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I expect that in a few years what was the real problem with RDBMS is going to be very clear, even if now it can look confusing enough and there are different al

I expect that in a few years what was the real problem with RDBMS is going to be very clear, even if now it can look confusing enough and there are different alternatives and it is very hard to meter the relative value of the different solutions proposed. I expect that in a few years antirez will study relational theory and conclude that he's been incrementally, unknowingly, implementing an RDBMS this whole time.

antirez 17y ago
Redis can be the most useless piece of code in the world but it is very hard looking at the command reference to state that Redia is going to be an rdbms in my humble opinion
- davidmathers 17y ago
  I'm not 100% sure, but it looks like redis might already have the low level building blocks of a relational dbms. The relational model is: relations + relational operators + boolean logic. A relation is just a special kind of set construction and redis has sets, so relations can be built. All of logic and operations can be built from either (not + and) or (not + or). You have SISMEMBER (not), SUNION (and), and SINTER (or). That might be enough.
  - kragen 17y ago
    You can't get select, project, or cartesian product out of ismember, union, and intersection. Also, union corresponds to and and intersection corresponds to or, not the other way around as your comment has it.
    - davidmathers 17y ago
      You can't get select, project, or cartesian product out of ismember, union, and intersection. Sorry, I didn't mention that redis has SADD and SREM for implementing projection. I'm not sure what you mean by select. You're right about product. I think that's what's missing. Also, union corresponds to and and intersection corresponds to or That's exactly what I said. We both got it backwards.
      - kragen 17y ago
        Haha! You're right. "Select" is the SPC-algebra operation which gives you the subset of a relation whose tuples satisfy some Boolean condition, e.g. firstname='bob'.
kragen 17y ago
I think that's totally unwarranted. He essentially pointed out that MongoDB is actually an RDBMS, and clearly explained how Redis is different, and why.
- davidmathers 17y ago
  There's nothing relational about MongoDB. At all. Relations are sets. MongoDB is setless.
  - antirez 17y ago
    David mine it's not a critique to MongoDB at all. It's just a matter of different models. In MongoDB objects are composed of fields with values, and this is very like tables, and you can perform queries that while are not written in SQL are actually very similar to SELECTs. Also you can set indexes into fields, that means, there is some kind of implicit structure to access the data. If you don't like it, I'll not tell the word "relational" since it is not very correct in this context, but this model is mathematically and algorithmically similar to what is inside the implementation of MySQL for instance. To state it more clearly, in this model, the access pattern is not already implicit in the way data is stored by the user. With Redis lists it's pretty obvious (and you can see in the doc the time complexity of all the operations), that if you use LPUSH against a list, then with LRANGE you can get the top 10 items in constant time regardless of the length of the list: this is because of the data model, Redis lists are already ordered because they are just linked lists, and so on. This is not to say Redis is better or MongoDB is better, it's just a different point of view, MongoDB implements a smart subset of the features provided by an RDBMS while Redis tries to take a different path where you select a data structure that is the best for the way you'll later retrieve those data.
    - davidmathers 17y ago
      This is not to say Redis is better or MongoDB is better, it's just a different point of view Sure. I didn't mean to imply any criticism, or imply that you were criticizing. I, personally, haven't figured out when/where to use a document database like Mongo or Couch, but I figure they must be a good fit for someone's use case or people wouldn't be making them. The thing that I have trouble with is that in every presentation or discussion I've seen of these alternative databases the people presenting them never seem to have an understanding of what a relational database is. And because the language in these presentations is always so obfuscated (to me) I'm never able to get a clear idea of what exactly they do and where they stand in relation to a relational DBMS (by which I mean the platonic ideal of a relational DBMS, not SQL). Redis is interesting to me because it's unlike the others. And because of the way it's unlike the others. It has data structures with operations. In other words it's a DBMS, or "structure server" in your terminology. At its core a relational DBMS is just a "structure server" with one kind of data structure, called a relation, and operations on that structure. And that's all it is really. Others probably disagree but I think even a query language is optional. The query language is just the UI. SQL confuses everything. A SQL DBMS is a relational DBMS (almost) plus a boatload of additional functionality. I see your point about how Mongo is like SQL because it has named values and queries, but it doesn't have relations or relational operators. In summary: Mongo may have some SQL like features, but they aren't relational features. The set features of Redis on the other hand are getting close to the building blocks of the core of an actual relational DBMS.
silentbicycle 17y ago
Which might not be a bad thing. I'd like to see something implement the relational model well but lose the cruft that got into the SQL standard. (Duplicated tuples? WTF?)

