Johan Sölve@macsolve

http://re.solve.se

Relational databases

• Two dimensional

• Rows and columns

• Only know about NOW

• Has no concept of ”history”

What if we can add a

third dimension?

What if we can add the notion of

TIME

Data Versioning

Data Versioning

• ”Time Machine” for data

• Snapshot of any point in time

• Immediately and continously available

• No rollback or restore of database

• Demo:

http://johan.solve.se/dataversioning/

Data Versioning

• Consistent across tables

• Solution for MySQL

• Uses VIEW to access data

• Data access it transparent to the application

• Unique for each database session/visitor

Views

• Views are like search macros

• They are created as a saved SELECT statement

• Performs good if indexed properly

Data Versioning

• Each table is replaced by a ”data” table that maintains every version of each row/record

• Common ”version” table

• Points at current row in data table

• Keeps meta data about changes

• Each table is completed by a VIEW to

Never Change

• Most important:

• Never update or delete a row in the data table

• All changes add a new row in the data table

Time

Row 1Row 2Row 3Row 4Row 5

Table

Time

Row 1Row 2Row 3Row 4Row 5

Table

Table 2

Row 1Row 2Row 3Row 4

Database operations– CRUD

• SELECT from a view - just as usual

• INSERT creates a row in data table and verison table

• UPDATE updates a timestamp in the version table and creates a row in the data table and version table

• DELETE updates a timestamp in the version table

Database operations– CRUD

• SELECT – no change

• INSERT, UPDATE, DELETE handles specially

• Triggers and Stored procedures

• Or in the application’s database abstraction layer

INSERT

INSERT INTO version (guid, changedby_start) VALUES ("gweyufghkj", "JS");

INSERT INTO people_data (id_version, firstname, lastname) VALUES(LAST_INSERT_ID(), "Nisse", "Hult");

UPDATE

UPDATE version SET changedby_end="JS", dt_end=NOW() WHERE guid="gweyufghkj" AND dt_end="3000-01-01 00:00:00";

INSERT INTO version (guid, changedby_start) VALUES ("gweyufghkj", "JS");

DELETE

UPDATE version SET changedby_end="JS", dt_end=NOW() WHERE guid="gweyufghkj" AND dt_end="3000-01-01 00:00:00";

SELECT

SELECT * FROM people;

View

CREATE VIEW people AS

SELECT people_data.*, version.guid

FROM people_data

JOIN version ON

people_data.id_version=version.id

WHERE dt_start <= history()

AND dt_end > history();

Go Back in Time

SET @history="2010-02-22 10:00:00";

SELECT * FROM people;

Only affects this database session

Uses

• Content Management

• Definitions for dynamic forms

• Data entry must match form definition at any point in time

Considerations• Carefully evaluate for each table if it’s

relevant to include it in data versioning

Example:

• Permission settings

• What if the table structure changes?

• Performance

• Consider using emulated

Implementation

• Modified knop_database

• Methods for:

-> addrecord

-> saverecord

-> deleterecord

Read more

• Description:

http://re.solve.se/database-versioning

• Demo:

http://johan.solve.se/dataversioning/

Johan Sölve