On Wed, Oct 12, 2011 at 12:35 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Hm. I had been supposing that lossless compress functions would just be > no-ops. If that's not necessarily the case then we might need something > different from the opclass's decompress function to get back the > original data. However, that doesn't really solve the problem I'm > concerned about, because the existence and use of such a function would > be entirely internal to GiST. There still needs to be a way for the > planner to know which opclasses support data retrieval. And I do *not* > want to see us hard-wire "the presence of opclass function 8 means a > GiST opclass can return data" into the planner. > > Maybe, instead of a simple constant amcanreturn column, we need an AM > API function that says whether the index can return data. > I like idea of such AM API function. Since single multicolumn index can use multiple opclasses, AM API function should also say *what* data index can return.
------ With best regards, Alexander Korotkov.
