diff options
Diffstat (limited to 'src/backend/optimizer/util/clauses.c')
| -rw-r--r-- | src/backend/optimizer/util/clauses.c | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index 97dacaaac19..19b5cf7b612 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -3447,12 +3447,15 @@ simplify_or_arguments(List *args, List *unprocessed_args; /* - * Since the parser considers OR to be a binary operator, long OR lists - * become deeply nested expressions. We must flatten these into long - * argument lists of a single OR operator. To avoid blowing out the stack - * with recursion of eval_const_expressions, we resort to some tenseness - * here: we keep a list of not-yet-processed inputs, and handle flattening - * of nested ORs by prepending to the to-do list instead of recursing. + * We want to ensure that any OR immediately beneath another OR gets + * flattened into a single OR-list, so as to simplify later reasoning. + * + * To avoid stack overflow from recursion of eval_const_expressions, we + * resort to some tenseness here: we keep a list of not-yet-processed + * inputs, and handle flattening of nested ORs by prepending to the to-do + * list instead of recursing. Now that the parser generates N-argument + * ORs from simple lists, this complexity is probably less necessary than + * it once was, but we might as well keep the logic. */ unprocessed_args = list_copy(args); while (unprocessed_args) |