psql :optimized_sql strategy now updates a single row #177
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The planner may choose to generate a plan that executes a nested loop over the LIMITing subquery, causing more UPDATEs than LIMIT
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This prevents a -single- worker from taking all jobs.
The subquery should return a row using
LIMIT 1. But, it sometimes return multiple rows. Why?Because the planner may choose to generate a plan that executes a nested loop over the LIMITing subquery, causing more UPDATEs than LIMIT.
The solution is to materialize the selection into a CTE.
fixes collectiveidea/delayed_job#915
fixes #143
see detailed explanation
credits to @koshigoe and @fsateler.