用于行版本控制的RDBMS主键设计

Question

I want to design primary key for my table with row versioning. My table contains 2 main fields : ID and Timestamp, and bunch of other fields. For a unique "ID" , I want to store previous versions of a record. Hence I am creating primary key for the table to be combination of ID and timestamp fields. Hence to see all the versions of a particular ID, I can give,

Select * from table_name where ID=<ID_value>

To return the most recent version of a ID, I can use

Select * from table_name where ID=<ID_value> ORDER BY timestamp desc

and get the first element. My question here is, will this query be efficient and run in O(1) instead of scanning the entire table to get all entries matching same ID considering ID field was a part of primary key fields? Ideally to get a result in O(1), I should have provided the entire primary key. If it does need to do entire table scan, then how else can I design my primary key so that I get this request done in O(1)?

Thanks, Sriram

Answer 1

The canonical reference on this subject is Effective Timestamping in Databases : https://www.cs.arizona.edu/~rts/pubs/VLDBJ99.pdf

I usually design with a subset of this paper's recommendations, using a table containing a primary key only, with another referencing table that has that key as well change_user, valid_from and valid_until colums with appropriate defaults. This makes referential integrity easy, as well as future value insertion and history retention. Index as appropriate, and consider check constraints or triggers to prevent overlaps and gaps if you expose these fields to the application for direct modification. These have an obvious performance overhead.

We then make a "current values view" which is exposed to developers, and is also insertable via an "instead of" trigger.

Answer 2

It's far easier and better to use the History Table pattern for this.

create table foo (
  foo_id int primary key,
  name text
);

create table foo_history (
  foo_id int,
  version int,
  name text,
  operation char(1) check ( operation in ('u','d') ),
  modified_at timestamp,
  modified_by text
  primary key (foo_id, version)
);

Create a trigger to copy a foo row to foo_history on update or delete.

https://wiki.postgresql.org/wiki/Audit_trigger_91plus for a full example with postgres