Re: 7.4 - FK constraint performance

ow <oneway_111@yahoo.com> writes:
> schemaname    tablename    attname    null_frac    avg_width    n_distinct    most_common_vals
> most_common_freqs    histogram_bounds    correlation
> my    large    small_id    0    4    10    {7,3,5,1,4,2,8,10,6,9}
> {0.108667,0.105,0.104333,0.101333,0.100667,0.0983333,0.0983333,0.0983333,0.094,0.091}
>     0.0597573

According to this entry, your small_id column only contains the ten
values 1..10, roughly evenly distributed.  So why are you probing for
239??

The planner is certainly going to estimate a probe for an unspecified
value as retrieving 10% of the table, and under that assumption it's
quite right to use a seqscan.

If this estimate is not right, perhaps you could give us a more accurate
view of the column statistics?
        regards, tom lane