Re: Read Uncommitted

On Wed, Dec 18, 2019 at 10:18 AM Simon Riggs <simon@2ndquadrant.com> wrote:
> This was my first concern when I thought about it, but I realised that by taking a snapshot and then calculating xmin
normally,this problem would go away.
 

Why? As soon as a transaction aborts, the TOAST rows can be vacuumed
away, but the READ UNCOMMITTED transaction might've already seen the
main tuple. This is not even a particularly tight race, necessarily,
since for example the table might be scanned, feeding tuples into a
tuplesort, and then the detoating might happen further up in the query
tree after the sort has completed.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company