On Wed, Oct 17, 2012 at 6:14 AM, Pedro Jiménez Pérez
<p.jimenez@ismsolar.com> wrote:
select var_value from ism_floatvalues where id_signal = 29660 order by time_stamp desc limit 1;
This is what EXPLAIN returns (can't make EXPLAIN ANALYZE because it "never" ends):
"Limit (cost=0.00..258.58 rows=1 width=16)"
" -> Index Scan Backward using ism_floatvalues_index_time_stamp on ism_floatvalues (cost=0.00..8912076.82 rows=34466 width=16)"
" Filter: (id_signal = 29660)"
This is EXPLAIN ANALYZE without "limit 1":
Add (or modify the existing) an index on id_signal, time_stamp desc, and you're done.
It must be a case of descending time stamps not hitting the filter condition (id_signal) soon enough.
