Sawtooth Transaction headers have a dependencies field and which is an array of transaction headers that need to be added to the ledger before this transaction is processed.
Where are transactions with unmet dependencies stored? Are they stored in the node that first received them or stored in every node in the network?
The Validator stores incoming transactions in the pending queue. The Validator consumes the transaction from the pending queue for execution. Execution of the Transaction is done either when a Block is created or Block is validated. Addition of a Transaction to the Block is triggered by the consensus engine action.
A Transaction is broadcasted to other Validators part of that network as and when they arrive. It is removed from the pending queue if either the Transaction is evaluated, either failed or successful. If a Transaction is successful it should be either during the Block creation or the Block validation. If the created Block fails to be committed because of the consensus process, these Transactions are added back to the pending queue. There was nothing wrong with the Transaction as such, it just happened to be not part of the Block that is committed. A Transaction in other terms completely removed from the pending queue in successful case when it is committed to a Block.
When I say Transaction is pended at the Validator, of-course what is received is a Batch. Dependency check is done by the Validator when it considers a Transaction be added to the Block.
Hope this answers the question. Please add specific question if you're facing any issue or want to know in detail.
Related
Corda doc says "If a transaction is not checked for validity (non-validating notary), it creates the risk of “denial of state” attacks, where a node knowingly builds an invalid transaction consuming some set of existing states and sends it to the notary cluster, causing the states to be marked as consumed"
In this case, does "invaid transaction" include simply mistaking transaction such as passing too high value input by type mistakes and invalidated by flow step?
How denial of state attacks could be caused.
"Denial of State" could be caused if a rogue node builds a transaction and consumes a state which is shared between multiple parties. This is a trade-off of using non-validating notary as it doesn't validate the transaction against the contract code. The other parties would not be able to use the state anymore as it would already be consumed.
I am working on building a page to check whether is there any confirmed transaction for all the address in my wallet that i created.
$webHook->setUrl("https://requestb.in/r0dspfr0");
$webHook->setEvent('confirmed-tx');
$webHook->setToken('my_token');
$webHook->setWalletName('andy');
The problem here is i only want it to callback to that url whenever a transction had six confirmations.
I had tried to set the event to tx-confirmation or others, it cant work as what i want, it will always callback when there is only one confirmation, after that it stop.
Are u using the Java sdk?
You can try "tx-confirmation" and only process the transactions with 6 confirmations
confirmed-tx Triggered for every new transaction making it into a new block; in other words, for every first transaction confirmation. This is equivalent to listening to the new-block event and fetching each transaction in the new Block. The payload is a confirmed TX.
tx-confirmation Simplifies listening to confirmations on all transactions for a given address up to a provided threshold. Sends first the unconfirmed transaction and then the transaction for each confirmation. Use the confirmations property within the Event to manually specify the number of confirmations desired (maximum 10, defaults to 6). The payload is a TX.
I'm going through the documentation on Hyperledger Fabric, and there's a portion in the introduction that writes:
"Hyperledger Fabric assigns network roles by node type. To provide concurrency and parallelism to the network, transaction execution is separated from transaction ordering and commitment. Executing transactions prior to ordering them enables each peer node to process multiple transactions simultaneously."
Maybe this is some fundamental misunderstanding on my part about the structure of the network and the different functions and mechanics of nodes, but how can one execute a transaction prior to ordering one?
Within a Hyperledger Fabric network, transactions start out with client applications sending transaction proposals, or, in other words, proposing a transaction to endorsing peers.
Each endorsing peer simulates the proposed transaction, without updating the ledger. The endorsing peers will capture the set of Read and Written data, called RW Sets.
These RW sets are then signed by the endorsing peer, and returned to the client application to be used in future steps of the transaction flow. Endorsing peers must hold smart contracts in order to simulate the transaction proposals.
The application then submits the endorsed transaction and the RW sets to the ordering service. Ordering happens across the network, in parallel with endorsed transactions and RW sets submitted by other applications.
The ordering service takes the endorsed transactions and RW sets, orders this information into a block, and delivers the block to all committing peers.
