| === _mup__ is now known as _mup_ | |
| === zz_mwhudson is now known as mwhudson | |
| [22:12] <fwereade> waigani___, heyhey | |
| [22:12] <waigani_____> fwereade: hello :) | |
| [22:13] <fwereade> waigani___, how's it going? | |
| [22:13] <waigani_____> getting there | |
| [22:13] <fwereade> waigani___, sorry I haven't really said hi properly since you joined :( | |
| [22:13] <waigani_____> a LOT of code to get my head around! | |
| [22:13] <fwereade> waigani___, ha, yes indeed | |
| [22:13] <waigani_____> no problem, totally understandable | |
| [22:13] <waigani_____> ditto, sorry for not saying hi :) | |
| [22:14] <waigani_____> so, I'm getting racy hey? | |
| [22:14] <fwereade> waigani___, I'm kinda going to bed shortly but I just wanted to chat briefly about the set environ config stuff | |
| [22:14] <waigani_____> sure | |
| [22:17] <waigani____> fwereade: hangout or irc? | |
| [22:17] <fwereade> waigani___, the issue is mainly that I don't really want it to be possible to set an invalid environ config, and I am not convinced that it's possible to guarantee the sanity of a given change without (1) validating the change from the previous version --which is fine, you do it-- and (2) asserting in state that the previous version, from which the change is known to be valid, still applies | |
| [22:17] <fwereade> waigani____, I think I can irc it, I will be off to bed in a mo | |
| [22:18] <waigani____> ok | |
| [22:18] <fwereade> waigani____, does that make sense at first reading or shall I expand a little? ;) | |
| [22:19] <waigani____> right, so the real issue is the last one | |
| [22:19] <waigani____> how do you ensure the oldconfig is itslef valid | |
| [22:19] <fwereade> waigani____, if you can guarantee every change is valid, I think yu can guarantee that the previous version was | |
| [22:20] <fwereade> waigani____, because you cannot bootstrap but with a valid config | |
| [22:20] <waigani____> can we? | |
| [22:20] <waigani____> right | |
| [22:20] <waigani____> in which case the current method works then? | |
| [22:21] <waigani____> we can rely on an oldconfig | |
| [22:21] <waigani____> oohhhh | |
| [22:21] <waigani____> lol | |
| [22:21] <waigani____> i see | |
| [22:21] <waigani____> THAT is why you don't want to allow setconfig without validating | |
| [22:22] <fwereade> waigani____, the current method is (at least in theory) crack, because the *actual* change we end up making is pretty random -- see state/state.go:264 | |
| [22:23] <waigani____> so this is the race condition you mentioned? | |
| [22:24] <fwereade> waigani____, in *practice* it's usually ok, but that's because we don't get many concurrent updates to environ config | |
| [22:24] <fwereade> waigani____, yeah, I think so | |
| [22:24] <fwereade> waigani____, I have a tendency to froth about a wide range of possible race conditions | |
| [22:24] <waigani____> heh | |
| [22:25] <fwereade> waigani____, ah, but, yes, that's the one | |
| [22:25] <fwereade> waigani____, so what's interesting is that axw is doing some work that involves using an Environ inside state | |
| [22:25] <waigani____> what does axw mean when he says The settings changes are actually applied as a delta to what's on disk | |
| [22:26] <waigani____> "applied as a delta"? | |
| [22:26] <fwereade> waigani____, there's a Settings type | |
| [22:26] <fwereade> waigani____, it was written in python for zookeeper and ported straight without much consideration for whether it still makes sense | |
| [22:26] <fwereade> waigani____, hint: it doesn't | |
| [22:26] <waigani____> lol, okay... | |
| [22:27] <fwereade> waigani____, I am struggling to remember the *exact* details | |
| [22:27] <fwereade> waigani____, but it is itself fundamentally racy | |
| [22:27] <waigani____> don't worry, I'll follow up | |
| [22:27] <fwereade> waigani____, it reads existing state, calculates delta, applies delta | |
| [22:27] <waigani____> now I know the direction to look in | |
| [22:28] <fwereade> waigani____, pretty sure it doesn't assert the base state still holds | |
| [22:28] <waigani____> now state == mongodb? | |
| [22:28] <fwereade> waigani____, yeah, take a look at that for a bit of context | |
| [22:28] <fwereade> waigani____, yep | |
| [22:28] <waigani____> i.e. config stored in mdb | |
| [22:29] <fwereade> waigani____, but have a word with axw, because *he* is doing some work that involves using an Environ inside state to check sanity of AddMachine ops by checking with the provider | |
| [22:29] <fwereade> waigani____, and *you* are doing something that involves checking sanity of applying changes to Environ (configs) | |
| [22:30] <waigani____> will do. | |
| [22:30] <waigani____> would you like to see the ApplyAndValidate method I've refactored out, added back into SetEnvironConfig? | |
| [22:31] <waigani____> Such that you cannot set an environ config without validating it? | |
| [22:31] <fwereade> waigani____, I think that is at least part of it, but be suspicious of what actually happens when you try to use that settings type | |
| [22:32] <waigani____> fwereade: be suspicious of SetEnvironConfig? | |
| [22:32] <fwereade> waigani____, it may be that you're best off using entirely different code that just happens to use the same data format | |
