CODEWITHSUNDEEP
database
SunnyIsaLearner
SunnyIsaLearner

Reputation: 780

What is a ledger in the context of database?

I have overheard discussion like "Should this be put into a ledger instead of an update?" I have some feeling that is has to do with record keeping, but I cannot fully understand what is a ledger. Searching both on stackoverflow and google runs into accounting related articles.

So my question is, what is a ledger when talking about database applications?

Upvotes: 2

Views: 217

Answers (1)

Catalin Oancea
Catalin Oancea

Reputation: 103

A ledger usually refers to a collection of states through which an entity passed. The difference between an update and storing the data in a ledger is that when using update you don't have a history of all the updates performed on a certain entity.

The most common example for ledgers is indeed a banking model. You can better see the difference in the example below:

With updates, every time a client withdraws or deposits money, you just update the amount of money that client owns:

user_id         | ammount
-----------------------------
26KRZT          | 45

Having a ledger, you can keep the entire history of the transactions (and compute the amount based on the client's transactions)

user_id         | operation         | ammount   
----------------------------------------------------
26KRZT          | DEPOSIT           | 25
26KRZT          | DEPOSIT           | 35
26KRZT          | WITHDRAW          | 15

Basically, a ledger stores data in the database as diffs (updates to the previous version of an entity) in order to be able to get a change history for a given entity.

Upvotes: 3

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