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Hey Alex, I explored potentially using Calcite when we initiated this project. The syntax is very similar because both are an SQL dialect. Some differences are

Hey Alex, I explored potentially using Calcite when we initiated this project. The syntax is very similar because both are an SQL dialect. Some differences are that MQL largely targets unstructured data (there is no schema for the streams it operates on - they're just streams of JSON blobs). In addition to that one of the goals of MQL was to have different compiler backends which allows different call sites to operate on different levels. For example the code that runs in our API/proxy/other large services will look at an entire query and only evaluate the WHERE / SAMPLE clauses expecting something down the stream to complete the query. Conversely the client side is a full SQL -> RxJava implementation for the data stream. I can explain more of how this works if there is interest -- it allows us to only egress data that is actively used in queries so devs can log every request and only pay the cost of those for which they are querying.) Doing our own implementation also allows us more customization, and to compile to a NodeJS backend as well which is a critical ingestion point for our operational data. We support everything on the linked page except hopping windows, subqueries, and DML (MQL is query only, we assume no structure which was true of the streams before we ever wrote a query language for it). Of course we have to implement a lot more of this ourselves which is pretty in line with Netflix's Freedom and Responsibility. We had the freedom to implement our own query language but have the responsibility to maintain it (Calcite would have been sacrificing some freedom to avoid responsibility.)

alextheparrot 8y ago
Thanks for the detailed answer - as you likely already know many projects have taken the approach you detailed in your past paragraph, it makes sense if your goal is more freedom for sure. I am wondering how you do client side data egress filtering - does each event need to get materialized, assessed for certain fields or structure, and then sent once for each outgoing stream on your sender? Seems like a good strategy for reducing network bandwidth, but it might reduce your throughout moderately (Due to serialization and analysis costs) or cause hotspots (If you have a distributed stream that is partioned in a particular way)? These are normally problems each consumer individually faces, where now it compounds where the producer does that work for each of the N readers. I appreciate the idea a lot, just wondering if you’ve had any issues making it scale nicely for highly subscribed streams.
- diab0lic 8y ago
  The events are already materialized in memory as part of whatever is recording them, thankfully. The MQL that runs in the services checks the WHERE clause of every query running and then projects a superset of all the fields necessary for every part of the query for all matching queries (including other parts that the server won't be processing: group by, order by, having, etc...). It then tags the event with all of the matching queries. This way we only need to egress a single event. What happens next requires a lot more context about Mantis, which is a reactive stream processor. The data is egressed from the service to what is referred to as a source job in Mantis... it is the source job's responsibility to multiplex this data to any of the consuming jobs. Jobs can be subscribed to one another so this is a natural fit for Mantis. As for scaling everything is round robin after it leaves the service and enters Mantis but obviously busier services will pay more cost because they're processing more events. Regular expressions in WHERE clauses has been a pain point for scale, and absurdly heavy queries such as `SELECT * FROM STREAM` result in data dropping as most single machine consumers can't keep up with the large streams. We have different methods of providing different delivery semantics but in the base case we're at most once and will drop data if the client can't keep up. We have some streams that exceed 1 million RPS at certain times of the day, and last we checked the system moves around 2 trillion events per day so we've managed to scale it to the needs of the company pretty well. It has been a while since I performance tested it, but it's always been a goal to have it push as close as possible to saturating the gigabit connection on the boxes on which it runs.

alextheparrot 8y ago

Thanks for the detailed answer - as you likely already know many projects have taken the approach you detailed in your past paragraph, it makes sense if your goal is more freedom for sure. I am wondering how you do client side data egress filtering - does each event need to get materialized, assessed for certain fields or structure, and then sent once for each outgoing stream on your sender? Seems like a good strategy for reducing network bandwidth, but it might reduce your throughout moderately (Due to serialization and analysis costs) or cause hotspots (If you have a distributed stream that is partioned in a particular way)? These are normally problems each consumer individually faces, where now it compounds where the producer does that work for each of the N readers. I appreciate the idea a lot, just wondering if you’ve had any issues making it scale nicely for highly subscribed streams.

diab0lic 8y ago
The events are already materialized in memory as part of whatever is recording them, thankfully. The MQL that runs in the services checks the WHERE clause of every query running and then projects a superset of all the fields necessary for every part of the query for all matching queries (including other parts that the server won't be processing: group by, order by, having, etc...). It then tags the event with all of the matching queries. This way we only need to egress a single event. What happens next requires a lot more context about Mantis, which is a reactive stream processor. The data is egressed from the service to what is referred to as a source job in Mantis... it is the source job's responsibility to multiplex this data to any of the consuming jobs. Jobs can be subscribed to one another so this is a natural fit for Mantis. As for scaling everything is round robin after it leaves the service and enters Mantis but obviously busier services will pay more cost because they're processing more events. Regular expressions in WHERE clauses has been a pain point for scale, and absurdly heavy queries such as `SELECT * FROM STREAM` result in data dropping as most single machine consumers can't keep up with the large streams. We have different methods of providing different delivery semantics but in the base case we're at most once and will drop data if the client can't keep up. We have some streams that exceed 1 million RPS at certain times of the day, and last we checked the system moves around 2 trillion events per day so we've managed to scale it to the needs of the company pretty well. It has been a while since I performance tested it, but it's always been a goal to have it push as close as possible to saturating the gigabit connection on the boxes on which it runs.