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The original was posted on /r/mysql by /u/emsai on 2023-08-04 16:41:34+00:00.

Have imported the data into a large table while accidentally missing the id/autonumber filed. (250M records)

The import process went blazing fast which shocked me. I mean it’s expected since no index build, but the difference in time was huge.

Q: What are some caveats of not using PK?

Also, How does MySQL handle this?

Note, our queries don’t need PK but depend mostly on a field that contains an int/ hash.

Context: I’m interested in both InnoDB and MyISAM as this particular table might be a good contender for MyISAM (load once, read only table).

Thanks!