Database Reference
In-Depth Information
For the problem to occur, Step 4 must happen before Step 5: it's important that both pro-
cesses check the database for an existing row before either writes to the database. It's an
improbable scenario, in which two users would attempt to sign up with the exact same
username at roughly the exact same time, but it's not an impossible one. As our service
becomes more popular, we're more and more likely to run across such unlikely events, so
we're much better off with a system that guarantees that no new user account will over-
write an existing one.
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