5 ms·

Everything obviously has trade offs, no choice is perfect in everyway. For me the pros of having data as an immutable stream of events (eventsourcing) is that

Everything obviously has trade offs, no choice is perfect in everyway. For me the pros of having data as an immutable stream of events (eventsourcing) is that you get migrations and data modeling for free - You don't have to deal with having to design the "perfect" data model in advance (or worry about schema/data migrations later on) and you can get caching as first level data rather as derived from another store.

eloff 12y ago
It has it's advantages to be sure, I really like eventsourcing. For some kinds of projects it's the obvious way to go. Finance seems like a killer application, because of the way the entire audit trail is stored, and the system can often be rebuilt to a valid state upon finding and correcting a production bug.
- whatthemick 12y ago
  For anything that critically needs an audit log it's a pretty obvious choice (atleast compared to when people try to implement audit logs in a RDBMS). I think it might also have a great deal of merit in prototyping applications quickly - Having the option to do just-in-time/memory projections while later switching to "real" storage seems really ideal to me if i'm just building something to validate it would like to defer those type of tech decisions.
sitkack 12y ago
Actually @eloff and the OP are arguing past each other. Both are wrong in different ways. > Databases are global, shared, mutable state. That’s the way it has been since the 1960s, and no amount of NoSQL has changed that. However, most self-respecting developers have got rid of mutable global variables in their code long ago. So why do we tolerate databases as they are? This isn't true. Databases _can_ be those things, but that isn't the definition of a database. Most of the databases I have worked and created do not use update or delete except to archive old data that is no longer in the working set. And mutability isn't always faster. Most of the time when people are championing mutability, it is because it is the most expedient (esp with their mental model), not because from a whole system standpoint it is actually faster. They trot out a microbenchmark that proves their point while ignoring use cases like retrieving old state or auditing the transaction history.
- eloff 12y ago
  You'll have to go into detail. Mutable data structures mop the floor with immutable ones, synchronization issues aside. What's actually better depends on the specific case in question, but mutable data structures have a superset of the techniques available to immutable ones, and that's never a disadvantage. It, might, however lead you to use a poor design that falls down under contention.
  - sitkack 12y ago
    Mutability has to put into context of the whole system, not just a narrowly focused benchmark. We can no longer put synchronization issues aside, that just isn't possible anymore. Correctness (coherency and data races) both on a micro level and macro are more important than raw mutation rates. While there are times when mutation is the answer, it has to thought about carefully.
    - eloff 12y ago
      Correctness is very important. But being correct and faster is better. A lot of the techniques I use to accomplish that start to look similar to immutable. Copy on write is the cornerstone of good lock-free algorithms as well as immutable data structures. However, not being religious about mutability has tangible performance benefits - depending on the details, as always.
      - sitkack 12y ago
        Yes, but that stuff is hard and error prone. Immutability is easier (safer, more correct) on the whole. I think both Rust and Clojure take a good stance on mutation. Only for anecdotal evidence, my ad-hoc immutable (lots of copying) ETLs performed better than the mutation happy ones. The GC was able to throw stuff away faster, the code was cleaner, kept only what it needed. The gaussian circle of confusion was smaller.
        eloff 12y ago

eloff 12y ago

It has it's advantages to be sure, I really like eventsourcing. For some kinds of projects it's the obvious way to go. Finance seems like a killer application, because of the way the entire audit trail is stored, and the system can often be rebuilt to a valid state upon finding and correcting a production bug.

whatthemick 12y ago
For anything that critically needs an audit log it's a pretty obvious choice (atleast compared to when people try to implement audit logs in a RDBMS). I think it might also have a great deal of merit in prototyping applications quickly - Having the option to do just-in-time/memory projections while later switching to "real" storage seems really ideal to me if i'm just building something to validate it would like to defer those type of tech decisions.

sitkack 12y ago

Actually @eloff and the OP are arguing past each other. Both are wrong in different ways. > Databases are global, shared, mutable state. That’s the way it has been since the 1960s, and no amount of NoSQL has changed that. However, most self-respecting developers have got rid of mutable global variables in their code long ago. So why do we tolerate databases as they are? This isn't true. Databases _can_ be those things, but that isn't the definition of a database. Most of the databases I have worked and created do not use update or delete except to archive old data that is no longer in the working set. And mutability isn't always faster. Most of the time when people are championing mutability, it is because it is the most expedient (esp with their mental model), not because from a whole system standpoint it is actually faster. They trot out a microbenchmark that proves their point while ignoring use cases like retrieving old state or auditing the transaction history.

eloff 12y ago
You'll have to go into detail. Mutable data structures mop the floor with immutable ones, synchronization issues aside. What's actually better depends on the specific case in question, but mutable data structures have a superset of the techniques available to immutable ones, and that's never a disadvantage. It, might, however lead you to use a poor design that falls down under contention.
- sitkack 12y ago
  Mutability has to put into context of the whole system, not just a narrowly focused benchmark. We can no longer put synchronization issues aside, that just isn't possible anymore. Correctness (coherency and data races) both on a micro level and macro are more important than raw mutation rates. While there are times when mutation is the answer, it has to thought about carefully.
  - eloff 12y ago
    Correctness is very important. But being correct and faster is better. A lot of the techniques I use to accomplish that start to look similar to immutable. Copy on write is the cornerstone of good lock-free algorithms as well as immutable data structures. However, not being religious about mutability has tangible performance benefits - depending on the details, as always.
    - sitkack 12y ago
      Yes, but that stuff is hard and error prone. Immutability is easier (safer, more correct) on the whole. I think both Rust and Clojure take a good stance on mutation. Only for anecdotal evidence, my ad-hoc immutable (lots of copying) ETLs performed better than the mutation happy ones. The GC was able to throw stuff away faster, the code was cleaner, kept only what it needed. The gaussian circle of confusion was smaller.
      - eloff 12y ago