Topic: Blockchain.info custom transaction (Read 963 times)

So i guess it's normal... Thanks a lot for your feedback!

Okay so I did a little bit of experimenting. 184QFyikUtYLzsGc7Hhn5xAV1rTJmpy6JZ is an address of mine that has four inputs, one for .45, one for .36, one for .015 and one for .01 BTC.

When I tried to send amounts under .45, it always proposed that it spend the .45 input except when the amount of the transaction was the exact amount of the transaction. When I attempted to spend the exact amount of the transaction, it would use the input that exactly matched the size. The same is true when I tried spending amounts greater then .45 but less then .81 BTC, when I attempt to send an amount of .45 plus the size of another input (except the .015 input) it would use those two inputs, otherwise it would use the .45 and the .36 input. I am not sure why it did not want to spend the .015 input unless it had to.

This leads me to believe that it will attempt to structure transaction in a way so that it will need to spend as little as possible on a TX fee (e.g. it wants to make the transaction size as small as possible).

It is note worthy that all the inputs are roughly the same age (within a week of each other) and I am not sure how it would react if the inputs were of significantly different ages (old inputs are generally more eligible to send free transactions as per most rules that most miners follow). One downside to this however may result in in you eventually having very small inputs if you do not spend exact amounts that you receive (IMO it is not the expected behavior for people to spend exact amounts they receive) which will potentially lead to very high TX fees for blockchain.info users if the use the same wallet long enough.

Thanks, that would be great.

I am fairly certain that they will only use the necessary inputs. Although they may use the smallest inputs and then move to larger inputs as necessary which may make it look like they are using all inputs depending on the inputs in your address.

Both using all inputs and using the smallest inputs first will most likely result in you having to pay less in tx fees over the long run.

If you give me a few hours I will take a look and test my theory.

I think this is what they do by default.

Unspent outputs, no. However you can structure transactions such that you spend all inputs in a specific address to avoid address reusing.

My understanding is that they will structure the transaction so that the tx fee will be smallest for the subject transaction (at least from what I can tell).

not sure..
but i think this is an automated process..
and so
you can not configure it..

Is there a way to choose which unspent outputs are included in a transaction?
Not sure, but it looks like it always includes all unspent outputs, even when not necessary. I guess it's trying to avoid address reuse?
Thanks