Fix set explain regex

[jasonmp85]

What does this PR do?

Reapplies the feature added in #20106, addressing the exponential runtime that certain SQL payloads could cause in the original implementation.

Notably, it removes repetition operators from inner groups in the regex and refactors it so such repetition appears in the outer groupings of inner alternations.

Testing

To test this, I wired up sqlsmith to a Python script which could generate the whole SET syntax. Between zero and ten SET statements were prepended to every sqlsmith-produced statement, as well as inline comments, at random. Over 100,000 statements were processed in this manner, and across many such runs, no exponential behavior was observed with the new regex (the old regex hung regularly, and quickly).

Performance

One such run of over 200,000 statements is illustrated with the below histogram. The buckets are runtime, in nanoseconds.

                      ┌                                        ┐ 
   [    0.0,  5000.0) ┤▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 173761   
   [ 5000.0, 10000.0) ┤▇▇▇▇▇▇▇▇ 42857                            
   [10000.0, 15000.0) ┤▇ 6345                                    
   [15000.0, 20000.0) ┤ 1244                                     
   [20000.0, 25000.0) ┤ 341                                      
   [25000.0, 30000.0) ┤ 162                                      
   [30000.0, 35000.0) ┤ 52                                       
   [35000.0, 40000.0) ┤ 22                                       
   [40000.0, 45000.0) ┤ 12                                       
   [45000.0, 50000.0) ┤ 4                                        
   [50000.0, 55000.0) ┤ 4                                        
   [55000.0, 60000.0) ┤ 3                                        
   [60000.0, 65000.0) ┤ 2                                        
   [65000.0, 70000.0) ┤ 0                                        
   [70000.0, 75000.0) ┤ 0                                        
   [75000.0, 80000.0) ┤ 0                                        
   [80000.0, 85000.0) ┤ 0                                        
   [85000.0, 90000.0) ┤ 1                                        
                      └                                        ┘ 
                                      Frequency

Motivation

I'd like to ship this feature and had to pull it before because of it pegging the CPU to 100%.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[jasonmp85]

The performance benchmark was around the call to trim the SET statements from the SQL using the new regex. The vast majority of calls run in 5–10 microseconds on my laptop.

Additionally, after determining a snippet of affected SQL using the fuzzer, I added it to our unit tests. Without the fix, it hangs indefinitely. With the fix the whole suite runs imperceptibly fast.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.33%. Comparing base (0245920) to head (43636d8).
Report is 1 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
confluent_platform	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
postgres	93.22% <100.00%> (+3.62%)	⬆️
presto	?
solr	?
tomcat	?
weblogic	?

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Review from nenadnoveljic is dismissed. Related teams and files:

• database-monitoring-agent
  • postgres/changelog.d/20319.fixed
  • postgres/datadog_checks/postgres/explain_parameterized_queries.py
  • postgres/datadog_checks/postgres/statement_samples.py
  • postgres/datadog_checks/postgres/util.py
  • postgres/tests/test_statements.py
  • postgres/tests/test_unit.py

[jasonmp85]

@nenadnoveljic I thought this auto-merged but something happened with a test. Between being sick and the US holiday, your review became stale… can you re-post approval when you have the chance?