Postgres查询需要很长时间

Question

I have this SQL query which takes long time (~12s) to execute:

select nextval('rec_id_seq_af') as rec_id,ds_id,ds_dt_id,
inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq from rs_data_1_af 
group by ds_id,ds_dt_id,inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq 
order by ds_id,ds_dt_id,inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq;

When I run:

EXPLAIN (ANALYZE, BUFFERS)
select nextval('rec_id_seq_af') as rec_id,ds_id,ds_dt_id,
inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq from rs_data_1_af 
group by ds_id,ds_dt_id,inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq 
order by ds_id,ds_dt_id,inv_vcf_id,inv_sample_id,inv_variant_id,ds_dt_line_seq;

This is the output:

Group  (cost=724728.48..780477.07 rows=314077 width=88) (actual time=10395.641..12546.322 rows=5703 loops=1)
  Group Key: ds_id, ds_dt_id, inv_vcf_id, inv_sample_id, inv_variant_id, ds_dt_line_seq
  Buffers: shared hit=80975, temp read=91041 written=91171
  ->  Sort  (cost=724728.48..732580.39 rows=3140766 width=80) (actual time=10395.619..12019.351 rows=3140766 loops=1)
        Sort Key: ds_id, ds_dt_id, inv_vcf_id, inv_sample_id, inv_variant_id, ds_dt_line_seq
        Sort Method: external merge  Disk: 286312kB
        Buffers: shared hit=75272, temp read=91041 written=91171
        ->  Seq Scan on rs_data_1_af  (cost=0.00..106679.66 rows=3140766 width=80) (actual time=0.009..575.729 rows=3140766 loops=1)
              Buffers: shared hit=75272
Planning Time: 0.478 ms
Execution Time: 12581.964 ms

When the records in rs_data_1_af table increases, I would have million of rows, this query takes hours to execute.

How can I optimize?

Answer 1

Why are you running nextval('rec_id_seq_af') ?

nextval() advances the index and returns the next value. For each row it has to do that, read/write in isolation, no wonder it is slow.

What is the purpose there, perhaps you can use generate_series() or something else?