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.
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