The committing peer validates the transaction by checking to make sure that the RW sets still match the current world state.
Committing peers are responsible for adding blocks of transactions to the shared ledger and updating the world state.
Here, you have the roles that there are in Hyperledger Fabric:
Endorser Peers: they receive a transaction. Then, they execute the transaction against the Smart Contrat and they sign the result. They send the transaction signed to the peer that has sent it.
Committer Peers: the Peers get the Blocks (with the validates transactions) and commit them to its ledger.
Orderes: nodes that sort the transactions and generate the blocks.
I take this info from an answer that I write for a question.
Let's say I have two chaincode in Hyperledger Fabric, ChaincodeA and ChaincodeB.
Some events in ChaincodeA will have to change state in ChaincodeB, for example, change its balance. If invokeChaincode() used in ChaincodeA to invoke some logic in ChaincodeB, which calls putState() to change ChaincodeB's state, any race condition could happen when getting consensus? What's the best practices on handling this?
While invoking a chaincode you do not change the state you only simulate transaction execution based on the current state. Only once transaction placed into the block by ordering service and reaches the peer where it has to pass VSCC and MVCC checks it gonna be eventually committed. MVCC will take care of possible race condition. Transaction execution works as following:
Client sends transaction proposal to the peer
Peer simulates transaction sign the results and put them into signed transaction proposal
Client has to repeat step #2 based on expected endorsement policies
Once client collected enough endorsements he send them to the ordering service
Ordering service cuts the block and order all transaction
Block delivered to the peers
Peer validates and eventually commits the block
As I understated two chaincode deployed on two different channels. chaincodeA want to call method of chaincodeB. As per specification its possible but only for read operation.
https://godoc.org/github.com/hyperledger/fabric/core/chaincode/shim#ChaincodeStub.InvokeChaincode
can you please share code how you are calling another chaincodeB from chaincodeA?
Given that I am a bit confused with CQRS I would like to understand it further in the following scenario.
I have an Actor that charge Users' credit card. To do so it contact a bank external service that does the operation, get a confirmation result. I would like to know how can I apply this with CQRS.
The information that needs to be written here is that a specific user has been charge a certain amount. So the event generated is Charged (UserID, Card, Amount). Something like that.
The problem is that all the examples I have seen especially with AKKA, would only generate the event after a Command is validated, such that it is persisted in a journal, and used to update the state of the actor. The Journal could then be red on the other side, such that to create a Reading view here.
Also usually, in those examples, the update state function has a logic that somewhat execute the command, because the command correspond straightforwardly to a state update at the end of the day. This is the typical BasketShoping example: CreateOrder, AddLineItem. All Of this Command, are directly translated in Event, that correspond to a specific code of the Update state function.
However in this example, one needs to actually contact an external service, charge the user and then generate an event. Contacting the external service can't be done in the update state, or after reading the journal. It would not make sense.
How is that done, and where, and when exactly, in the spirit of CQRS?
I can think of 2 ways of doing this.
First is a simple way. The command is DoCharge(UserId, Card, Amount). Upon reception of this command, you call the external payment service. If this has been successfully completed, you generate an event, Charged(UserId, Card, Amount, TransactionId) and store it in the journal.
Now, of course, it's not completely safe way, because your Actor can crash after it has sent the request to payment service, but before it has received and persisted the confirmation of the successful completion. Then you risk of charging the user twice. To overcome this risk, you have to make your payment operation idempotent. Here's how to do it. This example is based on the classic "RESTify Day trader" article. I'll summarize it here.
You need to split the payment operation in 2 phases. In first one, payment service creates a transaction token. It just identifies the transaction, and no financial operations are performed yet. Upon the creation, the identifier is received by your service and persisted in the journal.
In next phase you perform a payment associated with the identifier from phase one. If your actor now fails in the middle, while operation is performed successfully on the payment service side, the transaction token will already be marked as processed by the payment service, and it won't let you charge the customer twice. Now, if you restart the failed Actor, and it tries to run the payment associated with the existing transaction token, the payment service should return result like "Already executed" or such. Of course, at the end you also persist the result of the operation in the journal.