Fix #395 - LIMIT Pushdown -> force single task execution #396
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LIMIT is now always pushed down to Postgres with single-task execution enforced, so the EXPLAIN test should expect no LIMIT in the DuckDB plan
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To fix
LIMITreturning more than the expected rows, this PR guarantees single-task/thread execution when LIMIT Pushdown occurs.Relevant issues: #380 #395
BACKGROUND:
LIMIT Pushdown introduced big optimization but also an issue where
LIMIT Nwould return more thanNresults, due to some thread and tasking.Initially fixed in #330 , where we only apply LIMIT Pushdown, if
max_threads == 1. This did not cover all cases.As suggested by @Mytherin already on the PR above, it may be better to set threads and tasks to 1, when LIMIT optimization can be applied. This PR does that.
Before fixes applied,
Test 4insidetest/sql/storage/limit_parallel_bug.testwas failing by returning more than 1 row. To recreate #395This PR removes the check made in #330 in favor of setting the amount of threads and tasks.