On Thu, Jul 24, 2014 at 3:42 PM, Rohit Goyal <rhtgyl...@gmail.com> wrote: > This was really -2 helpful.
I'm not sure what it means to be -2 helpful. Hopefully it's a good thing. > 1. Can I use this xmin variable directly anytime anywhere in my code as it > is a global variable. I don't really know what you're asking. If you want a tutorial on how global variables work in C, this is the wrong mailing list to ask about that. > 2. What is the difference b/w recentXmin and RecentGlobalXmin. I read the > description but any small detail can clear my mind. :) RecentXmin is the oldest transaction ID that was still running as of the last time it was updated. RecentGlobalXmin is the oldest transaction ID that was part of somebody's snapshot as of the last time it was updated. Transaction IDs older than RecentXmin can be assumed not to be running, but there could be still-running transactions that can't see the effected of some committed transaction whose ID precedes RecentXmin. Transaction IDs older than RecentGlobalXmin are no longer running, and furthermore any the effects of any such transactions which went on to commit are guaranteed to be visible to the snapshots of all currently-running transactions, and all future transactions. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
