On Thu, Apr 21, 2016 at 1:39 PM Geoff Winkless <pgsqlad...@geoff.dj> wrote:
> On 21 April 2016 at 17:08, David G. Johnston <david.g.johns...@gmail.com> > wrote: > > I have little experience (and nothing practical) with columnar store but > at > > a high level I don't see the point. I would hope that anyone interested > in > > working on a columnar store database would pick an existing one to > improve > > rather than converting a very successful row store database into one. > And I > > don't immediately understand how a dual setup would even be viable - it > > seems like you'd have to re-write so much > > of the code the only thing left would be the SQL parser. > > To be fair, I'd say that this "only thing" would be pretty huge. The > cost of changing databases is often prohibitive (or nearly so) because > the parser isn't _quite_ the same, and if the sort of gains that are > bandied about could really be achieved just by choosing columnar > storage for certain tables without having to rewrite large chunks of > code that would be a very big win. > > I certainly agree that changing the store to columnar-only makes > little sense though, because it would alienate a lot (I would suggest > the majority) of users whose data fits far better into a row model. > > FWIW, looking at the cstore_fdw extension did get me quite excited > (because I have an inkling that quite a lot of our queries might > benefit from such a feature) until I saw that DELETEs aren't possible, > which would invalidate most of the wins for us because of the > subsequent massive cost of modifying data. > > There's also an interesting document from the monet_db guys about how > the wins to be gained just by using cstore_fdw (rather than moving to > a native column-store) aren't as high as you would hope. I have a > feeling that would remain the case even if the store were integrated. > > > https://www.monetdb.org/content/citusdb-postgresql-column-store-vs-monetdb-tpc-h-shootout > " the margin by which MonetDB outperforms cstore_ftw shows that only > switching storage models alone is probably not enough" > I think the gains are really high as with big data caching is usually not really possible. But of course cstore_fdw should perform better when caching is feasible. > > Geoff > (Disclaimer: I've no connection to MonetDB in any way) >
