split-exec

split-exec: A sleek and efficient database Online DML change tool with zero online impact, perceptible progress, and controllable latency.

current status: developing, Maybe product first available release at April 15 2024

Why?

When using a database (such as MySQL or PostgreSQL), we often need to perform DML operations that can affect a large amount of rows. This type of SQL, referred to as "Big-SQL" in the following text.

For example, when data expires, we may want to:

• Mark old data as deleted. This can be done using a SQL update statement like:

  update online_task status='deleted' where create_time<'2023-02-01'

• Delete old data to reclaim space. This can be achieved with an SQL delete statement like:

  delete from online_task where create_time<'2023-02-01'

• Migrate data from the live table to an archive table. This can be done using an SQL insert statement like:

  insert into archive_task select * from online_task where create_time<'2023-02-01

However, executing Big-SQL directly on table may cause many troubles, such as:

• Coarse-grained locks held by Big-SQL during executing impact live queries.
• Big-SQL involving large amounts of data cause extensive CPU and IO operations.
• Replaying Big-SQL also costs too long time, during replaying replicas have data latency.

Risk Summary: overhead connection limit, connection denied accumulation of slow queries data latency.

Otherwise, executing Big-SQL directly like a black-box, we are unable to estimate how much more time is required.

How?

To address this issue, we aim to split a large SQL query into smaller sub-queries based on the primary key or unique key. Additionally, while executing these sub-queries, we monitor the data latency between the master and replicas.

The sample design of flow is like:

TODO: add

Usage

TODO