Re: Hot Standby query cancellation and Streaming Replication integration

Greg Smith wrote:
> You can think of the idea of passing an xmin back from the standby as 
> being like an auto-tuning vacuum_defer_cleanup_age. It's 0 when no 
> standby queries are running, but grows in size to match longer ones. And 
> you don't have to have to know anything to set it correctly; just toggle 
> on the proposed "feedback xid from the standby" feature and you're safe.

Yes, there is no question there is value in passing the xid back to the
master.  My point is that it is like your blog entry:
http://blog.2ndquadrant.com/en/2010/02/tradeoffs-in-hot-standby-deplo.html

you can't have all the options:
1.  agressive vacuum on master2.  fast recovery of slave3.  no query cancel on slave

Again, pick two.  Passing the xid back to the master gives you #2 and
#3, and that might be good for some people, but not others.  Do we have
any idea which options most administrators would want?  If we get xid
passback to the master, do we keep the other configuration options?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
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