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b99551832e
Putting a reference to an expanded-format value into a Const node would be a bad idea for a couple of reasons. It'd be possible for the supposedly immutable Const to change value, if something modified the referenced variable ... in fact, if the Const's reference were R/W, any function that has the Const as argument might itself change it at runtime. Also, because datumIsEqual() is pretty simplistic, the Const might fail to compare equal to other Consts that it should compare equal to, notably including copies of itself. This could lead to unexpected planner behavior, such as "could not find pathkey item to sort" errors or inferior plans. I have not been able to find any way to get an expanded value into a Const within the existing core code; but Paul Ramsey was able to trigger the problem by writing a datatype input function that returns an expanded value. The best fix seems to be to establish a rule that varlena values being placed into Const nodes should be passed through pg_detoast_datum(). That will do nothing (and cost little) in normal cases, but it will flatten expanded values and thereby avoid the above problems. Also, it will convert short-header or compressed values into canonical format, which will avoid possible unexpected lack-of-equality issues for those cases too. And it provides a last-ditch defense against putting a toasted value into a Const, which we already knew was dangerous, cf commit |
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| .. | ||
| bitmapset.h | ||
| execnodes.h | ||
| lockoptions.h | ||
| makefuncs.h | ||
| memnodes.h | ||
| nodeFuncs.h | ||
| nodes.h | ||
| params.h | ||
| parsenodes.h | ||
| pg_list.h | ||
| plannodes.h | ||
| primnodes.h | ||
| print.h | ||
| readfuncs.h | ||
| relation.h | ||
| replnodes.h | ||
| tidbitmap.h | ||
| value.h | ||