Clarification on “Call Me Maybe: MariaDB Galera Cluster”

Post by bsaul » Fri, Sep 18, 2015, 1:23 PM UTC

ealexhudson wrote: post #9

bsaul wrote: post #5

Earlier quoted context omitted.

Good point, but imho anyone that relies on transactionnal properties to ensure validity of its operation should really not be using ORMs ( at least not for the sensitive operations). You shouldn't need to read an ORM documentation to understand what kind of locking is happening at a given time. It should all be there right in your code.

This approach only works if your logic is codable in SQL format in the way this trivial balance change can be. If the change is happening in app business logic, this is always going to be a problem. The fact the balance+=25 type approach works is kind of a hack, and I don't think Aphyr is wrong to call it "corrupted" (in this specific example, in one transaction, you could say that it is inconsistent - but you only n…

Post by pricechild » Fri, Sep 18, 2015, 1:32 PM UTC

michaelt wrote: post #6

tptacek wrote: post #3

I do not quite like the usage of the word “corrupted” here. For me, the more correct word be to use is “inconsistent”. Aren't we talking about situations in which a database tracking account balances creates money out of thin air, or vaporizes it unexpectedly? I feel like Aphyr is always at pains to talk about the real-world implications of these findings --- not just how bad they are in sensitive applications, but a…

A database maker would say it isn't the database that created the money out of thin air, but the faulty application code that didn't select the right isolation level. Of course, whether it's wise for a database to default to anything except Serializable isolation is another matter.

Post by AlisdairO » Fri, Sep 18, 2015, 1:38 PM UTC

inversionOf wrote: post #28

AlisdairO wrote: post #22

Edit: ignore this, it's addressing a completely different situation, and I clearly didn't read the article well enough. The code in the article writes all of the locations it reads, so true SI ought to keep you safe. My apologies! Yet another edit: huh, it seems that InnoDB in RR doesn't rollback when you write to a row that's been written since you started the transaction. TIL. -------- It's worth noting here that (…

it doesn't guarantee that the data in the DB itself has stayed constant By definition, snapshot isolation is supposed to guarantee that all reads are the consistent, committed data as of the begin transaction, and the commit will fail and rollback if any data altered within a snapshot isolation transaction was already changed. The response by Percona, unless I am reading it wrong, actually agrees that they are not tr…

Post by dbarlett » Fri, Sep 18, 2015, 1:52 PM UTC

infinotize wrote: post #34

Besides being a super well-written and interesting series technically, the Call Me Maybe blogs have been very revealing as far as different organizations' response to criticism. Especially considering all of the target applications are open source, the project maintainers should be profusely thankful someone has taken the time for such thorough analysis, presumably much deeper than the maintainers themselves appear t…

    How a project performs today tells you the zeroth derivative of its location.
    Looking at the commit log tells you about the first derivative. How people react
    to Call Me Maybe when its about their product gives you a lot of information
    about the second derivative.

Post by seiji » Fri, Sep 18, 2015, 2:06 PM UTC

dbarlett wrote: post #37

infinotize wrote: post #34

Besides being a super well-written and interesting series technically, the Call Me Maybe blogs have been very revealing as far as different organizations' response to criticism. Especially considering all of the target applications are open source, the project maintainers should be profusely thankful someone has taken the time for such thorough analysis, presumably much deeper than the maintainers themselves appear t…

I really like jerf's take on it [1]: How a project performs today tells you the zeroth derivative of its location. Looking at the commit log tells you about the first derivative. How people react to Call Me Maybe when its about their product gives you a lot of information about the second derivative. [1] https://news.ycombinator.com/item?id=10082099 Edit: username