until the first change is sent. While processing a COMMIT message, if  
there was no other change for that transaction, do not send the COMMIT  
message. This allows us to skip sending BEGIN/COMMIT messages for empty  
transactions.  
When skipping empty transactions in synchronous replication mode, we send  
a keepalive message to avoid delaying such transactions.  
Author: Ajin Cherian, Hou Zhijie, Euler Taveira  
Reviewed-by: Peter Smith, Takamichi Osumi, Shi Yu, Masahiko Sawada, Greg Nancarrow, Vignesh C, Amit Kapila  
Discussion: https://postgr.es/m/CAMkU=1yohp9-dv48FLoSPrMqYEyyS5ZWkaZGD41RJr10xiNo_Q@mail.gmail.com  

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