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rqlite[1] creator here. This offering is completely new to me. Welcome to the party, that's what I say. I started doing what they are doing about 10 years ago.

rqlite[1] creator here. This offering is completely new to me. Welcome to the party, that's what I say. I started doing what they are doing about 10 years ago. :-) https://www.philipotoole.com/9-years-of-open-source-database-development-the-design-docs/ https://www.philipotoole.com/9-years-of-open-source-database... https://www.philipotoole.com/replicating-sqlite-using-raft-consensus/ https://www.philipotoole.com/replicating-sqlite-using-raft-c... https://www.philipotoole.com/rqlite-v3-0-1-globally-replicating-sqlite/ https://www.philipotoole.com/rqlite-v3-0-1-globally-replicat... The post makes a fairly big point of the shortcomings of statement-based replication (like what rqlite does). What they state is correct -- non-deterministic SQL will be a problem, but it's not a difficult problem to solve. Just parse and rewrite the SQL statement before sending it to Raft. It's exactly what rqlite does[2] (though there is more to do). However they claim that there are two concerns with this approach. >This solution introduces a runtime delay because each SQL statement must be parsed and analyzed. The delay is insignificant compared with the delay introduced by Raft consensus. This is not a valid concern. I'm surprised they even mentioned it. >More importantly, it increases the difficulty of staying up-to-date with the new versions of the underline SQL engine (SQLite in this specific case) because the custom parser must be updated each time a new SQL function/feature is introduced. Theoretically somewhat true, but not true in practice. Any competent programmer can update any parsing code in a matter of hours. Also just because a new feature is introduced does not mean that the parser needs to be rewritten. That's because SQLite will not introduce breaking changes into their SQL specification. Any parser needs to be updated only if you want to support any new, non-deterministic feature. [1] https://rqlite.io https://rqlite.io [2] https://rqlite.io/docs/api/non-deterministic/ https://rqlite.io/docs/api/non-deterministic/

justinclift 4y ago
With rqlite, the docs indicate that a single node setup should run ok. Is that supposed to still apply when a small cluster (eg three nodes) is reduced to a single node? eg during node failures, maintenance, node failures during maintenance ;), etc. When I was trying rqlite last week - eg prototyping a new SQLite "cloud" offering for DBHub.io - a remaining single node would consistently refuse to elect itself as the leader. Using default settings for everything. Tried it out several times, though I didn't give it more than a minute or two to get itself happy. Anyway, had to go with an initial non-RAFT approach for the prototype, but will likely investigate rqlite again in the future if I was just doing something dumb / fixable with tweaking. :)
- otoolep 4y ago
  A single node should work perfectly fine when it's the only node in the cluster i.e. you're running a single-node cluster. If you couldn't bring up a single node from scratch, you're doing something wrong. :-) Show me your launch command, or join the rqlite Slack channel for help (https://www.philipotoole.com/join-rqlite-slack https://www.philipotoole.com/join-rqlite-slack) However if you create a 3-node cluster (or add 2 nodes to an existing single-node cluster) then at least a quorum of nodes (N/2 +1) must be up and running for the cluster to be available. That's the way Raft works -- Cockroach, etcd, Consul -- all of them will work the same way. So in your case a 3-node cluster with 2 nodes subsequently going down (or deliberately taken offline) is a cluster which is offline. There is extensive documentation available on clustering, which you should review: https://rqlite.io/docs/clustering/ https://rqlite.io/docs/clustering/
  - justinclift 4y ago
    Oh, the "getting a single node cluster" up and running was easy, as you said. It's just it wasn't clear from the initial docs I saw that a 3 -> 1 cluster would be considered any differently. Clearly, an error on my part. :) I'll circle back to rqlite in a while, after I get this existing prototype code rolled out and see what people make of it. Hopefully it turns out to be useful for people.
    - otoolep 4y ago
      Yeah, going from 3->1 simply by taking down nodes won't work -- that's breaking quorum. If you really want to do this, you can explicitly override the configuration stored in Raft. Check out these directions: https://rqlite.io/docs/clustering/general-guidelines/#recovering-a-cluster-that-has-permanently-lost-quorum https://rqlite.io/docs/clustering/general-guidelines/#recove... While this talks about "dealing with failure" using the config file described above basically allows you to force the cluster into any configuration you want (including a single-node cluster).
      - otoolep 4y ago
noman-land 4y ago
I learned about rqlite just the other day and plan on using it in my next project. Thanks for making it!
marcobambini 4y ago
It seems to me that all date and time functions and default values like CURRENT_TIMESTAMP, CURRENT_TIME, and CURRENT_DATE are all missed cases. The problem is not solved with a parser, and this approach could lead to severe issues. Even more, when date and time default values are used in CREATE TABLE statements it seems very difficult to me to rewrite an INSERT statement that does not include that columns.

justinclift 4y ago

With rqlite, the docs indicate that a single node setup should run ok. Is that supposed to still apply when a small cluster (eg three nodes) is reduced to a single node? eg during node failures, maintenance, node failures during maintenance ;), etc. When I was trying rqlite last week - eg prototyping a new SQLite "cloud" offering for DBHub.io - a remaining single node would consistently refuse to elect itself as the leader. Using default settings for everything. Tried it out several times, though I didn't give it more than a minute or two to get itself happy. Anyway, had to go with an initial non-RAFT approach for the prototype, but will likely investigate rqlite again in the future if I was just doing something dumb / fixable with tweaking. :)

otoolep 4y ago
A single node should work perfectly fine when it's the only node in the cluster i.e. you're running a single-node cluster. If you couldn't bring up a single node from scratch, you're doing something wrong. :-) Show me your launch command, or join the rqlite Slack channel for help (https://www.philipotoole.com/join-rqlite-slack https://www.philipotoole.com/join-rqlite-slack) However if you create a 3-node cluster (or add 2 nodes to an existing single-node cluster) then at least a quorum of nodes (N/2 +1) must be up and running for the cluster to be available. That's the way Raft works -- Cockroach, etcd, Consul -- all of them will work the same way. So in your case a 3-node cluster with 2 nodes subsequently going down (or deliberately taken offline) is a cluster which is offline. There is extensive documentation available on clustering, which you should review: https://rqlite.io/docs/clustering/ https://rqlite.io/docs/clustering/
- justinclift 4y ago
  Oh, the "getting a single node cluster" up and running was easy, as you said. It's just it wasn't clear from the initial docs I saw that a 3 -> 1 cluster would be considered any differently. Clearly, an error on my part. :) I'll circle back to rqlite in a while, after I get this existing prototype code rolled out and see what people make of it. Hopefully it turns out to be useful for people.
  - otoolep 4y ago
    Yeah, going from 3->1 simply by taking down nodes won't work -- that's breaking quorum. If you really want to do this, you can explicitly override the configuration stored in Raft. Check out these directions: https://rqlite.io/docs/clustering/general-guidelines/#recovering-a-cluster-that-has-permanently-lost-quorum https://rqlite.io/docs/clustering/general-guidelines/#recove... While this talks about "dealing with failure" using the config file described above basically allows you to force the cluster into any configuration you want (including a single-node cluster).
    - otoolep 4y ago

noman-land 4y ago

I learned about rqlite just the other day and plan on using it in my next project. Thanks for making it!

marcobambini 4y ago

It seems to me that all date and time functions and default values like CURRENT_TIMESTAMP, CURRENT_TIME, and CURRENT_DATE are all missed cases. The problem is not solved with a parser, and this approach could lead to severe issues. Even more, when date and time default values are used in CREATE TABLE statements it seems very difficult to me to rewrite an INSERT statement that does not include that columns.