storeUser, called from stream.js, produces duplicate record errors

[jsha]

There's a race condition in storeUser: first it tries to load a user from the DB if it exists; Otherwise it creates one. In low traffic this isn't an issue, but in stream.js often there are multiple very closely-spaced calls to storeUser for the same user.

Options:

• Figure out if Sequelize supports some sort of 'ignore duplicates' on save. They definitely do for bulkCreate; The docs don't indicate anything on .save, but there might be something undocumented.
• Make stream.js more selective about when it stores users, decreasing the chance of hitting this issue. For instance, maybe only store a user if it already exists in the DB and previously had deactivatedAt set. This way when a user gets unsuspended we record that fact as soon as possible. This has the side benefit of reducing the amount of work stream.js has to do, which can be a lot.
• Keep an in-memory map of which users have a storeUser in progress at any given time.

[jsha]

Updated title to better reflect what happens when this occurs. MySQL generates an error because of a duplicate primary key (uid), which winds up in the logs. Harmless, but obscures other, real errors in the logs. So maybe one other approach: If there's an error from the sequelize save command, don't bother logging it, or log it at INFO or even DEBUG level.

[jsha]

Fixed.