Document logging options (via DEBUG env var)

[nikolasburk]

When using Prisma Client, you can set different log levels via the DEBUG env var. This needs to be documented. Eg.: DEBUG=prisma-client or DEBUG=*

[pantharshit00]

We use the popular nodejs logging library debug: https://www.npmjs.com/package/debug

Many other packages like express also use the same library. So when you initialize debug, you give your debugger a namespace like shown below:

const debug = require('debug')('prisma-client')

and it is shown in the debug output when you enable it via the DEBUG environment variable:

So DEBUG=* enables all the debug loggers and DEBUG=prisma-client only enables the debug output for Prisma namespace. The two major namespaces that we use in the client right now are prisma-client and engine so you can only enable debug output from these using DEBUG=prisma-client,engine.

Also, if you want to force the debug output regardless of the DEBUG env, you can pass the debug option in the Prisma client constructor like so new PrismaClient({ __internal: {debug: true}})

[nikolasburk]

Documented via: https://github.com/prisma/prisma2/pull/1801/files