On 14 December 2015 at 15:27, Chapman Flack <c...@anastigmatix.net> wrote:
> On 12/14/15 01:50, Craig Ringer wrote: > > > pg_upgrade means you can't just redefine the current toast bits so the > > compressed bit means "data is compressed, check first byte of varlena > data > > for algorithm" because existing data won't have that, the first byte will > > be the start of the compressed data stream. > > Is there any small sequence of initial bytes you wouldn't ever see in PGLZ > output? Either something invalid, or something obviously nonoptimal > like run(n,'A')||run(n,'A') where PGLZ would have just output run(2n,'A')? > > I don't think we need to worry, since doing it per-column makes this issue go away. Per-Datum compression would make it easier to switch methods (requiring no table rewrite) at the cost of more storage for each varlena, which probably isn't worth it anyway. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
