4 ms·

> wait until all its key-value pairs have timed out and then just shut it down you can do it that way but it often winds up making the server's shutdown depend

by zemo 7y ago

> wait until all its key-value pairs have timed out and then just shut it down you can do it that way but it often winds up making the server's shutdown dependent on a client behavior. For example, the liveness of a key is determined by the client in most applications, not the server. Any sort of naive TTL system where a read on a key extends its lifetime means that the server cannot shut down without permission from the clients, because the client can just keep reading the same key over and over, extending its lifetime until the client shuts down. I have a system that works this way now, I'm working on removing that behavior. When I want to take a server offline, I have no idea if it will take ten minutes or four hours to drain. It's very annoying. > have each client send everything to both of the session state servers generally a client would write to just one server (server A), and that server would write to the other server (server B). If server A applies the change locally and then confirms it with the client, then syncs the change to server B independently of the client request, that's asynchronous replication. If server A waits until server B has applied the change locally before confirming the write with the client, that's synchronous replication. If the client can only send writes to one of the servers, but can send reads to either server, that's master-replica replication. The easiest thing to reason about is synchronous master-replica systems: client sends a request to A, A applies it to A's storage, A sends it to B, B applies it to B's storage, B confirms it with A, A confirms it with the client. If a client can send a write to either server, that's master-master replication. Master-master replication is harder to implement; what if two different clients write the same key on two different servers at the same time? A conflict arises. Concurrency issues are unavoidable in web systems. Uncoordinated users are using the system simultaneously; "everybody wait in line" is not a realistic option in practice. > What do people do about that, say, at high end sites? that varies pretty widely. Depends a lot on what you're building, how much money you have, how much time you have, how many users you have, how many engineers you have, how easy it is for you to hire, what skills your current engineering team has, what clients will be accessing the data, etc. The permutations of concerns are innumerable. Lots of people buy hosted redis from redislabs.com or AWS Elasticache because they are either unwilling or unable to run a redis server themselves. That's a great solution for most people most of the time; it works great for a lot of use cases, it's relatively inexpensive, and the providers give you useful tools that you would otherwise have to build yourself. > Maybe I should think about implementing more. Are you selling a key-value store? What is your startup? Maybe you should think about implementing less, and focusing on building the things that actually matter to users. Key-value stores are nice engineering problems, but they're implementation details: users don't know about and don't care about their existence, and their existence does not drive revenue. And that's why most people just buy hosted redis, download a redis client library, and call it a day. It's not technically the best solution, but it's often times the most economical solution.

graycat 7y ago
Many thanks. A keeper. Of course, you are fully correct about waiting until all the users have timed out. Even if I set the time out to 1 hour of inactivity, a user could do something each 10 minutes for days, as you mentioned. The only things I would consider adding to my key-value Web session state store would be some little system management commands/queries. I have some now. They are dirt simple to implement. We're talking no more than an easy day. I wouldn't be trying to implement much. I'm learning: I time I'll want a graceful, fast, high performance, and reliable way to move key-value pairs from one server to another one. If Redis or some such has that, then I won't program it -- buy, not build. Early on I have been intending to do nothing special about hardware redundancy for on-line reliability. I suspect I can get the equipment and software needed for the on-line work to run fine for weeks at a time. That should be enough for alpha test, beta test, version 1.0, and some ad revenue. Then I'll take some simple approaches to hardware redundancy and keep growing. Maybe a Cisco box between the Internet and my Web servers could help bring Web servers on/off line. And, sure, some uninterruptible power supply boxes for the computers, network equipment, lights, etc.! > Are you selling a key-value store? Heck no! > What is your startup? Might as well say -- close enough to the alpha test which I intend to announce here: It's a new and very different Web content search engine for the, my guess, 2/3rds of the content on the Web, searches people want to do, and results they want to find currently served at best poorly. It's all safe for work, families, and children, uses no cookies, has no logins, and likely meets the EU GDPR standards. It makes no use of old data specific to a user: That is, if two users give the same inputs on the same day, then they will get the same results (assuming I do system updates at night!). They may not get the same ads. There is no use of key words. It gets new data via an interactive, iterative dialog. In this way, the results are highly personalized. Users get to drill own, focus in, filter out, zoom in. Actually it's more about discovery and recommendation than search. Or, roughly key word search requires a user looking for Web content (i) to know what they want, (ii) to know that it exists, and (iii) to have key words that accurately enough characterize that content. I suspect that now often what the users are getting is some "Top 40" version based on popularity. When a user has (i)-(iii), key words can work well. If what they want is really popular, then they can do a sloppy key word search and still get what they want. But IMHO that covers only about 1/3rd of the content, searches, and results of interest. Some people at Battelle knew some such things long ago. Key words are especially poor on still images, video clips, and recorded music. All that aside, in the 2/3rds, what a user really wants is the content with the meaning they have in mind. Getting at meaning has been challenging: Key word search has a tough time getting at meaning even for content based on text. To be clear, in the 2/3rds, the user is looking for something they have never seen before and don't even know exists. So, they need recommendation and discovery of content with the meaning they want. The key to the whole thing is some applied math I derived, complete with theorems and proofs, to process the data. The applied math is based on some advanced pure math prerequisites. The data manipulations are not heuristic, data science, machine learning, neural anything, or artificial intelligence and, really, not in computer science. Instead, the core is some math -- of course the users won't be aware of anything mathematical. I had the code running on Windows XP, but then that motherboard quit. I didn't lose any code. Now I'm bringing up the code, for an alpha test, on the box I plugged together, an AMD FX-8350 at 4.0 GHz with Windows 7 64 bit Professional. The code is about 24,000 programming language statements in about 100,000 lines of typing. Yup, it's all in VB.NET -- the language looked fine to me. Likely in time I should convert to some version of Windows Server. Now, if I can get simple file sharing not to make a mess out of archive bits, it will help.

