On 21 December 2015 at 02:14, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote:
> Jim Nasby wrote: > > On 11/23/15 5:06 PM, Peter Geoghegan wrote: > > >I realize that the second scan performed by lazy_vacuum_heap() only > > >visits those pages known to contain dead tuples. However, the > > >experience of seeing problems with the random sampling of ANALYZE > > >makes me think that that might not be very helpful. There is no good > > >reason to think that there won't be a uniform distribution of dead > > >tuples across the heap, and so only visiting pages known to contain > > >dead tuples might be surprisingly little help even when there are > > >relatively few VACUUM-able tuples in the table. > > > > Even worse is if you can't fit all the dead TIDs in memory and have to do > > multiple passes for no reason... > > Since BRIN indexes cannot be primary keys nor unique keys, it's hard to > be convinced that the use case of a table with only BRIN indexes is > terribly interesting. > Given BRIN's characteristics, such a table design is compelling when the table is very large, yet possible only for certain use cases. -- Simon Riggs http://www.2ndQuadrant.com/ <http://www.2ndquadrant.com/> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
