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Why HN was down

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Re: Why HN was down

#191

Post by irahul »

lmm wrote: post #117
chernevik wrote: post #95

Earlier quoted context omitted.

I am but an egg, I have two questions. One, if the data were held in a database, should a change like this be captured in the database logs? I am seeing more and more situations where I want these, I notice that they are by default turned off for mysql and wonder if this reflects a de facto judgment that logging slows performance more than is usually worthwhile. Two, if the data were kept in a database, wouldn't some…

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).

I think if you want the family tree, you can write a self referential(assuming post table is self referential as it should be) recursive query.

But in this case, writing a before insert/update trigger which ensure some_post.created_at < parent.created_at before setting parent.parent_id = some_post will do the trick.

Re: Why HN was down

#192

Post by lifeisstillgood »

wpietri wrote: post #113
luser001 wrote: post #89

Earlier quoted context omitted.

> I eventually realised that typing sudo every time he touched a box was no defence against doing the wrong thing. IIRC, sudo logs all commands to syslog. Which might come in handy. Yes, root commands will be logged by bash to .bash_history, but there are limits of # of commands lots, what happens if you are logged in multiple times into same account etc. Anyway, that's why I like sudo.

Beyond the logging, which I love, I use it for the differentiation of states. I'm just a little more attentive when I type "sudo" before something. At work, a relatively young engineer accidentally typed a command meant for a test database server into a production window. There was a big rush to restore from backups, and there was a small amount of data loss. One thing that came out of the retrospective, requested by…

I have tried the red / green console but never a pirate hat.

My son now definitely thinks work is like his school :-)

Re: Why HN was down

#193

Post by irahul »

swah wrote: post #66
irahul wrote: post #35

Earlier quoted context omitted.

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.

I was thinking something like (supposing the comments were stored as "closure tables" like Karwin suggests): CREATE TABLE comment_tree ( ascestor_id REFERENCES comments(id) NOT NULL, descendant_id REFERENCES comments(id) NOT NULL, CHECK ( ascestor_id descendant_id ) ) but I'm probably overlooking something. (I'm aware that HN uses flat files, I was just making a counter-point to the "simple assert" solution...)

That will prevent a child being its own parent. It won't work for more than one level i.e a post being its own grandchild. Assume (post_id, parent_id) sequence: (1, 3) -> (2, 1) -> (3, 2).

Re: Why HN was down

#194

Post by emillon »

tolmasky wrote: post #106

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

The rationale for this is that if you need to post a long text post, it should be in the form of a blog post instead. I agree with you that it's not really adapted for a meta post.

Re: Why HN was down

#195

Post by yuhong »

kamjam wrote: post #167
larrys wrote: post #83

Earlier quoted context omitted.

I find that if I am doing something "dangerous" (example might be using power tools) I have to say to my self "be careful this is dangerous" to avoid being on autopilot and making casual errors. Maybe a better example is the way you train yourself after you've picked up a box the wrong way and pull something to try to remember each and every time to watch your specific movements.

But at some point, you will become complacent, and it will taken a mistake to remind yourself again. We've all done it. I shut down an NT4 production server because I was connected via remote desktop and clicked shutdown rather than log off. This was back in the day when there was no pop-up asking for reason you want to shut down and confirmation. Luckily it was just our internal intranet server!

You were running NT4 Terminal Server Edition?

Re: Why HN was down

#196

Post by philsnow »

lifeisstillgood wrote: post #67

There are a number of comments that add up to "what steps will you take to ensure this does not happen again" - akin to a incident review. As speculation that's fine, as advice, I don't think it should be listened to. I am reminded of an long-in-the-tooth sysadmin of my acquaintance who logged in everywhere as root. His theory - "they are my boxes. I screw it up, I fix it." I eventually realised that typing sudo ever…

s/anime/animus/ ? or is this a new usage of "anime"?

Re: Why HN was down

#197

Post by kamjam »

cientifico wrote: post #181
kamjam wrote: post #163

Earlier quoted context omitted.

This is so true, probably about 90% of the time my colleagues call me over about a problem they are facing, explain in detail what the problem is and then eureka! Most of the time it would actually take me much longer to figure out the exact issue since I don't know the ins/outs and subtleties of the code but it's exactly as you say. Of course, it makes me look really good cos I just "helped" them solve their issue :…

Maybe because the solution is in asking the good questions.

Yup, for sure it is, sometimes just having someone else there and having to run through all the steps for them points out the obvious. There was another user further down that said he solved a lot of his own problem just typing them out with enough detail to be able to post on StackOverflow. Same principle.

Re: Why HN was down

#198

Post by mafro »

3pt14159 wrote: post #183
lmm wrote: post #115

Earlier quoted context omitted.

Typing sudo won't save you, but using a higher-level interface will. Everyone I've ever known to change something in the database by hand, everyone at all, even on a hobby project that they know like the back of their hand, has screwed it up sooner or later. At some point the pain tells you you should stop doing that, and you create an admin tool that lets you do what you need to repeatably and safely.

I've never screwed it up on a live database, but I do take about 5 mins, first reviewing the keys, the type, whether or not something can be null, checking to see if critical columns have select count(distinct column_name) having count(distinct column_name) > 1; To make sure that there isn't an underlying uniqueness assumption. Sure I could do it in 10 seconds and save myself 290 seconds (a 97% savings!) but then one…

This. Back in the day when I was in more of an analyst role, I ended up /having/ to hack on the live DB frequently (reasons for this were myriad).

1. Always, always make a backup just before the hack.

2. Write a small set queries like 3pt14159's to check uniqueness and other pertinent properties.

3. Write a SELECT query to show the data you are going to change.

4. Borrow the WHERE clause from 3, and write your UPDATE statement.

5. Run 4, and then run 3 again to see that you successfully fixed it.

6. When it goes wrong, restore the backup from 1 :0

Re: Why HN was down

#199

Post by brehaut »

robinh wrote: post #174
Aardwolf wrote: post #142

Earlier quoted context omitted.

That's one of my favorite lines from Futurama, 'Ohh, a lesson in not changing history from Mr. "I'm My Own Grandfather"!'

Curiously, that episode was on TV where I live just an hour ago.

http://en.wikipedia.org/wiki/Pareidolia
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