feat: explain a query and output a Graphviz representation of the query plan

[lmatz]

In the case of a large complex query, a visualized representation can be clearer to diagnose problems, e.g. easier to know which two upstream are joined together if they are separated far away in the output of explain <SQL>.

https://github.com/risingwavelabs/risingwave/blob/main/src/frontend/src/scheduler/distributed/query.rs#L293-L294 output a task-level graphviz representation for debugging usage.

We can enable a query plan representation via the command explain (graphviz) <SQL>.

[kwannoel]

Related: #14168

[kwannoel]

And also #17218

[kwannoel]

Opening a tracking issue for these improvements to explain.

[kwannoel]

Currently we support structured output, so the major work is complete. We can support graphviz as well, via the DOT format.

This can be done in the following way:

1. Use serde to convert the IR into petgraph::Graph. https://docs.rs/petgraph/latest/petgraph/. Just enable serde-1 feature flag.
2. From petgraph::Graph, this can be converted to Dot format: https://docs.rs/petgraph/latest/petgraph/dot/struct.Dot.html.

[lyang24]

Hi @kwannoel , I wound like to attempt on this issue - are we aiming to support logical plan and physical plan as dot format?

Use serde to convert the IR into petgraph::Graph. https://docs.rs/petgraph/latest/petgraph/. Just enable serde-1 feature flag.

looking at the code do we need to implement Deserialize for PrettySerde struct?

[kwannoel]

Hi @kwannoel , I wound like to attempt on this issue - are we aiming to support logical plan and physical plan as dot format?

Yes, via FORMAT DOT.

Use serde to convert the IR into petgraph::Graph. https://docs.rs/petgraph/latest/petgraph/. Just enable serde-1 feature flag.

looking at the code do we need to implement Deserialize for PrettySerde struct?

Yes, either implement Deserialize, or if you need more control over the way PrettySerde gets converted to petgraph::Graph, skip serde and manually convert it.

[lyang24]

send a draft - one more q which syntax is better explain (format graphviz) or explain (graphviz)?

[kwannoel]

send a draft - one more q which syntax is better explain (format graphviz) or explain (graphviz)?

Missed this, replied here: #19446 (comment). Thanks for your contribution!