1

複数のテーブルにデータをクラスター化しましたが、通常は次のようになります。

CREATE TABLE 2012_03_09 (
    guid_key integer,
    property_key integer,
    instance_id_key integer,
    time_stamp timestamp without time zone,
    "value" double precision
)

これらのインデックスで:

CREATE INDEX 2012_03_09_a
  ON 2012_03_09
  USING btree
  (guid_key, property_key, time_stamp);

CREATE INDEX 2012_03_09_b
  ON 2012_03_09
  USING btree
  (time_stamp, property_key);

クエリを分析すると、追加操作の合計時間が気になります。クエリの実行時間が長すぎる理由を教えてください。そのようなクエリを最適化する方法はありますか?

Sort  (cost=262.50..262.61 rows=47 width=20) (actual time=1918.237..1918.246 rows=100 loops=1)    
  Output: 2012_04_26.time_stamp, 2012_04_26.value, 2012_04_26.instance_id_key    
  Sort Key: 2012_04_26.instance_id_key, 2012_04_26.time_stamp    
  Sort Method:  quicksort  Memory: 32kB    
  ->  Append  (cost=0.00..261.19 rows=47 width=20) (actual time=69.817..1917.848 rows=100 loops=1)    
        ->  Index Scan using 2012_04_26_a on 2012_04_26  (cost=0.00..8.28 rows=1 width=20) (actual time=14.909..14.909 rows=0 loops=1)    
              Output: 2012_04_26.time_stamp, 2012_04_26.value, 2012_04_26.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_04_27_a on 2012_04_27  (cost=0.00..8.28 rows=1 width=20) (actual time=1.535..1.535 rows=0 loops=1)    
              Output: 2012_04_27.time_stamp, 2012_04_27.value, 2012_04_27.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_02_a on 2012_05_02  (cost=0.00..12.50 rows=2 width=20) (actual time=53.370..121.894 rows=6 loops=1)    
              Output: 2012_05_02.time_stamp, 2012_05_02.value, 2012_05_02.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_03_a on 2012_05_03  (cost=0.00..24.74 rows=5 width=20) (actual time=59.136..170.215 rows=11 loops=1)    
              Output: 2012_05_03.time_stamp, 2012_05_03.value, 2012_05_03.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_04_a on 2012_05_04  (cost=0.00..12.47 rows=2 width=20) (actual time=67.458..125.172 rows=5 loops=1)    
              Output: 2012_05_04.time_stamp, 2012_05_04.value, 2012_05_04.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_05_a on 2012_05_05  (cost=0.00..8.28 rows=1 width=20) (actual time=14.112..14.112 rows=0 loops=1)    
              Output: 2012_05_05.time_stamp, 2012_05_05.value, 2012_05_05.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_07_a on 2012_05_07  (cost=0.00..12.46 rows=2 width=20) (actual time=60.549..99.999 rows=4 loops=1)    
              Output: 2012_05_07.time_stamp, 2012_05_07.value, 2012_05_07.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_08_a on 2012_05_08  (cost=0.00..24.71 rows=5 width=20) (actual time=63.367..197.296 rows=12 loops=1)    
              Output: 2012_05_08.time_stamp, 2012_05_08.value, 2012_05_08.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_09_a on 2012_05_09  (cost=0.00..28.87 rows=6 width=20) (actual time=59.596..224.685 rows=15 loops=1)    
              Output: 2012_05_09.time_stamp, 2012_05_09.value, 2012_05_09.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_10_a on 2012_05_10  (cost=0.00..28.85 rows=6 width=20) (actual time=56.995..196.590 rows=13 loops=1)    
              Output: 2012_05_10.time_stamp, 2012_05_10.value, 2012_05_10.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_11_a on 2012_05_11  (cost=0.00..20.59 rows=4 width=20) (actual time=62.761..134.313 rows=8 loops=1)    
              Output: 2012_05_11.time_stamp, 2012_05_11.value, 2012_05_11.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_12_a on 2012_05_12  (cost=0.00..8.28 rows=1 width=20) (actual time=12.018..12.018 rows=0 loops=1)    
              Output: 2012_05_12.time_stamp, 2012_05_12.value, 2012_05_12.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_13_a on 2012_05_13  (cost=0.00..8.28 rows=1 width=20) (actual time=12.286..12.286 rows=0 loops=1)    
              Output: 2012_05_13.time_stamp, 2012_05_13.value, 2012_05_13.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_14_a on 2012_05_14  (cost=0.00..16.58 rows=3 width=20) (actual time=92.161..156.802 rows=6 loops=1)    
              Output: 2012_05_14.time_stamp, 2012_05_14.value, 2012_05_14.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_15_a on 2012_05_15  (cost=0.00..25.03 rows=5 width=20) (actual time=73.636..263.537 rows=14 loops=1)    
              Output: 2012_05_15.time_stamp, 2012_05_15.value, 2012_05_15.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
        ->  Index Scan using 2012_05_16_a on 2012_05_16  (cost=0.00..12.56 rows=2 width=20) (actual time=100.893..172.404 rows=6 loops=1)    
              Output: 2012_05_16.time_stamp, 2012_05_16.value, 2012_05_16.instance_id_key    
              Index Cond: ((guid_key = 2105) AND (property_key = 67) AND (time_stamp >= '2012-04-16 00:00:00'::timestamp without time zone) AND (time_stamp <= '2012-05-16 06:25:50.172'::timestamp without time zone))    
Total runtime: 1918.745 ms

