Add documentation on EXPLAIN and EXPLAIN ANALYZE

[devanbenz]

Which issue does this PR close?

Closes #12088

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[devanbenz]

@alamb can overlaps happen in normal datafusion query plans? Or is this specific to InfluxDB? If possible could you point me in the direction of getting a parquet data-set with overlaps so I can run the EXPLAIN's locally?

[devanbenz]

Actually taking a look at the datafusion docs I'm not seeing DeduplicateExec in the public crate docs so I'm assuming this is not valid for core datafusion.
https://docs.rs/datafusion/latest/datafusion/physical_plan/union/struct.UnionExec.html?search=DeduplicateExec

[alamb]

This is awesome -- thank you @devanbenz

I took the liberty of pushing some commits to the branch that updated the first example and some wording -- let me know what you think. Maybe you could apply some of changes to the rest of the writeup too

I will try and find some more time later today or over the weekend to improve this documentation further with you.

[alamb]

I am going to try and document the analyze portion as well

[alamb]

@devanbenz -- this is so cool. Thank you for getting the ball rolling.

I wonder if you might be willing to try and take a shot at filling in this section for

SELECT "UserID", COUNT(*) FROM 'hits.parquet' GROUP BY "UserID" ORDER BY COUNT(*) DESC LIMIT 10;

?

The examples from our influx docs didn't translate very well to hits.parquet -- I apologize for not realizing that sooner

[devanbenz]

That sounds good to me! I'll have some time over the weekend to tackle it :)

[devanbenz]

@alamb Please let me know if theres anything else you would like for me to elaborate on within the aggregate plan. Taking a look at the original issue section I was seeing: #12088 (comment) which added some insight on exchange-based parallelism. Would you like for me to elaborate more on this?

[alamb]

@alamb Please let me know if theres anything else you would like for me to elaborate on within the aggregate plan. Taking a look at the original issue section I was seeing: #12088 (comment) which added some insight on exchange-based parallelism. Would you like for me to elaborate more on this?

Thank you @devanbenz -- this is great 🙏

I pushed some more clarifications but really a wonderful job explaining / linking.

[alamb]

Thank you @devanbenz -- this is really great.

I pushed another commit with some additional detail but this was a great job. Super helpful to get this going. Good teamwork! ✋

cc @NGA-TRAN @jstirnaman and @2010YOUY01

[alamb]

I think this is a great start and we can continue to iterate on the documentation as follow on PRs