user2995: We use the standard client in our business. The wallet already contains about 25k addresses. Will the wallet remain stable after the number reaches 100k or a million addresses? I was told that all major business have forked the client. Should we also fork and code our own wallet?

user-1: It all comes down to historical data. Do you retrieve historical data by querying the blockchain or do you rely on your own transactional data in a local DB? If you do the latter and you are concerned about the stability of your overloaded wallet you can always switch to a brand new, clean wallet with only the preloaded 100 addresses and be confident that up to the 25K point everything will be smooth and running. 

user9563: Regular BitcoinQT client is not suited to run a huge amount of addresses/transactions.
The database easly goes to the roof in a month with IO operations, if you do, let's say, 1 transaction per minute. 
Please consider reading blockchain directly, or use external service, which will handle the overhead for you, ie. Blockchain.info

user11581: I tested this by programatically adding 1 million addresses to the QT client via the JSON-RPC interface from a Java program. Rescanning was turned off so all it did was add the addresses and not confirm the balances. It took around 24 hrs to add 1 million addresses and then it took another 4 hrs or so to restart the client and scan the 1 million addresses. I was using a MacBook Air so not very powerful hardware. Still, given the amount of time it took to do the rescan I would not recommend using the QT client with that many addresses in a production setting. Good luck.

user11369: I've ran tests before on .5 million addresses generated in one afternoon. It fired walletnotify within the milliseconds, no noticeable delay when I sent an amount to a random address. Only noticeable thing was that the client took 30 minutes to start up, which I guess is fine if you run a larger service. Only thing that may trouble you is slow transaction creation time, but someone on here advised me to just move the funds into a new address monthly.

2995: <p>We use the standard client in our business. The wallet already contains about 25k addresses. Will the wallet remain stable after the number reaches 100k or a million addresses? I was told that all major business have forked the client. Should we also fork and code our own wallet?</p>
 -1: <p>It all comes down to historical data. Do you retrieve historical data by querying the blockchain or do you rely on your own transactional data in a local DB? If you do the latter and you are concerned about the stability of your overloaded wallet you can always switch to a brand new, clean wallet with only the preloaded 100 addresses and be confident that up to the 25K point everything will be smooth and running. </p>
 9563: <p>Regular BitcoinQT client is not suited to run a <em>huge</em> amount of addresses/transactions.
The database easly goes to the roof in a month with IO operations, if you do, let's say, 1 transaction per minute. 
Please consider reading blockchain directly, or use external service, which will handle the overhead for you, ie. Blockchain.info</p>
 11581: <p>I tested this by programatically adding 1 million addresses to the QT client via the JSON-RPC interface from a Java program. Rescanning was turned off so all it did was add the addresses and not confirm the balances. It took around 24 hrs to add 1 million addresses and then it took another 4 hrs or so to restart the client and scan the 1 million addresses. I was using a MacBook Air so not very powerful hardware. Still, given the amount of time it took to do the rescan I would not recommend using the QT client with that many addresses in a production setting. Good luck.</p>
 11369: <p>I've ran tests before on .5 million addresses generated in one afternoon. It fired walletnotify within the milliseconds, no noticeable delay when I sent an amount to a random address. Only noticeable thing was that the client took 30 minutes to start up, which I guess is fine if you run a larger service. Only thing that may trouble you is slow transaction creation time, but someone on here advised me to just move the funds into a new address monthly.</p>
