Parser: fix exponential parse time on table-factor paren chains#2372
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`parse_table_factor` speculatively parses `(...)` as a derived table; on failure it rewinds and falls through to `parse_table_and_joins`, which recurses back into `parse_table_factor` and re-attempts the same speculative parse at every deeper paren. Both arms walk the remaining chain, so on inputs like `SELECT 1 FROM ((((...` work doubles per level. Caching the position at which the speculative arm failed short-circuits the second descent. Measured on `GenericDialect` with `with_recursion_limit(256)`, release build: | N | Before | After | |----|---------|--------| | 10 | 20 ms | 57 us | | 20 | 820 ms | 119 us | | 25 | 2.8 s | 281 us | | 30 | 7.9 s | 345 us |
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parse_table_factorspeculatively parses(...)as a derived table; onfailure it rewinds and falls through to
parse_table_and_joins, whichrecurses back into
parse_table_factorand re-attempts the samespeculative parse at every deeper paren. Both arms walk the remaining
chain, so on inputs like
SELECT 1 FROM ((((...work doubles per level.Caching the position at which the speculative arm failed short-circuits
the second descent.
Measured on
GenericDialectwithwith_recursion_limit(256), releasebuild: