Re: GiST VACUUM

On Fri, Jul 13, 2018 at 10:10 AM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> I'm still a bit scared about using pd_prune_xid to store the XID that
> prevents recycling the page too early. Can we use some field in
> GISTPageOpaqueData for that, similar to how the B-tree stores it in
> BTPageOpaqueData?

What's your reason for being scared? It seems to me that the
alternatives being proposed (altering the size of the special space,
or sometimes repurposing a field for some other purpose) have their
own associated scariness.

If I had my druthers, I'd nuke pd_prune_xid from orbit -- it's a piece
of seemingly heap-specific data that is kept in the generic page
header rather than in the heap's special space. Other AMs like btree
or zheap may have different needs; one size does not fit all. That
said, since getting rid of pd_prune_xid seems impractical, maybe it
makes more sense to reuse it than to insist on leaving it idle and
consuming space elsewhere in the page.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company