慢Query日志查看与分析

在Hologres中查询慢Query日志，具体限制如下：

• 慢Query日志默认保留一个月的数据，但是HoloWeb仅支持查最近7天的数据，如果需要查询一个月内的数据请使用SQL进行查询。

• 为了保证系统稳定性，避免流量超载，单次查询最多返回10000条慢Query日志。慢Query日志中的部分字段有长度限制，详情请参见query_log表字段说明。

• 慢Query日志属于Hologres的元仓系统，慢Query日志查询失败不会影响实例中的业务Query运行，故慢Query日志的稳定性不在产品的SLA保护范围内。

Hologres的慢Query查询日志存储于hologres.hg_query_log系统表中，其中：

• 在实例升级至V0.10版本后，将会默认采集执行时间大于100 ms的慢DML Query以及所有的DDL操作。

• 自V3.0.2版本开始，支持在原有的hologres.hg_query_log中，使用聚合方式记录执行时间小于100 ms的DML和查询的记录。

  • 系统会将执行时间小于100 ms，成功且有指纹的Query（DQL和DML）操作进行聚合记录。

  • 聚合的主要列为：server_addr、usename、datname、warehouse_id、application_name、digest。

  • 每个连接每分钟会汇总一次后上报。

hologres.hg_query_log系统表，包含的字段信息介绍如下。

您可以通过HoloWeb可视化查看慢Query日志。

您可以通过查询hologres.hg_query_log表，获取慢Query日志。如下将为您介绍进行Query日志诊断常用的固定SQL语句。主要包括：

• 查询query_log总查询数

• 查询每个用户的慢Query情况

• 查询某个慢Query的具体信息

• 查询最近10分钟消耗比较高的Query

• 查看最近3小时内每小时的Query访问量和数据读取总量

• 查看与昨天同一时间对比过去3小时的数据访问量情况

• 查询最近10分钟Query各阶段耗时比较高的Query

• 查询最先失败的Query

• 查询query_log总查询数（默认为近1个月内的数据）。

  SELECT count(*) FROM hologres.hg_query_log;

  执行结果如下，表示近1个月内总共执行了44个耗时大于指定阈值的Query。

  count
  -------
      44
  (1 row)

• 查询每个用户的慢Query个数。

  SELECT usename AS "用户",
         count(1) as "Query个数"
  FROM hologres.hg_query_log
  GROUP BY usename
  order by count(1) desc;

  执行结果如下，其中count(1)的单位是个数。

  用户                   | Query个数
  -----------------------+-----
   1111111111111111      |  27
   2222222222222222      |  11
   3333333333333333      |   4
   4444444444444444      |   2
  (4 rows)

• 查询某个慢Query的具体信息。

  SELECT * FROM hologres.hg_query_log WHERE query_id = '13001450118416xxxx';

  执行结果如下，更多关于各参数的说明，请参见查看query_log表。

         usename      | status  |      query_id      | datname| command_tag | duration | message |      query_start       | query_date |                                             query                                                  | result_rows | result_bytes | read_rows |read_bytes | affected_rows | affected_bytes | memory_bytes | shuffle_bytes | cpu_time_ms | physical_reads |   pid   | application_name | engine_type |  client_addr  | table_write | table_read |   session_id   |     session_start      | command_id | optimization_cost | start_query_cost | get_next_cost | extended_cost | plan | statistics | visualization_info | query_detail | query_extinfo
  -----------------------+---------+--------------------+---------+-------------+----------+---------+------------------------+------------+---------------------------------------------------------------------------------------------------------+-------------+--------------+-----------+------------+---------------+----------------+--------------+---------------+-------------+----------------+---------+------------------+-------------+---------------+-------------+------------+-----------------+------------------------+------------+-------------------+------------------+---------------+---------------+------+------------+--------------------+--------------+---------------
   p4_11111111111xxxx | SUCCESS | 13001450118416xxxx | dbname | SELECT      |      149 |         | 2021-03-30 23:45:01+08 | 20210330   | explain analyze SELECT  * FROM tablename WHERE user_id = '20210330010xxxx' limit 1000;             |        1000 |       417172 |         0 |         0 |            -1 |             -1 |     26731376 |     476603616 |      321626 |              0 | 1984913 | psql             | {HQE}      | 33.41.xxx.xxx |             |            | 6063475a.1e4991 | 2021-03-30 23:44:26+08 | 0          |                58 |               22 |            67 |               |      |            |                    |              |
  (1 row)

