user2075: Say for an exchange that manages thousands of users, and each transaction needs a new receiving address, how much space would thier wallet(s) take. 
I am assuming 100000 users and each user would have about 10000 transactions, so there are about 10^9 keys to be stored. For safety, we would say there are 10^10 keys max that may be stored. 
All I need to know is the size of one key stored in the wallet. 

user888: The bitcoinj private keys are 32 bytes long. You would also want some sort of indexing around them so that you could access them efficiently.
If you used a deterministic wallet you would only need one seed and a chain code per customer and generate the addresses as required. I think they are typically 32 or 64 bytes long. 

2075: <p>Say for an exchange that manages thousands of users, and each transaction needs a new receiving address, how much space would thier wallet(s) take. </p>

<p>I am assuming 100000 users and each user would have about 10000 transactions, so there are about 10^9 keys to be stored. For safety, we would say there are 10^10 keys max that may be stored. </p>

<p>All I need to know is the size of one key stored in the wallet. </p>
 888: <p>The bitcoinj private keys are 32 bytes long. You would also want some sort of indexing around them so that you could access them efficiently.</p>

<p>If you used a deterministic wallet you would only need one seed and a chain code per customer and generate the addresses as required. I think they are typically 32 or 64 bytes long. </p>
