Consider adding router executor back to Citus Query Processing section

[samay-sharma]

In Citus 5.0, we used to have a section on Router Executor in our Citus Query Processing section. Currently, the page doesn't have that section since we removed it with 5.1. However, since the multi-tenant use case uses it heavily, we should probably re-add the section.

[ozgune]

@samay-sharma, @begriffs, @sumedhpathak -- I wanted to add a note to this issue.

We talked about this issue in our product planning session yesterday. We have three sections in our docs, where we talk about real-time and task-tracker executors:

• Citus Query Processing
• Distributed Query Performance Tuning
• Citus Task Executor Type Config (I'm not sure if we'd like to mention router planner and executor here.)

One challenge is how much we'd like to communicate router planner / executor to users. Do we for example want to go into router planner? Ideally, the simpler we can communicate this executor type's benefits to users, the better.

[onderkalaci]

+1 for this.

I think query processing documentation is far behind the current product, missing the multi-tenant model (at all?).

For instance: The planning process for key-value lookups on the distribution column or modification queries is slightly different as they hit exactly one shard. is misleading. We probably should not mention key-value lookups, which connotates other systems and is primitive than what router planner can handle. Similarly, single shard is a subset of router planner's capability.

(I remember @samay-sharma writing this documentation years back in Istanbul. Seems its time to update it 😄 )

[begriffs]

We now have bigger sections for each executor in https://docs.citusdata.com/en/v7.3/performance/query_processing.html#distributed-query-executor

Although that "key-value" sentence still survives.

Should we close this issue?