Alvaro Herrera <[email protected]> wrote: > - 0008 to 0010 are as posted by Antonin; they are unchanged, except for > fixes for the problems pointed out by Mihail. Antonin, I would > appreciate it if you want to change the "reform" bit in 0007 as > discussed.
I've taken a look, but not sure if the tuple slots help here. In heapam_relation_copy_for_cluster(), both table_scan_getnextslot() and index_getnext_slot() call ExecStoreBufferHeapTuple() -> tts_buffer_heap_store_tuple(), which AFAICS do not deform the tuple. Then ExecFetchSlotHeapTuple() is used to retrieve the tuple, but again, the underlying slot (TTSOpsBufferHeapTuple) handles it by copying rather than deforming / forming. Thus I think the explicit "reforming" currently does not add any performance overhead. Of course, we can still use the slots, and do the following: 1) enforce tuple deforming (by calling slot_getallattrs()), 2) set the dropped attributes to NULL, 3) use ExecStoreVirtualTuple() to store the tuple into another slot and 4) get the heap tuple from the other slot. Should I do that? I'm asking because I wasn't sure if you're concerned about performance or coding (or both). Whatever approach we take, I see two more opportunities for better performance: 1. Do the "reforming" only if there are some dropped columns. (AFAICS even the old CLUSTER / VACUUM FULL did not check this.) 2. Get rid of the values of dropped columns earlier, so that the dropped values are not put into the tuplestore (likewise, I think that CLUSTER / VACUUM FULL did not care.) Besides that, I think that heap_form_tuple() should set the values of dropped columns to NULL by default, or do I miss something? Anyway, this should be addressed by a separate patch. -- Antonin Houska Web: https://www.cybertec-postgresql.com