| [22:32] <fwereade> waigani____, more of state.Settings | |
| [22:33] <fwereade> waigani____, ...or, heh, maybe converting it to use a new data format | |
| [22:33] <fwereade> waigani____, I'm also pretty sure that the fields are dumped straight into the mongo document | |
| [22:33] <waigani____> fwereade: just saw your comment: TODO(fwereade) state.Settings is itself really problematic in just about every use case | |
| [22:33] <fwereade> waigani____, and by sheer conincidence magic fields like txn-revno happen not to collide with actual env settings | |
| [22:34] <fwereade> waigani____, I think what I'm saying is that you have stumbled into a rabbit hole | |
| [22:34] <fwereade> waigani____, do not feel obliged to fix everything | |
| [22:34] <waigani____> I was just about to say the same! | |
| [22:35] <fwereade> waigani____, but be careful to understand what you're fixing and what you're not, and please document it clearly | |
| [22:35] <fwereade> waigani____, take heart: you're unlikely to make that specific code *worse* | |
| [22:35] <waigani____> obviously my understanding is cursory, so I'll follow up with axw and look into state.Settings | |
| [22:35] <fwereade> waigani____, and I'll be happy if it just gets a little bit better | |
| [22:36] <fwereade> waigani____, awesome, thanks | |
| [22:36] <waigani____> are there any other hits for me? | |
| [22:36] <waigani____> bits of code I should look at? | |
| [22:36] <fwereade> waigani____, for this particular stuff it's quite localised | |
| [22:37] <fwereade> waigani____, there are a couple of other Settings clients | |
| [22:37] <fwereade> waigani____, one day we'll get rid of them all | |
| [22:37] <waigani____> okay | |
| [22:37] <fwereade> waigani____, but it's the env config that really upsets me | |
| [22:38] <fwereade> waigani____, because it's the most potentially horrible one ;) | |
| [22:38] <fwereade> waigani____, anyway I should get some sleep | |
| [22:38] <waigani____> just before you go .... :D | |
| [22:38] <fwereade> waigani____, I might be a little late tomorrow, but dimitern is staying here, so if you see him and want to talk to me tell him to come shout at me :) | |
| [22:39] <fwereade> waigani____, I'm still here :) | |
| [22:39] <waigani____> could you give me one example of the race conditon? | |
| [22:39] <waigani____> two clients trying to set the config at the same time? Is that right? | |
| [22:39] <fwereade> waigani____, yeah | |
| [22:40] <waigani____> clients = machine agent, juju cli, ... | |
| [22:40] <fwereade> waigani____, ah! | |
| [22:40] <fwereade> waigani____, there *is* a replaceSettingsOp func | |
| [22:40] <fwereade> waigani____, that I think is not racy | |
| [22:40] <waigani____> oh | |
| [22:40] <fwereade> waigani____, it may need to be retried | |
| [22:40] <fwereade> waigani____, but if you use it the txn will abort | |
| [22:41] <waigani____> okay, lots to learn ... I'll let you sleep | |
| [22:41] <fwereade> waigani____, so, *if* you can construct a known-valid config, you can use replaceSettingsOp to be sure it actually lands in state | |
| [22:41] <waigani____> thanks for taking the time to walk me through the rabbit whole, a little ;) | |
| [22:41] <fwereade> waigani____, but to construct a known-valid one inside state, you'll need to talk to axw | |
| [22:41] <waigani____> *hole | |
| [22:41] <fwereade> waigani____, because | |
| [22:41] <fwereade> (you're sitting down, right) | |
| [22:42] <waigani____> hehe yep | |
| [22:42] <fwereade> waigani____, just because it's a valid config.Config | |
| [22:42] <fwereade> waigani____, it is *not* necessarily a valid config for any given provider | |
| [22:42] <waigani____> ugh | |
| [22:42] <fwereade> waigani____, let alone a valid change for that specific environ | |
| [22:42] <waigani____> what? | |
| [22:43] <waigani____> I get that it might not be valid for other providers | |
| [22:43] <fwereade> waigani____, simplest case: some fields are immutable, or should be | |
| [22:43] <fwereade> waigani____, change an env's name from foo to bar, bad things will happenb | |
| [22:43] <fwereade> waigani____, constructing an env, and setting the new config, *should* catch all those cases | |
| [22:43] <waigani____> so that should be caught as invalid by the environ provider validator? | |
| [22:44] <waigani____> right | |
| [22:44] <fwereade> waigani____, *but* the environs package uses the state package, so you can't directly reference an Environ as such from code inside state | |
| [22:44] <fwereade> waigani____, axw is dealing with *exactly* the same problem, creating environs inside state to validate machine addition | |
| [22:45] <fwereade> waigani____, so it would be good if your solutions were roughly aligned :) | |
| [22:45] <fwereade> waigani____, was that a bit more helpful? | |
| [22:46] <waigani____> yes, you've set me in the right direction | |
| [22:46] <fwereade> (ok, it's not *exactly* the same problem, but you can surely talk productively) | |
| [22:46] <waigani____> I'll go annoy axw now ;) | |
| [22:46] <fwereade> waigani____, cool, cheers | |
| [22:47] <waigani____> thanks again, sleep well | |
| [22:47] * fwereade disappears | |