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
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