antirez 17y ago

Redis can be the most useless piece of code in the world but it is very hard looking at the command reference to state that Redia is going to be an rdbms in my humble opinion

davidmathers 17y ago
I'm not 100% sure, but it looks like redis might already have the low level building blocks of a relational dbms. The relational model is: relations + relational operators + boolean logic. A relation is just a special kind of set construction and redis has sets, so relations can be built. All of logic and operations can be built from either (not + and) or (not + or). You have SISMEMBER (not), SUNION (and), and SINTER (or). That might be enough.
- kragen 17y ago
  You can't get select, project, or cartesian product out of ismember, union, and intersection. Also, union corresponds to and and intersection corresponds to or, not the other way around as your comment has it.
  - davidmathers 17y ago
    You can't get select, project, or cartesian product out of ismember, union, and intersection. Sorry, I didn't mention that redis has SADD and SREM for implementing projection. I'm not sure what you mean by select. You're right about product. I think that's what's missing. Also, union corresponds to and and intersection corresponds to or That's exactly what I said. We both got it backwards.
    - kragen 17y ago
      Haha! You're right. "Select" is the SPC-algebra operation which gives you the subset of a relation whose tuples satisfy some Boolean condition, e.g. firstname='bob'.

kragen 17y ago

I think that's totally unwarranted. He essentially pointed out that MongoDB is actually an RDBMS, and clearly explained how Redis is different, and why.

davidmathers 17y ago
There's nothing relational about MongoDB. At all. Relations are sets. MongoDB is setless.
- antirez 17y ago
  David mine it's not a critique to MongoDB at all. It's just a matter of different models. In MongoDB objects are composed of fields with values, and this is very like tables, and you can perform queries that while are not written in SQL are actually very similar to SELECTs. Also you can set indexes into fields, that means, there is some kind of implicit structure to access the data. If you don't like it, I'll not tell the word "relational" since it is not very correct in this context, but this model is mathematically and algorithmically similar to what is inside the implementation of MySQL for instance. To state it more clearly, in this model, the access pattern is not already implicit in the way data is stored by the user. With Redis lists it's pretty obvious (and you can see in the doc the time complexity of all the operations), that if you use LPUSH against a list, then with LRANGE you can get the top 10 items in constant time regardless of the length of the list: this is because of the data model, Redis lists are already ordered because they are just linked lists, and so on. This is not to say Redis is better or MongoDB is better, it's just a different point of view, MongoDB implements a smart subset of the features provided by an RDBMS while Redis tries to take a different path where you select a data structure that is the best for the way you'll later retrieve those data.
  - davidmathers 17y ago
    This is not to say Redis is better or MongoDB is better, it's just a different point of view Sure. I didn't mean to imply any criticism, or imply that you were criticizing. I, personally, haven't figured out when/where to use a document database like Mongo or Couch, but I figure they must be a good fit for someone's use case or people wouldn't be making them. The thing that I have trouble with is that in every presentation or discussion I've seen of these alternative databases the people presenting them never seem to have an understanding of what a relational database is. And because the language in these presentations is always so obfuscated (to me) I'm never able to get a clear idea of what exactly they do and where they stand in relation to a relational DBMS (by which I mean the platonic ideal of a relational DBMS, not SQL). Redis is interesting to me because it's unlike the others. And because of the way it's unlike the others. It has data structures with operations. In other words it's a DBMS, or "structure server" in your terminology. At its core a relational DBMS is just a "structure server" with one kind of data structure, called a relation, and operations on that structure. And that's all it is really. Others probably disagree but I think even a query language is optional. The query language is just the UI. SQL confuses everything. A SQL DBMS is a relational DBMS (almost) plus a boatload of additional functionality. I see your point about how Mongo is like SQL because it has named values and queries, but it doesn't have relations or relational operators. In summary: Mongo may have some SQL like features, but they aren't relational features. The set features of Redis on the other hand are getting close to the building blocks of the core of an actual relational DBMS.

silentbicycle 17y ago

Which might not be a bad thing. I'd like to see something implement the relational model well but lose the cruft that got into the SQL standard. (Duplicated tuples? WTF?)