Is a federated Twitter even possible?(venomousporridge.com)
venomousporridge.com
Is a federated Twitter even possible?
http://venomousporridge.com/post/30043951343/is-a-federated-twitter-even-possible
23 comments
551 words spilled on a simple question, with a simple, obvious answer: E-mail.
* Immediacy: if a post has been made by someone I follow, I can see it in my timeline right away (or close enough that I don’t notice the difference). "E-mail"
* Chronology: posts always appear in order by time posted. "E-mail". Chronology as the author imagines it doesn't even occur for Twitter, likely their machines' timestamps are fuzzy +/- perhaps up to a minute or more.
* Monotonicity: timelines grow only from the top; older posts are never retroactively inserted. So have your client mark a message by the time it's received, provide a second sort order. Ugh. "E-mail"
There are genuine technical challenges to implementing a robust many-many federated messaging system, this post mentions none of them.
* Immediacy: if a post has been made by someone I follow, I can see it in my timeline right away (or close enough that I don’t notice the difference). "E-mail"
* Chronology: posts always appear in order by time posted. "E-mail". Chronology as the author imagines it doesn't even occur for Twitter, likely their machines' timestamps are fuzzy +/- perhaps up to a minute or more.
* Monotonicity: timelines grow only from the top; older posts are never retroactively inserted. So have your client mark a message by the time it's received, provide a second sort order. Ugh. "E-mail"
There are genuine technical challenges to implementing a robust many-many federated messaging system, this post mentions none of them.
It's both possible and necessary. Think about it - even a centralized service like twitter or facebook will have many distributed & disparate services that need to work together to provide a feed. Hence, there probably already is some kind of federation going on, you just don't know it.
Source: I work @ LinkedIn on these types of problems.
Source: I work @ LinkedIn on these types of problems.
Author here: a few people have raised this point. Perhaps I should have made a distinction between "federated within the same data center" and "federated across the internet." They are two entirely different problems.
Also, didn't twitter release as OSS some sort of piping mechanism for exactly this?
If it was impossible for a federated network, it would also be impossible for Twitter. They can either guarantee that messages only show up at the top, or that messages always show up in order (meaning older posts get inserted into the middle of the timeline, as you eventually receive them).
Why couldn't the user decide how to view message?
You could easily allow a user to see messages ordered by "send time" or "received time". You could even add an "unread" flag to messages, so that unread messages show up first, then migrate to their proper locations in order.
Ya know... kinda like email.
You could easily allow a user to see messages ordered by "send time" or "received time". You could even add an "unread" flag to messages, so that unread messages show up first, then migrate to their proper locations in order.
Ya know... kinda like email.
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Sure, of course they could. The point is that you can't do both at the same time.
You can if you use vector clocks.
@sp332 You can prevent that by buffering messages. The less you tolerate messages appearing in-between messages you've seen before, the more you buffer. If the latency between your host and the host of someone you follow is high enough that it's taking more than a few seconds for you to get the message, they're effectively down. Late is better than never.
@sp332 You can prevent that by buffering messages. The less you tolerate messages appearing in-between messages you've seen before, the more you buffer. If the latency between your host and the host of someone you follow is high enough that it's taking more than a few seconds for you to get the message, they're effectively down. Late is better than never.
Vector clocks are only a partial ordering. You'd still have old events popping into the middle of your timeline.
Right, but since Twitter manages all of Twitter's servers (and the dedicated low-latency network via which they're presumably all connected) they can satisfy both of these constraints without sacrificing the third (immediacy). I'm speculating here, but I think that's why it takes a few seconds to post a tweet: it's propagating across the internal federation so that all the nodes have it before it "goes live."
To be specific, your tweet is not timestamped when you send it. It only gets an "official" timestamp when twitter decides to give it one, after receiving it. That means Twitter arbitrarily sets the timestamp whenever they get around to shoving it on top of your feed. So they do have the problem of tweets arriving out of order (due to network latency etc), they just hide it by rewriting timestamps!
eta: I admit this is a smaller problem for a centralized service than a federated one, but I would argue that it can work "well enough".
eta: I admit this is a smaller problem for a centralized service than a federated one, but I would argue that it can work "well enough".
