Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer

> Bruce Momjian wrote:
> > 
> > Let me tell you why I don't think this is a bug.  The optimizer will
> > choose ordered results over unordered results if the costs are the same.
> > In this case, the cost of the query is zero, so it chose to use the
> > index because the index produces an ordered result.
> > 
> > This works well for un-vacuumed tables, because it thinks everything is
> > zero cost, and chooses the index.
> 
> Agreed, this is ok as long as
> 
> vac=> create table table1 (field1 int);
> CREATE
> vac=> insert into table1 values (1);
> INSERT 1583349 1
> vac=> create index i_table1__field1 on table1 (field1);
> CREATE
> vac=> explain select * from table1 where field1 = 1;
> NOTICE:  QUERY PLAN:
> 
> Seq Scan on table1  (cost=1.03 size=1 width=4)
> 
> - SeqScan is used for small tables.
> 
> So, only bug reported is left.
> 
> Vadim
> 

Fixed:test=> explain select * from table1 where field1 = 1;NOTICE:  QUERY PLAN:Index Scan using i_table1__field1 on
table1 (cost=0.00 size=0 width=4)EXPLAINtest=> explain select * from table1 where field1 = -1;NOTICE:  QUERY PLAN:Index
Scanusing i_table1__field1 on table1  (cost=0.00 size=0 width=4)
 

The function fixing it is in gram.y:static Node *doNegate(Node *n){    if (IsA(n, A_Const))    {        A_Const *con =
(A_Const*)n;        if (con->val.type == T_Integer)        {            con->val.val.ival = -con->val.val.ival;
  return n;        }        if (con->val.type == T_Float)        {            con->val.val.dval = -con->val.val.dval;
        return n;        }    }    return makeA_Expr(OP, "-", NULL, n);}
 


It tries to merge the negative into the constant.  We already had
special '-' handling in the grammer, so I just call this function,
rather than doing makeA_Expr in all cases.

Committed.

--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
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