On 15.01.2013 20:33, Robert Haas wrote:
> On Tue, Jan 15, 2013 at 1:10 PM, Heikki Linnakangas
>> Could we stash the counter e.g. in the root page of the index?
>
> That would require maintaining a counter per table rather than a
> single global counter, which would be bad because then we'd need to
> store one counter in shared memory for every table, rather than just
> one, period, which runs up against the fixed sizing of shared memory.
I was thinking of just adding a new field to the root page header, and
use that field as the counter. Something like:
XLogRecPtr
GetXLogRecPtrForTemp(void)
{ rootbuf = ReadBuffer(rel, GIST_ROOT_BLKNO); opaq = GistPageGetOpaque(BufferGetPage(rootbuf));
LockBuffer(rootbuf, GIST_EXCLUSIVE); nsn = opaq->counter++ UnlockReleaseBuffer(rootbuf) return nsn;
}
or perhaps we need to use locking mechanism for that, like just a new
global lwlock or spinlock, to avoid deadlocks if someone is just
splitting the root page. In any case, the fixed-sizedness of shared
memory isn't an issue here.
- Heikki