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While interviewing candidates at my last gig, I was taken aback by how many of them confused consistency with isolation in databases. Most who came from a Mongo

by cwojno 7y ago

While interviewing candidates at my last gig, I was taken aback by how many of them confused consistency with isolation in databases. Most who came from a Mongo background did not understand isolation at all and confused it with consistency. Concepts such as Optimistic locking and Pessimistic locking are also not well-known any more, either, much to my dismay :(

mehrdadn 7y ago
Were these for candidates who had previously claimed to know databases (or were applying for positions that assumed such knowledge)? Or did you expect this of all candidates?
- cwojno 7y ago
  Knowledge of SQL databases, specifically, was advertised and required by the recruiters, yes.
  - the_af 7y ago
    Knowledge of SQL databases at which level? DBA level? Programmer level? The distinction is important because when recruiters ask "do you know SQL databases?", 99% of the time they mean "have you used one, and can you write a query with joins?" or "do you know how to create indexes?". The almost never mean "do you understand how a database is implemented?" or "do you know the difference between consistency and isolation levels?".
the_af 7y ago
Why were you taken aback? From TFA: > "For many years, database users did not have to simultaneously understand the concept of isolation levels and consistency levels. Either a database system provided a correctness/performance tradeoff using isolation levels, or it provided a correctness/performance tradeoff using consistency levels, but never both. This resulted in a blurring of these concepts to the point that many people --- even experts in the field --- confuse isolation levels with consistency levels and vice versa. For example, this talk by a PhD student at Berkeley (incorrectly) refers to causal consistency as an “isolation level”. And this paper from well-known researchers at MIT and Harvard --- including a Turing Award laureate --- (incorrectly) call snapshot isolation and serializability “consistency” levels. I am confident that all these well-known researchers know the difference between isolation levels and consistency levels. However, as long as isolation and consistency could not be tuned within the same system, there has been little necessity for precision in the parlance around these terms." So I wouldn't say it's uncommon or unexpected of non-experts to confuse the two concepts...
- cwojno 7y ago
  This experience pre-dates the publication and my knowledge of the existence of this article. #timeTravelImpared
  - the_af 7y ago
    Haha, but seriously. I didn't mean why you were taken aback given this article; I meant why you were taken aback given most developers do not understand this distinction, seldom have the real need to, and even experts are fuzzy on the details. Maybe I misread your tone, but to me it was like "programmers don't know how to program" (like in the FizzBuzz anecdotes).

by cwojno 7y ago

mehrdadn 7y ago

Were these for candidates who had previously claimed to know databases (or were applying for positions that assumed such knowledge)? Or did you expect this of all candidates?

cwojno 7y ago
Knowledge of SQL databases, specifically, was advertised and required by the recruiters, yes.
- the_af 7y ago
  Knowledge of SQL databases at which level? DBA level? Programmer level? The distinction is important because when recruiters ask "do you know SQL databases?", 99% of the time they mean "have you used one, and can you write a query with joins?" or "do you know how to create indexes?". The almost never mean "do you understand how a database is implemented?" or "do you know the difference between consistency and isolation levels?".

the_af 7y ago

Why were you taken aback? From TFA: > "For many years, database users did not have to simultaneously understand the concept of isolation levels and consistency levels. Either a database system provided a correctness/performance tradeoff using isolation levels, or it provided a correctness/performance tradeoff using consistency levels, but never both. This resulted in a blurring of these concepts to the point that many people --- even experts in the field --- confuse isolation levels with consistency levels and vice versa. For example, this talk by a PhD student at Berkeley (incorrectly) refers to causal consistency as an “isolation level”. And this paper from well-known researchers at MIT and Harvard --- including a Turing Award laureate --- (incorrectly) call snapshot isolation and serializability “consistency” levels. I am confident that all these well-known researchers know the difference between isolation levels and consistency levels. However, as long as isolation and consistency could not be tuned within the same system, there has been little necessity for precision in the parlance around these terms." So I wouldn't say it's uncommon or unexpected of non-experts to confuse the two concepts...

cwojno 7y ago
This experience pre-dates the publication and my knowledge of the existence of this article. #timeTravelImpared
- the_af 7y ago
  Haha, but seriously. I didn't mean why you were taken aback given this article; I meant why you were taken aback given most developers do not understand this distinction, seldom have the real need to, and even experts are fuzzy on the details. Maybe I misread your tone, but to me it was like "programmers don't know how to program" (like in the FizzBuzz anecdotes).