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Re: [HACKERS] EXPLAIN doesn't explain operations on inheritance trees

From: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
To: tgl(at)sss(dot)pgh(dot)pa(dot)us (Tom Lane)
Cc: pgsql-hackers(at)hub(dot)org
Subject: Re: [HACKERS] EXPLAIN doesn't explain operations on inheritance trees
Date: 1998-07-15 15:10:29
Message-ID: 199807151510.LAA04863@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
> If I create a class A and make subclasses A1 and A2, then
> I get useful explanations when I say "EXPLAIN SELECT * FROM A1 ..."
> but not if I ask about a query on the inheritance tree A*.
> 
> tgl=> EXPLAIN SELECT * FROM A* WHERE accountid = 3;
> NOTICE:  QUERY PLAN:
> 
> Append  (cost=0.00 size=0 width=0)
> 
> EXPLAIN
> 
> With "explain verbose" it is possible to see that the APPEND plan
> has substructure, but it's hard to see what's going on in that format.
> How come plain "explain" doesn't show the subnodes of an APPEND plan?

I have just applied a patch to fix this.  Append is an unusual node,
because instead of checking left/right plans, you have to loop through a
list of plans.  EXPLAIN did not do this, nor did cost computations and
pprint().

Should be better now.  

I renamed all the Append structure names because they were very
confusing to me.  I had created some of them for UNION, but named the
badly.

-- 
Bruce Momjian                          |  830 Blythe Avenue
maillist(at)candle(dot)pha(dot)pa(dot)us              |  Drexel Hill, Pennsylvania 19026
  +  If your life is a hard drive,     |  (610) 353-9879(w)
  +  Christ can be your backup.        |  (610) 853-3000(h)

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