アップデート：

SQLクエリも投稿：

select time_stamp, value, instance_id_key as segment from perf_hourly_2012_04_26 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_04_27 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_02 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_03 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_04 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_05 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_07 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_08 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_09 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_10 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_11 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_12 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_13 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_14 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_15 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
UNION ALL
select time_stamp, value, instance_id_key as segment from 2012_05_16 where guid_key = 2105 and property_key=67 and time_stamp between '2012-04-16 00:00:00.0'::timestamp without time zone and '2012-05-16 06:25:50.172'::timestamp without time zone
ORDER BY 3 ASC, 1 ASC
4

3 に答える 3

1

UNION はタイミングの問題ではなく、報告された経過時間は基本的に各パーティションのインデックス スキャン時間の合計です。_a インデックスは、クエリ述語に対して適切に選択されているようです。Explain Analyst で見たリアルタイムの原因は、各パーティションのインデックス スキャンで数行を取得するのに時間がかかっていることです。例: 2012_05_04 の 5 行で 125 ミリ秒。インデックス スキャンは、キャッシュの状態とテーブルのサイズに応じて 0 ～ 5 回のシークを呼び出す必要があります。データがクラスター化されていない場合は、データ行ごとに 1 回のシークが発生します。低速のシングル スピンドル ディスクはシークとブロック フェッチを最大 10 ミリ秒で実行できるはずです。そのため、粗悪なストレージ システムでのスキャンの最悪のケースは約 100 ミリ秒ですが、より一般的な 7200 または 10K rpm ディスクと複数のスピンドルでは、最悪の場合です。キャッシュ ヒットが 50 ミリ秒未満であると仮定した場合。

このクエリは、最初の試行の直後に 2 回目の試行を行うと、より高速に実行されますか? もしそうなら、それは問題としてコールドキャッシュによる遅いストレージを示しています. データベースはどのような種類のストレージで実行されていますか? 遅いラップトップ ドライブや高レイテンシーのネットワーク マウントについて話している場合は、IO パフォーマンスが低いことを説明できます。インデックス スキャンは、極端なインデックスの肥大化によっても影響を受ける可能性があります。不適切なバキューム レジメンによるデータの更新/削除チャーンが原因で、数十または数百のデッド インデックス エントリがある場合、それが原因である可能性があります。これらのテーブルは定期的にバキュームされ、分析されていますか?

Adrian Serafin が提案したように、Pg のテーブル分割機能を調べる必要があります。

于 2012-05-17T18:18:14.127 に答える