Re: pgstattuple locking fix

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp> writes:
> > Here is a trivial fix of locking issue in pgstattuple().
>
> Hmm, is this really a bug, and if so how far back does it go?
> I'm thinking that having a pin on the buffer should be enough to
> call PageGetHeapFreeSpace.

Hmm... we might use pd_upper and pd_lower at different times,
but the error is ok for pgstattuple purpose.
(It might be dangerous for tuple insertion, though.)
Inconsistent usage of locks is confusable -- remove them, please.

Index: contrib/pgstattuple/pgstattuple.c
===================================================================
--- contrib/pgstattuple/pgstattuple.c (HEAD)
+++ contrib/pgstattuple/pgstattuple.c (working copy)
@@ -289,9 +289,7 @@
while (block <= tupblock)
{
buffer = ReadBuffer(rel, block);
- LockBuffer(buffer, BUFFER_LOCK_SHARE);
stat.free_space += PageGetHeapFreeSpace((Page) BufferGetPage(buffer));
- LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buffer);
block++;
}

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center