Re: 10x rowcount mis-estimation favouring merge over nestloop

[Abhijit Menon-Sen <ams(at)oryx(dot)com>]

At 2006-11-10 01:15:24 -0500, tgl(at)sss(dot)pgh(dot)pa(dot)us wrote:
>
> it seems that "field<=12" is true for a much smaller fraction of the
> rows satisfying (part!='' or value ilike '%,%') than for the general
> population of rows in the header_fields table.

Indeed. One-sixth of the rows in the entire table match field<=12, but
only one-fifteenth of the rows matching the part/value condition also
match field<=12.

> There's been some speculation about obtaining stats on partial indexes
> as a substitute for solving the general problem of correlation stats,

Oh. So my partial index's rowcount isn't being considered at all? That
explains a lot. Ok, I'll just run the query with mergejoin and seqscan
disabled. (I can't think of much else to do to speed it up, anyway.)

Thanks.

-- ams