Re: Stuck using Sequential Scan

On Tue, 2004-09-07 at 22:32, Jeremy M. Guthrie wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> I have a problem where I have the table format listed below.  I have the
> primary key tsyslog_id and the index built against it.  However, when I
> select a unique row, it will only ever do a seq scan even after I turn off
> all other types except indexscan.  I understand you cannot fully turn off seq
> scan.
...
> I cannot run vacuum more than once a day because of its heavy IO penalty.  I
> run analyze once an hour.  However, if I run analyze then explain, I see no
> difference in the planners decisions.  What am I missing?
>
>
> TSyslog=# \d syslog_tarchive;
>                                         Table "public.syslog_tarchive"
>    Column   |          Type          |
> Modifiers
> - ------------+------------------------+-------------------------------------------------------------------------
>  tsyslog_id | bigint                 | not null default
...
>
> TSyslog=# explain select * from tsyslog where tsyslog_id=431650835;

That constant is INTEGER, whereas the column is BIGINT; there is no
automatic conversion in this case, so the planner does not realise the
index is usable for this query (I think 8.0 solves this).

Try: select * from tsyslog where tsyslog_id=431650835::BIGINT;

--
Oliver Elphick                                          olly@lfix.co.uk
Isle of Wight                              http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA  92C8 39E7 280E 3631 3F0E  1EC0 5664 7A2F A543 10EA
                 ========================================
     "I am crucified with Christ; nevertheless I live; yet
      not I, but Christ liveth in me; and the life which I
      now live in the flesh I live by the faith of the Son
      of God, who loved me, and gave himself for me."
                                         Galatians 2:20