Write sql query detection for Postgres extremely slow

[urmomwx]

Steps to reproduce

Feed reasonably large SQL (in my case ~ 600 lines) file with multiple query statements to ActiveRecord::Base.connection.execute while using Postgresql as database adapter and wait for results. For a long time. It is working ok in Rails 6.0.4.8 but when migrating to rails 7.0.3 one of my tests hangs for more than 5 minutes.

To check it's the issue:

Fetched READ_QUERY from debugger just before the line that hangs:
https://github.com/rails/rails/blob/main/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb#L30

read_query_regex = /\A(?:[(\s]|(?m-ix:(?:--.*\n)|\/\*(?:[^*]|\*[^\/])*\*\/))*(?-mix:(?i-mx:close)|(?i-mx:declare)|(?i-mx:fetch)|(?i-mx:move)|(?i-mx:set)|(?i-mx:show)|(?i-mx:begin)|(?i-mx:commit)|(?i-mx:explain)|(?i-mx:release)|(?i-mx:rollback)|(?i-mx:savepoint)|(?i-mx:select)|(?i-mx:with))/
sql = STDIN.read
puts read_query_regex.match?(sql)

Expected behavior

It should perform the match in reasonable time, even in 1 second it would be fine

Actual behavior

It does not finish in at least 5 minutes keeping CPU at 100%.

System configuration

Rails version: 7.0.3

Ruby version: 3.1.2

[fatkodima]

I solved a similar problem for the query with comments - #45012. That was merged in 7.0.3, but seems like not solving you problem.
Can you paste your query? Or some other query that reproduces you problem?

[urmomwx]

Sure. Had to anonymize this old legacy script a bit. It still seems to be related to comments, for example removing first header comment makes it perform in low tens of milliseconds

0001_sample.sql.txt

[ghiculescu]

Could you see if removing the m helps for you? Ref #45011 (comment)