在一个时间段内以相等的间隔对分钟和最大值执行慢速PostgreSQL查询

我有一个系统，有很多测量设备。这些测量值存储在表“样本数据”中。 每台设备一年可能有1000万次测量。大多数情况下，用户只对某段时间内相同间隔内的100 min-max对感兴趣，例如在过去24小时或过去53周内。为了得到这100分钟和最大值，周期被分成100个相等的间隔。从每个间隔中提取最小值和最大值。您会推荐最有效的数据查询方法吗？到目前为止，我尝试了以下查询：

WITH periods AS (
  SELECT time.start AS st, time.start + (interval '1 year' / 100) AS en
  FROM generate_series(now() - interval '1 year', now(), interval '1 year' / 100) AS time(start)
)
SELECT s.* FROM sample_data s
  JOIN periods ON s.time BETWEEN periods.st AND periods.en 
  JOIN devices d ON d.customer_id = 23
  WHERE
    s.id = (SELECT id FROM sample_data WHERE device_id = d.id and time BETWEEN periods.st AND periods.en ORDER BY sample ASC LIMIT 1) OR
    s.id = (SELECT id FROM sample_data WHERE device_id = d.id and time BETWEEN periods.st     AND periods.en ORDER BY sample DESC LIMIT 1)

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

这个查询花了大约4秒。它不是很合适，因为每个设备的样本_数据表最多可以包含10万行。 我看到它不是以非常优化的方式运行，但不知道为什么。我以为我已经为这个查询中使用的所有关键字段编制了索引

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

你能给我推荐一种更快获取此类统计数据的方法吗

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

表“设备”：

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

它大约有170万行。属于客户的每4台设备约720K行\u id=23。 该表现在由测试数据填充

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

“选择版本（）”结果：

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

轨道io定时设置为“开”

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

在此处解释（分析、缓冲）结果：

---

我猜性能的驱动因素是

where

子句中的查询。让我们看看其中一个：

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

WHERE s.id = (SELECT sd.id
              FROM sample_data sd
              WHERE sd.device_id = d.id and
                    sd.time BETWEEN periods.st AND periods.en
              ORDER BY sd.sample ASC
              LIMIT 1
             ) 

您在

样本数据（设备id、时间、样本）

上有一个索引，您希望数据库引擎使用该索引。不幸的是，它只能对

where

子句充分利用索引。由于之间存在

，因此它可能不会使用

排序依据的索引

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

是否可以使用

时间
通过
写入
订单

       Column       |            Type             |                      Modifiers                       
--------------------+-----------------------------+------------------------------------------------------
 id                 | integer                     | not null default nextval('devices_id_seq'::regclass)
 customer_id        | integer                     | 

    <Other fields skipped as they are not involved into the query>
Indexes:
"devices_pkey" PRIMARY KEY, btree (id)
"index_devices_on_iccid" UNIQUE, btree (iccid)

WHERE s.id = (SELECT id
              FROM sample_data
              WHERE device_id = d.id and
                    time BETWEEN periods.st AND periods.en
              ORDER BY time ASC
              LIMIT 1
             ) 

明白了，谢谢。不幸的是，我不能。“样本”字段用于测量值，我使用它的排序来获得一段时间内的最小值和最大值。@eug.nikolaev。好吧，这确实证明了Postgres会用索引做正确的事情。那么，通过查询获得这种数据是可能的吗？如果没有-看起来我必须在数据插入上准备max mins..Gordon Linoff，谢谢你的解释！决定不在那里使用排序。它（目前）会起作用的。