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by uhoh-itsmaciek 2458 days ago
>I'm not sure about "non-trivial amount of data" - especially if we're talking about a single row (single user) here? I suppose there might be a few blolbs of large json documents? > >And I'm not sure I understand "repeating information in query results" - surely we're talking about receiving a query, transforming it and responding with the data?

For a query like

  SELECT u.* , c.* FROM users u INNER JOIN comments c
    ON u.id = c.user_id WHERE u.id = <...>
above, the user information is repeated for each comment, e.g.,

  u.id, u.name, c.id, c.text
  1     Bob     1     you are right
  1     Bob     2     you are wrong
  1     Bob     3     you are right again
If you have a hundred comments, and many user fields, this can be a significant amount of data to pass around. Or maybe this is not what you meant? I feel like we may be talking past each other. Can you give an example of what you think the ideal sql should be for "give me user with id = 1 and all their comments"?
1 comments
e12e 2458 days ago
No, you're probably right - I suppose the database drivers might naively serialize that in a one-to-one representation (to be honest, I've never really looked into the protocols that postgres or Ms sql use for transferring data).

I didn't consider the kind of expansion you're alluding to - on the other hand i can't ever remember seeing an indication that the amount of data returned is an issue with app performance.

But I've certainly seen the number of round-trips result in real issues. And complicated joins, for that matter.

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uhoh-itsmaciek 2458 days ago
I've worked on a few Postgres drivers and the protocol is basically sending data row-by-row, column-by-column. Sure, it could be more clever, but that's time and cpu and memory spent being clever instead of moving data.

But you're right, there are always trade-offs, and there are some situations where the current AR approach is not ideal, and a single join would be more efficient. However, I suspect this is the way AR does it because it's right enough often enough that it works well as the default approach.

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