Question

我有一个大的（近10M记录）数据表，出于性能原因，它有一个辅助聚合伴随表。聚合表定期填充sofar unaggregated数据：

REPLACE INTO aggregate (channel_id, type, timestamp, value, count)
SELECT channel_id, 'day' AS type, MAX(timestamp) AS timestamp, SUM(value) AS value, COUNT(timestamp) AS count FROM data 
WHERE timestamp < UNIX_TIMESTAMP(DATE_FORMAT(NOW(), "%Y-%m-%d")) * 1000 
AND timestamp >= IFNULL((SELECT UNIX_TIMESTAMP(DATE_ADD(FROM_UNIXTIME(MAX(timestamp)/1000, "%Y-%m-%d"), 
    INTERVAL 1 day)) * 1000 FROM aggregate WHERE type = 'day'), 0) 
GROUP BY channel_id, YEAR(FROM_UNIXTIME(timestamp/1000)), DAYOFYEAR(FROM_UNIXTIME(timestamp/1000));

我发现语句的SELECT部分非常慢（快速PC上2秒以上），即使没有返回数据也是如此。由于聚合需要在嵌入式设备上运行，因此这是一个问题。这是计划：

id  select_type table       type        key     key_len rows    Extra
1   PRIMARY     data        ALL                         9184560 Using where; Using temporary; Using filesort
2   SUBQUERY    aggregate   index       ts_uniq 22      1940    Using where; Using index

子查询本身是即时的。由于data子句中的计算，显然channel_id/timestamp不使用GROUP BY索引：

CREATE TABLE `data` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `channel_id` int(11) DEFAULT NULL,
  `timestamp` bigint(20) NOT NULL,
  `value` double NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `ts_uniq` (`channel_id`,`timestamp`),
  KEY `IDX_ADF3F36372F5A1AA` (`channel_id`)
) ENGINE=MyISAM AUTO_INCREMENT=10432870 DEFAULT CHARSET=latin1;

可以进一步优化查询吗？

更新：添加所需信息

SHOW INDEXES FROM data;

Table   Non_unique  Key_name    Seq_in_index    Column_name Collation   Cardinality Null    Index_type
data    0           PRIMARY     1               id          A           9184560             BTREE       
data    0           ts_uniq     1               channel_id  A           164         YES     BTREE       
data    0           ts_uniq     2               timestamp   A           9184560             BTREE       
data    1           IDX_ADF3..  1               channel_id  A           164         YES     BTREE       

CREATE TABLE `aggregate` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `channel_id` int(11) NOT NULL,
  `type` varchar(8) NOT NULL,
  `timestamp` bigint(20) NOT NULL,
  `value` double NOT NULL,
  `count` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `ts_uniq` (`channel_id`,`type`,`timestamp`)
) ENGINE=MyISAM AUTO_INCREMENT=1941 DEFAULT CHARSET=latin1;

我还注意到，当将GROUP BY更改为channel_id时间戳时，查询会立即生效。不幸的是，将数据计算添加为列是不可取的，因为分组是动态计算的。

当我甚至没有任何要分组的数据时，我无法理解为什么GROUP BY索引应该是一个问题。我试过了

SELECT channel_id, 'day' AS type, MAX(timestamp) AS timestamp, SUM(value) AS value, COUNT(timestamp) AS count FROM data 
WHERE timestamp < UNIX_TIMESTAMP(DATE_FORMAT(NOW(), "%Y-%m-%d")) * 1000 
AND timestamp >= IFNULL((SELECT UNIX_TIMESTAMP(DATE_ADD(FROM_UNIXTIME(MAX(timestamp)/1000, "%Y-%m-%d"), INTERVAL 1 day)) * 1000 
    FROM aggregate WHERE type = 'day'), 0)

这同样慢，所以GROUP似乎不是问题吗？

更新2

进一步向下挖掘道路

SELECT channel_id, 'day' AS type, timestamp, value, 1 FROM data 
WHERE timestamp >= (SELECT UNIX_TIMESTAMP(DATE_ADD(FROM_UNIXTIME(MAX(timestamp)/1000, "%Y-%m-%d"), 
    INTERVAL 1 day)) * 1000 FROM aggregate WHERE type = 'day');

仍然很慢（1.4秒） - 所以根本不是GROUP BY问题。

更新3

这仍然很慢：

SELECT channel_id, 'day' AS type, timestamp, value, 1 FROM data WHERE timestamp >= 1380837600000;

所以 - 问题是内部比较是针对时间戳的，它不能使用channel_id，timestamp索引，尽管这是GROUP BY子句的一部分。这导致了如何强制该指数的问题？

Answer 1

将年和年日列添加到数据表，并在（channel_id，year，dayofyear）上设置索引。插入行时填充两个新列。

如何在计算字段上优化GROUP BY（使用索引）？

1 个答案: