Correcting Transfers

Transfers in TigerBeetle are immutable, so once they are created they cannot be modified or deleted.

Immutability is useful for creating an auditable log of all of the business events, but it does raise the question of what to do when a transfer was made in error or some detail such as the amount was incorrect.

Always Add More Transfers

Correcting transfers or entries in TigerBeetle are handled with more transfers to reverse or adjust the effects of the previous transfer(s).

This is important because adding transfers as opposed to deleting or modifying incorrect ones adds more information to the history. The log of events includes the original error, when it took place, as well as any attempts to correct the record and when they took place. A correcting entry might even be wrong, in which case it itself can be corrected with yet another transfer. All of these events form a timeline of the particular business event, which is stored permanently.

Another way to put this is that TigerBeetle is the lowest layer of the accounting stack and represents the finest-resolution data that is stored. At a higher-level reporting layer, you can "downsample" the data to show only the corrected transfer event. However, it would not be possible to go back if the original record were modified or deleted.

Two specific recommendations for correcting transfers are:

1. You may want to have a Transfer.code that indicates a given transfer is a correction, or you may want multiple codes where each one represents a different reason why the correction has taken place.
2. If you use the Transfer.user_data_128 to store an ID that links multiple transfers within TigerBeetle or points to a record in an external database, you may want to use the same user_data_128 field on the correction transfer(s), even if they happen at a later point.

Example

Let's say you had a couple of transfers, from account A to accounts Y and Z:

Ledger	Debit Account	Credit Account	Amount	code	user_data_128	flags.linked
USD	A	X	10000	600	123456	true
USD	A	Y	50	9000	123456	false

Now, let's say we realized the amount was wrong and we need to adjust both of the amounts by 10%. We would submit two additional transfers going in the opposite direction:

Ledger	Debit Account	Credit Account	Amount	code	user_data_128	flags.linked
USD	X	A	1000	10000	123456	true
USD	Y	A	5	10000	123456	false

Note that the codes used here don't have any actual meaning, but you would want to enumerate your business events and map each to a numeric code value, including the initial reasons for transfers and the reasons they might be corrected.