Re: memory context for tuplesort return values

Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> Tom Lane wrote:
>> I've been modifying tuplesort.c to keep all the sort's local data in a
>> separate memory context, to simplify and speed up cleaning up the data
>> during tuplesort_end.

> Is it possible to make the TupleTableSlot not free the tuple
> automatically? AFAIR there is a parameter to the creation routine of a
> TupleTableSlot to make it so, but I don't know if it's possible to use
> in tuplesort.c's case at all.

The problem is that we specifically *want* the caller to free the tuple
when done with it. The API is essentially that tuplesort_gettuple is
passing ownership of the tuple over to the caller. Without this it
seems very hard to avoid an essentially useless palloc/pfree cycle
per tuple.

> Maybe it is possible to write some sort of magic number to the
> TupleTableSlot before it is destroyed, which could be checked if
> somebody tries to destroy it again, to warn them that the code should be
> changed to cope with the new order of things.

Oh, the coredump is reliable enough if you compiled with
MEMORY_CONTEXT_CHECKING ... we don't need any more frammishes there.

regards, tom lane