On Thu, Apr 11, 2019 at 6:06 AM Rafia Sabih <rafia.pghackers@gmail.com> wrote:
> Reading about it reminds me of this work -- TAG column storage(
http://www09.sigmod.org/sigmod/record/issues/0703/03.article-graefe.pdf).
> Isn't this storage system inspired from there, with TID as the TAG?
>
> It is not referenced here so made me wonder.
I don't think they're particularly similar, because that paper
describes an architecture based on using purely logical row
identifiers, which is not what a TID is. TID is a hybrid
physical/logical identifier, sometimes called a "physiological"
identifier, which will have significant overhead. Ashwin said that
ZedStore TIDs are logical identifiers, but I don't see how that's
compatible with a hybrid row/column design (unless you map heap TID to
logical row identifier using a separate B-Tree).
The big idea with Graefe's TAG design is that there is practically no
storage overhead for these logical identifiers, because each entry's
identifier is calculated by adding its slot number to the page's
tag/low key. The ZedStore design, in contrast, explicitly stores TID
for every entry. ZedStore seems more flexible for that reason, but at
the same time the per-datum overhead seems very high to me. Maybe
prefix compression could help here, which a low key and high key can
do rather well.
--
Peter Geoghegan