On Mon, Jun 10, 2019 at 12:15 PM Alex <zhihui.fan1...@gmail.com> wrote:
> HEAPTUPLE_RECENTLY_DEAD, /* tuple is dead, but not deletable yet */ > > It is a tuple which has been deleted AND committed but before the delete > there is a transaction started but not committed. Let call this transaction > as Transaction A. > > if we create index on this time, Let's call this index as Index A， it > still index this record. my question is why need this. > > In this case, the changes of the tuple is not visible yet. Now suppose, your transaction A is serializable and you've another serializable transaction B which can see the index A. It generates a plan that requires to fetch the deleted tuple through an index scan. If the tuple is not present in the index, how are you going to create a conflict edge between transaction A and transaction B? Basically, you need to identify the following clause to detect serializable conflicts: Transaction A precedes transaction B. (Because, transaction A has deleted a tuple and it's not visible to transaction B) -- Thanks & Regards, Kuntal Ghosh EnterpriseDB: http://www.enterprisedb.com
