Add warning for poor compression ratio

[kpan2034]

Adds functionality to emit a warning to the user when the compression
ratio is "bad".

Currently, "bad" is defined to be when size after compression is higher
than after compression.

[kpan2034]

This change breaks roughly half our tests, since compressing chunks with only a few rows leads to a bad compression ratio. I considered adding this behind a GUC, which should probably be on by default, but except for testing I don't think there's ever a case where we want it to be OFF.

We can either:

• Add a GUC that enables this warning, and set it to OFF for all our tests.
• Update the affected tests with the warning that is emitted.

However, if we'd like to do more than just emit a warning in the future, then perhaps a GUC makes more sense, since that is something users might like to turn off. What are your thoughts on this @antekresic?

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.92%. Comparing base (59f50f2) to head (b8f1a65).
Report is 802 commits behind head on main.

Files with missing lines	Patch %	Lines
tsl/src/compression/api.c	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7756      +/-   ##
==========================================
+ Coverage   80.06%   81.92%   +1.85%     
==========================================
  Files         190      247      +57     
  Lines       37181    45390    +8209     
  Branches     9450    11343    +1893     
==========================================
+ Hits        29770    37187    +7417     
- Misses       2997     3733     +736     
- Partials     4414     4470      +56     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[antekresic]

This probably needs better wording, its too dry and doesn't even include name of the chunk.

[svenklemm]

agree with ante here that this needs a better error message
poor compression rate detected in chunk "xyz", the numbers could be moved into errdetail. Additionally you should probably use ereport here