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Cluster Features and Commit order of transactions

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: pgsql-cluster-hackers(at)postgresql(dot)org
Subject: Cluster Features and Commit order of transactions
Date: 2010-04-11 08:36:22
Message-ID: 4BC18A06.7000603@2ndquadrant.com (view raw or flat)
Thread:
Lists: pgsql-cluster-hackers
I just applied many updates to the 
http://wiki.postgresql.org/wiki/ClusterFeatures page:

-The description of "Function scan push-down" and "Modification trigger 
into core" now reflect discussion here on the list last month
-Wrote initial descriptions based on my own understanding of the issues 
for "DDL Triggers", "Dynamic shared memory allocation", "XID feed", and 
"Creation of primary keys online"

Please directly correct those or let me know if there's anything I did 
that that doesn't look right.  We're almost done with getting this 
document readable now.

The main still confusing entry there is "Commit order of transactions".  
I can't really make out what the point of that is supposed to be.  How 
is it that these "commit in reverse order" situations pop up?  I think 
this one may have prematurely wandered too far into implementation 
details too.  The idea of having a lookup table to associate xid and 
timestamp would be helpful in a number of cases (that has popped up as 
useful for Hot Standby too).  But I have my doubts about whether 
scraping backwards in the WAL to get that data is ever going to be an 
acceptable way to handle that.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com   www.2ndQuadrant.us


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