by zemo 7y ago

graycat 7y ago

Many thanks. A keeper. Of course, you are fully correct about waiting until all the users have timed out. Even if I set the time out to 1 hour of inactivity, a user could do something each 10 minutes for days, as you mentioned. The only things I would consider adding to my key-value Web session state store would be some little system management commands/queries. I have some now. They are dirt simple to implement. We're talking no more than an easy day. I wouldn't be trying to implement much. I'm learning: I time I'll want a graceful, fast, high performance, and reliable way to move key-value pairs from one server to another one. If Redis or some such has that, then I won't program it -- buy, not build. Early on I have been intending to do nothing special about hardware redundancy for on-line reliability. I suspect I can get the equipment and software needed for the on-line work to run fine for weeks at a time. That should be enough for alpha test, beta test, version 1.0, and some ad revenue. Then I'll take some simple approaches to hardware redundancy and keep growing. Maybe a Cisco box between the Internet and my Web servers could help bring Web servers on/off line. And, sure, some uninterruptible power supply boxes for the computers, network equipment, lights, etc.! > Are you selling a key-value store? Heck no! > What is your startup? Might as well say -- close enough to the alpha test which I intend to announce here: It's a new and very different Web content search engine for the, my guess, 2/3rds of the content on the Web, searches people want to do, and results they want to find currently served at best poorly. It's all safe for work, families, and children, uses no cookies, has no logins, and likely meets the EU GDPR standards. It makes no use of old data specific to a user: That is, if two users give the same inputs on the same day, then they will get the same results (assuming I do system updates at night!). They may not get the same ads. There is no use of key words. It gets new data via an interactive, iterative dialog. In this way, the results are highly personalized. Users get to drill own, focus in, filter out, zoom in. Actually it's more about discovery and recommendation than search. Or, roughly key word search requires a user looking for Web content (i) to know what they want, (ii) to know that it exists, and (iii) to have key words that accurately enough characterize that content. I suspect that now often what the users are getting is some "Top 40" version based on popularity. When a user has (i)-(iii), key words can work well. If what they want is really popular, then they can do a sloppy key word search and still get what they want. But IMHO that covers only about 1/3rd of the content, searches, and results of interest. Some people at Battelle knew some such things long ago. Key words are especially poor on still images, video clips, and recorded music. All that aside, in the 2/3rds, what a user really wants is the content with the meaning they have in mind. Getting at meaning has been challenging: Key word search has a tough time getting at meaning even for content based on text. To be clear, in the 2/3rds, the user is looking for something they have never seen before and don't even know exists. So, they need recommendation and discovery of content with the meaning they want. The key to the whole thing is some applied math I derived, complete with theorems and proofs, to process the data. The applied math is based on some advanced pure math prerequisites. The data manipulations are not heuristic, data science, machine learning, neural anything, or artificial intelligence and, really, not in computer science. Instead, the core is some math -- of course the users won't be aware of anything mathematical. I had the code running on Windows XP, but then that motherboard quit. I didn't lose any code. Now I'm bringing up the code, for an alpha test, on the box I plugged together, an AMD FX-8350 at 4.0 GHz with Windows 7 64 bit Professional. The code is about 24,000 programming language statements in about 100,000 lines of typing. Yup, it's all in VB.NET -- the language looked fine to me. Likely in time I should convert to some version of Windows Server. Now, if I can get simple file sharing not to make a mess out of archive bits, it will help.