Yes you are correct. I am currently using kind of the same eventstore implementation in postgres for a SaaS app and the event rate is really low. However migrating the data to another system could be painful and you want to make the best decisions as early as possible but keeping the infra manageable without using many different systems. My worries for postgres are mostly about the table size. A rate of 1 event per second already produced 32 million of events per year. And after a year or two, you still want a decent performance for fetching a event stream or inserting an event
The nice thing about event sourcing is that events are the source of truth and they are pretty portable. We have copies of the system for multiple environments as I'm sure you do. So it would not be too much of a stretch to work out the integration details with a different solution, spin up a new system with it, save the existing events onto that copy, and validate it.
32 million rows is easy for postgres as far as just storage and insertion perf. One of our products is getting close to a million events after 6 years and it still runs lightly on micro instances. So I have lots of scale-up room before I need to reevaluate. That one used full consistency, so the read models are in the same db and there is write amplification. I used different schemas per tenant so it's not one set of indexes. If that does make a difference, the same could be accomplished with table partitioning.
The length of a stream (and therefore replay time) is more in the design camp than the perf camp. I've been meaning to make a post summarizing things I've learned and rules of thumb I use for event stream design. For example I will use unbounded streams for repeated processes. Like a yearly audit. But I don't replay the whole thing. I replay from the last completed audit. So replay sees a bounded number of events every time. And perf doesn't significantly change with years of history.
I will check that implementation out and see what I can learn. Thanks for linking it! :)
I only looked at the table structures. It looks like it's meant to be eventstore.com on postgres. Interesting idea.
One of things I didn't mention with scaling limits to postgres is connection limits. Each connection eats non-trivial amounts of server resources. Our AWS t2.micro instances can handle about 85 before it can't make new ones. (Ask me how I know.) But resources allocated to sessions are resources not allocated to running SQL. So we want to stay well below the limit. This is why things like Pgbouncer exist.
I want to explore creating my own event store service that will accept ES commands and use SignalR or WebSockets for listeners on top of my postgres ES. It can maintain its own limited number of connections to give the db as much resources as possible. And assign Positions from mem to alleviate that bottleneck. It can use opportunistic batching for yet more perf. Practically though, this creates many new downsides. An extra network hop (+latency). New failure modes and recovery models. Pub/sub handling. This is all potentially fun stuff I might like to do for my own learning. But when approaching limits of the original solution, for work I'd be evaluating eventstore.com instead since they solved most of these problems already. And it's high availability and free to use. I'm sure it has its own issues / workarounds, but probably so would my service. :)
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Yes you are correct. I am currently using kind of the same eventstore implementation in postgres for a SaaS app and the event rate is really low. However migrating the data to another system could be painful and you want to make the best decisions as early as possible but keeping the infra manageable without using many different systems. My worries for postgres are mostly about the table size. A rate of 1 event per second already produced 32 million of events per year. And after a year or two, you still want a decent performance for fetching a event stream or inserting an event
I also found another eventstore implementation for postgres, used with elixir: github.com/commanded/eventstore . They use a different table structure, as can be found here: github.com/commanded/eventstore/bl...
The nice thing about event sourcing is that events are the source of truth and they are pretty portable. We have copies of the system for multiple environments as I'm sure you do. So it would not be too much of a stretch to work out the integration details with a different solution, spin up a new system with it, save the existing events onto that copy, and validate it.
32 million rows is easy for postgres as far as just storage and insertion perf. One of our products is getting close to a million events after 6 years and it still runs lightly on micro instances. So I have lots of scale-up room before I need to reevaluate. That one used full consistency, so the read models are in the same db and there is write amplification. I used different schemas per tenant so it's not one set of indexes. If that does make a difference, the same could be accomplished with table partitioning.
The length of a stream (and therefore replay time) is more in the design camp than the perf camp. I've been meaning to make a post summarizing things I've learned and rules of thumb I use for event stream design. For example I will use unbounded streams for repeated processes. Like a yearly audit. But I don't replay the whole thing. I replay from the last completed audit. So replay sees a bounded number of events every time. And perf doesn't significantly change with years of history.
I will check that implementation out and see what I can learn. Thanks for linking it! :)
I only looked at the table structures. It looks like it's meant to be eventstore.com on postgres. Interesting idea.
One of things I didn't mention with scaling limits to postgres is connection limits. Each connection eats non-trivial amounts of server resources. Our AWS t2.micro instances can handle about 85 before it can't make new ones. (Ask me how I know.) But resources allocated to sessions are resources not allocated to running SQL. So we want to stay well below the limit. This is why things like Pgbouncer exist.
I want to explore creating my own event store service that will accept ES commands and use SignalR or WebSockets for listeners on top of my postgres ES. It can maintain its own limited number of connections to give the db as much resources as possible. And assign Positions from mem to alleviate that bottleneck. It can use opportunistic batching for yet more perf. Practically though, this creates many new downsides. An extra network hop (+latency). New failure modes and recovery models. Pub/sub handling. This is all potentially fun stuff I might like to do for my own learning. But when approaching limits of the original solution, for work I'd be evaluating eventstore.com instead since they solved most of these problems already. And it's high availability and free to use. I'm sure it has its own issues / workarounds, but probably so would my service. :)