Is it necessary to close bitcoin client before making a backup of wallet file?

[bitrebel]

I think I read somewhere that you have to close the bitcoin client before making a wallet file backup. Is this correct? 

[Maged]

It's a good idea. If closing Bitcoin is inconvenient, you should use the backupwallet RPC command. If you don't close Bitcoin and just copy the file, it's not guaranteed that the backup won't be corrupted.

[jackjack]

I don't think it's critical but as the client locks the wallet database, it's better to close it
Better safe than sorry

[randomguy7]

Good question. I wouldn't trust a wallet backup made while the client was running. I think the file could be in an inconsistent state if it was copied while the client was writing to it.
The next question is if the client can automatically fix such a wallet.dat and if only the new changes are lost or if it breaks the whole wallet.

[kjj]

If you use the backupwallet command, the client closes the wallet, flushes the write caches, makes a copy, and reopens it, so that you don't need to stop the client.