Re: INSERT...ON DUPLICATE KEY LOCK FOR UPDATE

On Sat, Sep 21, 2013 at 05:07:11PM -0700, Peter Geoghegan wrote:
> In the average/uncontended case, the subxact example bloats less than
> all alternatives to my design proposed to date (including the "unborn
> heap tuple" idea Robert mentioned in passing to me in person the other
> day, which I think is somewhat similar to a suggestion of Heikki's
> [1]). The average case is very important, because in general
> contention usually doesn't happen.

This thread had a lot of discussion about bloating.  I wonder, does the
code check to see if there is a matching row _before_ adding any data? 
Our test-and-set code first checks to see if the lock is free, then if
it it is, it locks the bus and does a test-and-set.   Couldn't we easily
check the indexes for matches before doing any locking?  It seems that
would avoid bloat in most cases, and allow for a simpler implementation.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + It's impossible for everything to be true. +