Postgres查詢需要很長時間

Question

我有這個 SQL 查詢需要很長時間（~12s）才能執行：

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;

當我運行時：

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;

這是 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

當 rs_data_1_af 表中的記錄增加時，我會有數百萬行，這個查詢需要幾個小時才能執行。

我該如何優化？

Answer 1

你為什么要運行nextval('rec_id_seq_af') ？

nextval()推進索引並返回下一個值。 對於每一行，它必須這樣做，獨立地讀/寫，難怪它很慢。

那里的目的是什么，也許您可以使用generate_series()或其他東西？