How do sites like Coinbase and Bitstamp manage user accounts?

[drenation]

From what I've read about Bitcoind accounts https://en.bitcoin.it/wiki/Accounts_explained, it is extremely inefficient.

So I wondering, how do large sites like Coinbase and Bitstamp manage this?
Do they have just one large wallet file? Does every person get their own wallet, or are they making use of accounts? Or maybe they only keep track of what you 'own' and using a central wallet pay out when you request your coins? I'm not completely sure and this situation definitely perplexes me. Thanks

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[bassguitarman]

I could be completely wrong, but I believe that they have an internal ledger of balances. 

[Rannasha]

The typical approach is to assign a user a unique deposit address and once the software detects a new transaction to that deposit address, the account-balance is updated in the database of the site. The actual funds from all users are stored together and withdrawals will come out of this big stack.

[beachparty]

There is ledger, plus web interface can only read tables mostly

[Cryddit]

Unreliably, if the history of other exchanges is any guide.

Seriously, don't get goxxed.  Keep your wallet yourself, and absolutely no more than you're comfortable with strangers losing anywhere else.

Exchanges eventually get hacked.  Or Mismanaged.  Or whatever.  Let them hold 0.01 BTC or whatever to keep your account open, and keep the rest where nobody else's mistake can put it at risk.

I'll reconsider when the Federal Deposit Insurance Co.  Insures BTC balances and the bitcoin exchanges meet its security and liability requirements.  And I'm not expecting that to happen during the current decade.