• 查询最近某个时间段（如10分钟）消耗比较高的Query。您也可以根据业务需求修改具体时间，查询目标时间段消耗比较高的Query。

  SELECT status AS "状态",
         duration AS "耗时(ms)",
         query_start AS "开始时间",
         (read_bytes/1048576)::text || ' MB' AS "读取量",
         (memory_bytes/1048576)::text || ' MB' AS "内存",
         (shuffle_bytes/1048576)::text || ' MB' AS "Shuffle",
         (cpu_time_ms/1000)::text || ' s' AS "CPU时间",
         physical_reads as "读盘",
         query_id as "QueryID",
         query::char(30)
   FROM hologres.hg_query_log
   WHERE query_start >= now() - interval '10 min'
   ORDER BY duration DESC,
            read_bytes DESC,
            shuffle_bytes DESC,
            memory_bytes DESC,
            cpu_time_ms DESC,
            physical_reads DESC
  LIMIT 100;

  执行结果如下：

  状态     |耗时(ms) |    开始时间            | 读取量 | 内存  | Shuffle | CPU时间 | 读盘 |      QueryID       |             query
  ---------+---------+------------------------+--------+-------+---------+---------+------+--------------------+--------------------------------
   SUCCESS |  149    | 2021-03-30 23:45:01+08 | 0 MB   | 25 MB | 454 MB  | 321 s   |    0 | 13001450118416xxxx | explain analyze SELECT  * FROM
   SUCCESS |  137    | 2021-03-30 23:49:18+08 | 247 MB | 21 MB | 213 MB  | 803 s   | 7771 | 13001491818416xxxx | explain analyze SELECT  * FROM
   FAILED  |   53    | 2021-03-30 23:48:43+08 | 0 MB   | 0 MB  | 0 MB    | 0 s     |    0 | 13001484318416xxxx | SELECT ds::bigint / 0 FROM pub
  (3 rows)

• 查看昨日新增的Query数量。

  • 统计昨日新增的Query总量。

    SELECT
        COUNT(1)
    FROM ( SELECT DISTINCT
            t1.digest
        FROM
            hologres.hg_query_log t1
        WHERE
            t1.query_start >= CURRENT_DATE - INTERVAL '1 day'
            AND t1.query_start < CURRENT_DATE
            AND NOT EXISTS (
                SELECT
                    1
                FROM
                    hologres.hg_query_log t2
                WHERE
                    t2.digest = t1.digest
                    AND t2.query_start < CURRENT_DATE - INTERVAL '1 day')
            AND digest IS NOT NULL
     ) AS a;

    执行结果如下，表示昨日新增Query总量为10个。

    count  
    -------
        10 
    (1 row)

  • 按照查询的类型（command_tag）分组统计昨日新增的Query数量。

    SELECT
        a.command_tag,
        COUNT(1)
    FROM ( SELECT DISTINCT
            t1.digest,
            t1.command_tag
        FROM
            hologres.hg_query_log t1
        WHERE
            t1.query_start >= CURRENT_DATE - INTERVAL '1 day'
            AND t1.query_start < CURRENT_DATE
            AND NOT EXISTS (
                SELECT
                    1
                FROM
                    hologres.hg_query_log t2
                WHERE
                    t2.digest = t1.digest
                    AND t2.query_start < CURRENT_DATE - INTERVAL '1 day')
                AND t1.digest IS NOT NULL) AS a
    GROUP BY
        1
    ORDER BY
        2 DESC;

    执行结果如下，表示昨日新增8个INSERT和2个SELECT类型的Query。

    command_tag	| count  
    ------------+--------
    INSERT	    |    8   
    SELECT	    |    2
    (2 rows)

• 查看昨日新增的Query明细。

  SELECT
      a.usename,
      a.status,
      a.query_id,
      a.digest, 
      a.datname,
      a.command_tag,
      a.query,
      a.cpu_time_ms,
      a.memory_bytes
  FROM (
      SELECT DISTINCT
          t1.usename,
          t1.status,
          t1.query_id,
          t1.digest, 
          t1.datname,
          t1.command_tag,
          t1.query,
          t1.cpu_time_ms,
          t1.memory_bytes
      FROM
          hologres.hg_query_log t1
      WHERE
           t1.query_start >= CURRENT_DATE - INTERVAL '1 day' 
          AND t1.query_start < CURRENT_DATE 
          AND NOT EXISTS (
              SELECT
                  1
              FROM
                  hologres.hg_query_log t2
              WHERE
                  t2.digest = t1.digest
                  AND t2.query_start < CURRENT_DATE - INTERVAL '1 day'
          )
          AND t1.digest IS NOT NULL
  ) AS a; 