How is twitter immediate when it's down?
Twitter doesn't solve the immediacy problem with any hard guarantees either.
Most of the time email is on par with twitter.
Twitter doesn't solve the immediacy problem with any hard guarantees either.
Most of the time email is on par with twitter.
Huh? When Twitter's down, no one can post, so immediacy is meaningless. This is like saying "my car's faster than yours after yours hits a tree."
Except that twitter does go down, so if you had a distributed car that was incapable of hitting a tree it would be an advantage.
The situ with email is that at any moment the system is up but individual nodes may be unreachable or delayed, conversely if twitter is up all nodes are reachable in constant time, but if it's down all nodes are unreachable.
In real systems these two properties are mean virtually the same thing, at any given point in time your party may or may not be reachable with a given latency.
The situ with email is that at any moment the system is up but individual nodes may be unreachable or delayed, conversely if twitter is up all nodes are reachable in constant time, but if it's down all nodes are unreachable.
In real systems these two properties are mean virtually the same thing, at any given point in time your party may or may not be reachable with a given latency.
Isn't OStatus exactly this, or does it fail one of his criteria?
http://en.wikipedia.org/wiki/Lamport_timestamps
Edit: More information on how to actually use Vector Clocks (which are sort of like multi-way Lamport Clocks) in a real system: http://basho.com/blog/technical/2010/04/05/why-vector-clocks...
Edit: More information on how to actually use Vector Clocks (which are sort of like multi-way Lamport Clocks) in a real system: http://basho.com/blog/technical/2010/04/05/why-vector-clocks...
Is the web federated? Everyone hosts their own sites and there are several browsers -- I don't see why we can't have a social media version of this.
Who gets to host #beiberfever?
You can build a distributed system that has hashtags (ex: by using a DHT to map tags to lists of nodes that act as clearinghouse for messages with those tags) but that system is not the web.
You can build a distributed system that has hashtags (ex: by using a DHT to map tags to lists of nodes that act as clearinghouse for messages with those tags) but that system is not the web.
The web is not "federated": site A does not communicate with site B. Contrast with SMTP or XMPP which require federated servers to communicate with one another to establish dialog between two users. All of them are decentralized though.
The routers do, though. Through BGP, AS's communicate location information to the routing infrastructure of other AS's. 15 years ago we saw the decline of "everybody knows everything" as the routing tables of core infrastructure simply became too unwieldy.
As the post says, with sufficiently slow servers it's impossible to maintain chronology plus monotonicity, and as it says, since chronology is really only important within a conversation, the best solution is to ensure each reply has an in-reply-to field (which tweets already have), then ensure that the original tweet is fetched before displaying the reply, and accept only approximately chronological ordering for "threads". But... that doesn't mean the UI has to change to look threaded, or that you should see an entire conversation if you're following the person who started it. That's a crazy leap. With such an algorithm it can still look exactly like Twitter and most people won't notice the difference.
As an alternative, by the way, since these posts are so short, you could simply include the entire thread with each reply! A few kilobytes won't kill any servers.
Also, one of the blog comments raises a good point: IRC has the same problem and it works fine.
As an alternative, by the way, since these posts are so short, you could simply include the entire thread with each reply! A few kilobytes won't kill any servers.
Also, one of the blog comments raises a good point: IRC has the same problem and it works fine.
Isn't that what RSS was? I could make a post, and have it syndicated to whoever wanted to listen to me.
RSS doesn't guarantee global ordering, and has very high latency (because of polling). Both of these can be overcome, but require a new protocol.
I guess I feel that ordering should be up to the User Agent. This way I can sort things multiple ways depending on how I'm feeling.
I also don't see the latency as an issue, but I'm not someone who needs to know exactly what everyone else is doing at all moments of the day.
I also don't see the latency as an issue, but I'm not someone who needs to know exactly what everyone else is doing at all moments of the day.
Usenet was federated and seemed to have these properties.
This is addressed at the bottom. I don't know if this is true but the problem seems to be, although the posts show up chronologically in each thread, the threads might be out of order with respect to each other.
Depending on where you were connecting from, there could be serious delays in usenet. Like, some servers synced once a day kind of delays.
