> From: David Rowley <david.rowley@xxxxxxxxxxxxxxx> > Sent: 03 January 2019 14:01 > That's surprisingly slow. Can you share the EXPLAIN (ANALYZE, BUFFERS) of that? > > explain (analyze,buffers) select 'BUIL-B36-VA-RT-RT1:CL0001-2-ABW',c.smpl_time,c.nanosecs,c.float_val,c.num_val,c.str_val,c.datatype,c.array_val from sample c WHERE c.channel_id = (SELECT channel_id FROM channel WHERE name='BUIL-B36-VA-RT-RT1:CL0001-2-ABW') order by c.smpl_time desc limit 5; > -> Index Scan Backward using smpl_time_bx2_idx on sample_buil_year c_5 (cost=0.56..2023925.30 rows=3162364 > width=320) (actual time=15167.330..15167.330 rows=0 loops=1) > Filter: (channel_id = $0) > Rows Removed by Filter: 50597834 > Buffers: shared hit=25913147 read=713221 > -> Index Scan Backward using sample_time_cm_idx on sample_ctrl_month c_6 (cost=0.56..1862587.12 rows=537562 > width=77) (actual time=0.048..0.048 rows=0 loops=1) > Index Cond: (channel_id = $0) > Buffers: shared read=4 > -> Index Scan Backward using smpl_time_cmx2_idx on sample_ctrl_year c_7 (cost=0.57..3186305.67 rows=2094186 > width=68) (actual time=25847.549..25847.549 rows=0 loops=1) > Filter: (channel_id = $0) > Rows Removed by Filter: 79579075 > Buffers: shared hit=49868991 read=1121715 Right, so you need to check your indexes on sample_ctrl_year and sample_buil_year. You need an index on (channel_id, smpl_time) on those. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
