Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer - Mailing list pgsql-hackers

From Bruce Momjian
Subject Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer
Date
Msg-id 199903181856.NAA05806@candle.pha.pa.us
Whole thread Raw
In response to Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer  (Vadim Mikheev <vadim@krs.ru>)
List pgsql-hackers
> 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.

My guess is that the creation of the index updates the table size
statistics.

However, when I see zero size, I don't know if it is accurate, or if
someone has added rows since the last vacuum/index creation, so I think
it is correct to use an index on a zero-length table if it is
appropriate.  If the size is 1, I will assume that number is accurate,
and do a sequential scan.

Does that make sense?


--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026
 


pgsql-hackers by date:

Previous
From: Bruce Momjian
Date:
Subject: Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer
Next
From: Vadim Mikheev
Date:
Subject: Re: [HACKERS] Re: [BUGS] General Bug Report: Bug in optimizer