ReadRecentBuffer() doesn't work for local buffers, i.e. for temp tables.
The bug is pretty clear if you look at the code:
if (BufferIsLocal(recent_buffer))
{
- bufHdr = GetBufferDescriptor(-recent_buffer - 1);
+ bufHdr = GetLocalBufferDescriptor(-recent_buffer - 1);
The code after that looks suspicious, too. It increases the usage count
even if the buffer was already pinned. That's different from what it
does for a shared buffer, and different from LocalBufferAlloc(). That's
pretty harmless, just causes the usage count to be bumped more
frequently, but I don't think it was intentional. The ordering of
bumping the usage count, the local ref count, and registration in the
resource owner are different too. As far as I can see, that makes no
difference, but I think we should keep this code as close as possible to
similar code used elsewhere, unless there's a particular reason to differ.
I propose the attached to fix those things.
I tested this by adding this little snippet to a random place where we
have just read a page with ReadBuffer:
diff --git a/src/backend/access/heap/heapam.c
b/src/backend/access/heap/heapam.c
index aab8d6fa4e5..c4abdbc96dd 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -403,6 +403,14 @@ heapgetpage(TableScanDesc sscan, BlockNumber page)
RBM_NORMAL, scan->rs_strategy);
scan->rs_cblock = page;
+ {
+ bool still_ok;
+
+ still_ok =
ReadRecentBuffer(scan->rs_base.rs_rd->rd_locator, MAIN_FORKNUM, page,
scan->rs_cbuf);
+ Assert(still_ok);
+ ReleaseBuffer(scan->rs_cbuf);
+ }
+
if (!(scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE))
return;
Without the fix, the assertion is fails quickly on "make check".
- Heikki
