fix(storage): iter metrics should include init duration

[skyzh]

Signed-off-by: Alex Chi iskyzh@gmail.com

I hereby agree to the terms of the Singularity Data, Inc. Contributor License Agreement.

What's changed and what's your intention?

Previously we only take scan duration into account, which is not accurate enough to reflect the real time taken by each iterator.

Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in ./risedev check (or alias, ./risedev c)

Refer to a related PR or issue link (optional)

[skyzh]

Also we're using mininstant (thanks to @breezewish for recommendation!) for Instant, which should reduce overhead of collecting time metrics.

[codecov]

Codecov Report

Merging #3462 (e1d9086) into main (6596612) will decrease coverage by 0.00%.
The diff coverage is 56.25%.

@@            Coverage Diff             @@
##             main    #3462      +/-   ##
==========================================
- Coverage   74.48%   74.48%   -0.01%     
==========================================
  Files         770      770              
  Lines      108126   108140      +14     
==========================================
+ Hits        80542    80546       +4     
- Misses      27584    27594      +10     

Flag	Coverage Δ
rust	74.48% <56.25%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/storage/src/monitor/monitored_store.rs	1.88% <0.00%> (-0.06%)	⬇️
src/storage/src/monitor/state_store_metrics.rs	86.38% <100.00%> (+0.30%)	⬆️
src/frontend/src/expr/utils.rs	98.74% <0.00%> (-0.51%)	⬇️
src/connector/src/filesystem/file_common.rs	80.35% <0.00%> (-0.45%)	⬇️
src/meta/src/rpc/server.rs	79.95% <0.00%> (-0.24%)	⬇️
src/meta/src/manager/id.rs	94.94% <0.00%> (ø)

📣 Codecov can now indicate which changes are the most critical in Pull Requests. Learn more

[skyzh]

One interesting finding is that iterator creation + fetching first block is taking much more time than actual scanning, which indicates some issues. maybe related to #3459