171–180 of 303 posts
Why do "self posts" like this show up in the same light gray as posts with negative vote counts? My eyes aren't great and I find it hard to read
Amazing that such a large percentage of debugging involves determining exactly what you are debugging. The definition of the problem, many times, is the solution. Might be a good time to mention Rubber Duck Debuggging. http://en.wikipedia.org/wiki/Rubber_duck_debugging
A few times a month, I'll look up at one of my colleagues and say, "hey, got a sec? I need to talk to the duck," and they know this means I'm going to talk to their head but they can basically keep doing what they're doing and nod occasionally. This serves several purposes: (1) It's less insane-sounding than actually talking to an inanimate object in an open work environment. (2) It actually feels better and forces m…
Amazing that such a large percentage of debugging involves determining exactly what you are debugging. The definition of the problem, many times, is the solution. Might be a good time to mention Rubber Duck Debuggging. http://en.wikipedia.org/wiki/Rubber_duck_debugging
If you don't understand your problem, you can't make a plan. If you can't make a plan, you can't execute it.
Another interesting lesson from that book is that one should spend time on evaluation (how did this come about? Could We have fixed this sooner? How are we going to prevent it in the future?)
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Extremely appropriate as Fry is his own grandfather and the site software can't handle that relationship.
That's one of my favorite lines from Futurama, 'Ohh, a lesson in not changing history from Mr. "I'm My Own Grandfather"!'
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Databases, at least the SQL kind, really aren't good at dealing with hierarchical data, and I don't know how you'd even begin to express that kind of constraint. I don't think a traditional database is the answer here. (If it were me, once I'd done it more than twice I'd write a "move thread" admin tool in the UI, and after I screwed it up like this I'd have a place to add such a check to).
If you were using some kind of representation for Nested Sets -- left-to-right depth-first numbering, or a human-readable id.id.id chain -- then it's really easy to write a constraint for that: parent left myright, or dotted_id.split('.').filter{|first, rest| return false if rest.contains first} (yeah, yeah, that second pseudocode would be unrealistically PITA for some DBs). More generally: I'm not a big SQL wonk any…
One way involves accumulating an array of nodes already visited as the tree gets walked, checking each node as-visited for membership in the array-to-date.
The other method, a bit more of a hack, is just adding a LIMIT clause.
I think the 'WITH' clause is a great addition to the SQL standard, very much worth the learning the weirdness of its syntax and its optional 'RECURSIVE' term (which, as the Postgres documentation points out, isn't really recursion, it's iteration).
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I disagree. Very few companies would think negatively of an engineer if they made such a mistake on a non-essential, non-revenue-generating fun/research project. How many dollars did YC lose because of the outage? None. (Maybe they saved a few on bandwidth!) I also predict that exactly zero startups will say, "Man... I'm not going to take seed money from those guys! They had discussion forum downtime."
They could save even more if they shut it down! That's a ridiculous thing to say. We could all save money that way. You've obviously never worked in a for profit corporation. in such there are policies and practices put in place to prevent just this kind of newbie mistake. You never modify the live database directly. Never ever. Whether it's a bottom line property or not. I didn't say it would negatively impact YC's…
It really depends on what kind of business you're in whether this is acceptable or not.
I'm not sure whether it's terrifying or relieving to realize that if all I dream of comes to pass and I achieve something akin to the legendary status of pg in the hacker community that I will still be susceptible to the inevitable facepalm moments that come with direct database access. In any case I am thankful for the detailed explanation.
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The kind of assertion he needed could not be ensured by the database. The kind of assertion he needed was there are no cycles in the graph. How would you ensure that in a database? Also, HN uses flat files, not database.
A constraint on the parent-child link table "Child creation time stamp > Parent creation timestamp" would do it. Might not be a bad idea, if the site were to have the two requirements "maintenance must be done on the live site from a repl" and "5 nines availability".
create table post (id int primary_key, parent_id int references post(id), child_id int references post(id), created_at timestamp)
I am not saying this can't or shouldn't be done. I am saying a db won't directly solve it.
However, you example will work perfectly for enforcing constraints in the code via the mutator which can compare child and parent timestamps, provided pg was doing it via a mutator, and not directly changing the ids.
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A few times a month, I'll look up at one of my colleagues and say, "hey, got a sec? I need to talk to the duck," and they know this means I'm going to talk to their head but they can basically keep doing what they're doing and nod occasionally. This serves several purposes: (1) It's less insane-sounding than actually talking to an inanimate object in an open work environment. (2) It actually feels better and forces m…
On occasion, I'll write a question on stackoverflow and re-read it a few times before hitting submit just in case I get that eureka moment. I think I've written way more non-submitted questions than submitted questions.