Re: Parameterized paths vs index clauses extracted from OR clauses

On Thu, Feb 28, 2013 at 3:03 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

Whichever way we go, the resulting patch is likely to be too large and
invasive for me to feel terribly comfortable about back-patching it into
9.2.  AFAICT this issue only arises for indexquals extracted out of
larger OR conditions, so maybe it's not worth taking such a risk for.

EnterpriseDB has received a number of complaints from our customers
resulting from planner behavior changes which were back-patched; so I
am not sanguine about back-patching unless the situation is pretty
darn dire and the fix is pretty darn near certain to be an improvement
in every case.  As we have discussed many times here and on
pgsql-performance, DBAs seem to prefer a query plan that's the same
every time, even if it's bad.  Updating to get a security fix and
having plans change under you proves to be an unpleasant surprise.

It also weakens our argument (per versioning policy) that patch releases are *totally safe* and are something you can apply without extensive testing and QA per http://www.postgresql.org/support/versioning/ .

I have enough trouble getting people to update as it is.

I'd be interested in being able to turn on fixes/enhancements, but having behaviour changes that aren't clear wins in all cases turned on by default seems likely to weaken trust from users who're already way too leery of updating.

-- Craig Ringer                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services