Hi, On 2019-05-15 15:07:13 -0400, Alvaro Herrera wrote: > On 2019-May-15, Andres Freund wrote: > > > - blk = ItemPointerGetBlockNumber(tid); > > - if (blk >= RelationGetNumberOfBlocks(relation)) > > - elog(ERROR, "block number %u is out of range for relation > > \"%s\"", > > - blk, RelationGetRelationName(relation)); > > > > Which I dutifully rewrote. But I'm actually not sure it's safe at all > > for heap to rely on t_ctid links to be valid. What prevents a ctid link > > to point to a page that's since been truncated away? > > Umm .. IIUC all index entries for truncated pages should have been > removed prior to the truncation. Otherwise, how would those index > entries not become immediately data corruption the instant the heap is > re-grown to cover those truncated pages? So I think if the TID comes > directly from user then this is a check worth doing, but if the TID > comes from an index, then it isn't.
I'm not sure how indexes come into play here? For one, I don't think heap_get_latest_tid() is called straight on a tuple returned from an index scan. But also, I don't think that'd change much - it's not the tid that's passed to heap_get_latest_tid() that's the problem, it's the tuples it chains to via t_ctid. Greetings, Andres Freund
