SPI_keepplan with configurable memory context

[yrashk]

Does anybody know a rationale (if any) for not having a version of SPI_keepplan that would allow saving the plan in a specified memory context rather than CacheMemoryContext?

[yrashk]

@robertmhaas provided a great answer on Discord:

When you call SPI_keepplan(), it calls SavedCachePlan() on each CachedPlanSource, which adds it to a global linked list called saved_plan_list. So if a saved plan where destroyed by deleting the memory context that contains it, then saved_plan_list would end up with garbage pointers in it, and the next access to that list would probably seg fault. So the purpose of putting the plan under CachedMemoryContext is to make sure that you always get rid of the plan using SPI_freeplan rather than any other tricky method. In theory, if you put it in some other memory context but still always explicitly used SPI_freeplan, everything would be fine. But if that other memory context were ever deleted, you'd have a disaster. So we use CacheMemoryContext, which is never deleted.

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Thanks!