The following review has been posted through the commitfest application:
make installcheck-world: not tested
Implements feature: not tested
Spec compliant: not tested
Documentation: not tested
I have a very serious concern about the current patch set. as someone who has faced transaction id wraparound in the
past.
I can start by saying I think it would be helpful (if the other issues are approached reasonably) to have 64-bit xids,
butthere is an important piece of context in reventing xid wraparounds that seems missing from this patch unless I
missedsomething.
XID wraparound is a symptom, not an underlying problem. It usually occurs when autovacuum or other vacuum strategies
haveunexpected stalls and therefore fail to work as expected. Shifting to 64-bit XIDs dramatically changes the sorts
ofproblems that these stalls are likely to pose to operational teams. -- you can find you are running out of storage
ratherthan facing an imminent database shutdown. Worse, this patch delays the problem until some (possibly far later!)
time,when vacuum will take far longer to finish, and options for resolving the problem are diminished. As a result I
amconcerned that merely changing xids from 32-bit to 64-bit will lead to a smaller number of far more serious outages.
What would make a big difference from my perspective would be to combine this with an inverse system for warning that
thereis a problem, allowing the administrator to throw warnings about xids since last vacuum, with a configurable
threshold. We could have this at two billion by default as that would pose operational warnings not much later than we
havenow.
Otherwise I can imagine cases where instead of 30 hours to vacuum a table, it takes 300 hours on a database that is
shorton space. And I would not want to be facing such a situation.
The new status of this patch is: Waiting on Author