CODEWITHSUNDEEP
hyperledger-fabricblockchain
c fisher
c fisher

Reputation: 33

Can old block data be deleted from a blockchain?

Just a general question, if I'm building a blockchain for a business I want to store 3 years of transactions but anything older than that I won't need and don't want actively in the working database. Is there a way to backup and purge a blockchain or delete items older than some time frame? I'm more interested in the event logic than the forever memory aspect.

Upvotes: 2

Views: 2435

Answers (4)

Aberli
Aberli

Reputation: 1

it is almost impossible, if you want to change upcoming chains a 51% attack might be possible.

but if you want to change a block in the past it is almost impossible this could be destructive an entire blockchain network

Upvotes: 0

kajuken
kajuken

Reputation: 307

There are 2 concepts which help you achieve your goals.

The one thing is already mentioned. It is about Private Data. Private data gives you the possibility to 'label' data with a time to live. Then only the private data hashes are stored on the chain (to be able to verify this transaction) but the data itself is stored in so called SideDBs and gets fully pruned (except the hashes on the chain of course). This is kind of the basis for using Fabric without workarounds and achieving GDPR.

The other thing, which was not mentioned yet and kind of is very helpful to this question

Is there a way to backup and purge a blockchain or delete items older than some time frame?

Every peer only stores the 'current state' of the ledger in his StateDB. The current state could be described as the data which is labeled 'active' and probably soon to be used again. You can think of the StateDB being like a Cache. Every Data is comes into this Cache by creating or updating a new key (invoking). To remove a key from the Cache you can use 'DelState'. So it is labeled 'deleted' and not in the Cache anymore. BUT it is still on the ledger! and you can retrieve the history and data to that key.

Conclusion: For 'real' deleting of data you have to use the concept of Private Data and for managing data in your StateDB (think of the 'Cache' analogy) you can simply use built in functions.

Upvotes: 1

Hnampk
Hnampk

Reputation: 517

If you just want to purge the data after a while, Fabric Private Data has an option which could satisfy your desire.

blockToLive Represents how long the data should live on the private database in terms of blocks. The data will live for this specified number of blocks on the private database and after that it will get purged, making this data obsolete from the network so that it cannot be queried from chaincode, and cannot be made available to requesting peers

You can read more here.

Personally, I don't think there is a way to remove a block from the chain. It might destroy the Immutable property of blockchain.

Upvotes: 1

guoger
guoger

Reputation: 301

I'm not aware of any blockchain technology capable of this yet, but Hyperledger Fabric in particular is planning to support data archiving (checkpointing). Simply put, participants need to agree on a block height, so that older blocks can be discarded. This new block then becomes the source of trust, similar to original genesis block. Also, snapshot needs to be taken and consented, which captures current state.

From serviceability point of view, it's slightly more complicated, i.e. you may have nodes that are down while snapshotting, etc.

Upvotes: 2

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