It's important to note though that hardware muscle and bandwidth were both much, much, much more scarce and expensive back then.
Most email IMAP servers provide both Date Sent and Date Received properties for each message, allowing the client to sort by either. Even in active mailing list threads, I've found that it's not that common for messages to get too out of order.
Assuming federated social services keep track of Date Received, it'd probably be okay to just sort by that.
Assuming federated social services keep track of Date Received, it'd probably be okay to just sort by that.
your node can just wait until it’s received the latest content from every other node before displaying anything.
"Every other node" just means the nodes where the people you follow are hosted, not every node in the network. For most people, that would probably be a very small number.
"Every other node" just means the nodes where the people you follow are hosted, not every node in the network. For most people, that would probably be a very small number.
My hunch is that it's technically possible to go not just federated but radically distributed. However, there's more money to be made in centralization, creating defensible toll booths. And right now the sorts of developers and protocol/system architects who could make a radically distributed alternative are now fully overemployed doing other lucrative or beneficial things.
So it's a little harder technically, and lot less lucrative, to make a radically distributed alternative. And whatever the abuses of the centralized proprietors, they're still not changing those tradeoffs -- most users and even platform participants can still make-do under centralization.
A big tech bust freeing more talent to work on ideological (rather than pecuniary) projects, or enough heavy-handedness from the centralized proprietors, could change that balance.
So it's a little harder technically, and lot less lucrative, to make a radically distributed alternative. And whatever the abuses of the centralized proprietors, they're still not changing those tradeoffs -- most users and even platform participants can still make-do under centralization.
A big tech bust freeing more talent to work on ideological (rather than pecuniary) projects, or enough heavy-handedness from the centralized proprietors, could change that balance.
You're right. Gnutella was developed in 2000, eDonkey in 2000, Freenet in 2000, BitTorrent in 2001.
I think Twitter also has users distributed on different servers, making it effectively federated.
It hurts a little when the author mentions Usenet - and then doesn't realize that yes, of course it could trivially emulate twitter.
Regardless I don't find the notion of a federated twitter particularly interesting anyway. The future is P2P.
Regardless I don't find the notion of a federated twitter particularly interesting anyway. The future is P2P.
Personally, I'm willing to lose monotonicity. I mean, it's only Twitter. If I don't see every single message because I didn't scroll back far enough, I don't really care.
I doubt the single global ordering is as important as the author suggests. If nothing is in practice delayed for more than a short period, then either ordering-by-arrival or ordering-by-declared-time-with-'seen'-indicator both mostly work. It's whatever you get used to.
And I've seen all sorts of micro-failures in Twitter's provision of global ordering: gaps in my display timeline in one client but not others; tweets seeming to appear below the 'topmost' position when revisiting the stream; difficulty reloading recent history that was already local at one point.
A distributed/federated system might be a little fuzzier on some ordering behaviors... but make up for that in other dimensions.
And I've seen all sorts of micro-failures in Twitter's provision of global ordering: gaps in my display timeline in one client but not others; tweets seeming to appear below the 'topmost' position when revisiting the stream; difficulty reloading recent history that was already local at one point.
A distributed/federated system might be a little fuzzier on some ordering behaviors... but make up for that in other dimensions.
I think IRC does this type of mass node interconnection quite well.
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status.net already done.
identi.ca etc.
identi.ca etc.
"violating monotonicity means you can’t assume you’ve seen everything once you’ve read to the top of your timeline."
if that turns out to be such a problem,
1.) you can simply assume that everything fresher than 5 minutes is subject to change, so you ignore it until it's at least 5 minutes old.
2.) whatever site or app you're using could simply mark unread messages, and inform you of out-of-order messages.
if that turns out to be such a problem,
1.) you can simply assume that everything fresher than 5 minutes is subject to change, so you ignore it until it's at least 5 minutes old.
2.) whatever site or app you're using could simply mark unread messages, and inform you of out-of-order messages.
Unfortunately Jaiku was bought by google and they spent a long time with it offline only to come out as Google Buzz which didn't take off.
Many of the early twitter engineers like Blaine Cook and Alex Payne pushed hard for twitter to be more open and federated, but lost that argument and left or were pushed out. It's a business not a technology decision which makes twitter centralized.