  执行结果如下：

  usename	         |status  |query_id	           |digest	                            |datname|command_tag	|query	                            |cpu_time_ms   |memory_bytes
  -----------------+--------+--------------------+------------------------------------+-------+-------------+-----------------------------------+--------------+--------------
  111111111111xxxx |SUCCESS |100100425827776xxxx |md58cf93d91c36c6bc9998add971458ba1a |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  | 	   		 1748|	   898808596
  111111111111xxxx |SUCCESS |100100425827965xxxx |md5f7e87e2c9e0b3d9eddcd6b3bc7f04b3b |dbname	|INSERT       |INSERT INTO xxx SELECT * FROM xxx  | 	   		59891|	  6819529886
  111111111111xxxx |SUCCESS |100100425829654xxxx |md55612dc09d2d81074fd5deed1aa3eca9b |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |   	   		  3|	     2100039
  111111111111xxxx |SUCCESS |100100425829664xxxx |md58d3bf67fbdf2247559bc916586d40011 |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |     		10729|	  2052861937
  111111111111xxxx |SUCCESS |100100425830099xxxx |md503bd45d6b2d7701c2617d079b4d55a10 |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |	   		   2196|     897948034
  111111111111xxxx |SUCCESS |100100425830186xxxx |md5c62169eaf3ea3a0c59bdc834a8141ac4 |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |	   		   5268|    1734305972
  111111111111xxxx |SUCCESS |100100425830448xxxx |md59aa0c73b24c9c9eba0b34c8fdfc23bb0 |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |	   		      2|       2098402
  111111111111xxxx |SUCCESS |100100425830459xxxx |md57d22c1d37b68984e9472f11a4c9fd04e |dbname	|INSERT	      |INSERT INTO xxx SELECT * FROM xxx  |	   		    113|      76201984
  111111111111xxxx |SUCCESS |100100525468694xxxx |md5ac7d6556fae123e9ea9527d8f1c94b1c |dbname	|SELECT	      |SELECT * FROM xxx limit 200	      |     		    6|	     1048576
  111111111111xxxx |SUCCESS |100101025538840xxxx |md547d09cdad4d5b5da74abaf08cba79ca0 |dbname	|SELECT	      |SELECT * FROM xxx limit 200	      |\N	           |\N        
  (10 rows)

• 查看昨日新增的Query趋势（按小时展示）。

  SELECT
      to_char(a.query_start, 'HH24') AS query_start_hour,
      a.command_tag,
      COUNT(1)
  FROM (
      SELECT DISTINCT
          t1.query_start,
          t1.digest,
          t1.command_tag
      FROM
          hologres.hg_query_log t1
      WHERE
           t1.query_start >= CURRENT_DATE - INTERVAL '1 day' 
           AND t1.query_start < CURRENT_DATE 
           AND NOT EXISTS (
              SELECT
                  1
              FROM
                  hologres.hg_query_log t2
              WHERE
                  t2.digest = t1.digest
                  AND t2.query_start < CURRENT_DATE - INTERVAL '1 day'
           )
           AND t1.digest IS NOT NULL
  ) AS a 
  GROUP BY 1, 2
  ORDER BY 
  	3 DESC; 

  执行结果如下，表示在昨日的11时、13时、21时分别新增了1个SELECT、1个SELECT、8个INSERT类型的Query。

  query_start_hour	|command_tag	|count
  ------------------+-------------+-----
  	            21	|INSERT	      |    8
  	            11	|SELECT	      |    1
  	            13	|SELECT	      |    1
  (3 rows)

• 归类慢Query的次数。

  SELECT
      digest,
      command_tag,
      count(1)
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= CURRENT_DATE - INTERVAL '1 day'
      AND query_start < CURRENT_DATE
  GROUP BY
      1,2
  ORDER BY
      3 DESC;

• 查询过去1天CPU平均耗时前十的Query。

  SELECT
      digest,
      avg(cpu_time_ms)
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= CURRENT_DATE - INTERVAL '1 day'
      AND query_start < CURRENT_DATE
      AND digest IS NOT NULL
      AND usename != 'system'
      AND cpu_time_ms IS NOT NULL
  GROUP BY
      1
  ORDER BY
      2 DESC
  LIMIT 10;

• 查看过去一周内存（memory_bytes）平均消耗量前十的Query。

  SELECT
      digest,
      avg(memory_bytes)
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= CURRENT_DATE - INTERVAL '7 day'
      AND query_start < CURRENT_DATE
      AND digest IS NOT NULL
      AND memory_bytes IS NOT NULL
  GROUP BY
      1
  ORDER BY
      2 DESC
  LIMIT 10;

• 查看最近3小时内每小时的Query访问量和数据读取总量，用于对比判断每个小时是否有数据量变化。

  SELECT
      date_trunc('hour', query_start) AS query_start,
      count(1) AS query_count,
      sum(read_bytes) AS read_bytes,
      sum(cpu_time_ms) AS cpu_time_ms
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= now() - interval '3 h'
  GROUP BY 1;

• 查看与昨天同一时间对比过去3小时的数据访问量情况，用于判断相较于昨日是否有数据量访问变化。

  SELECT
      query_date,
      count(1) AS query_count,
      sum(read_bytes) AS read_bytes,
      sum(cpu_time_ms) AS cpu_time_ms
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= now() - interval '3 h'
  GROUP BY
      query_date
  UNION ALL
  SELECT
      query_date,
      count(1) AS query_count,
      sum(read_bytes) AS read_bytes,
      sum(cpu_time_ms) AS cpu_time_ms
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= now() - interval '1d 3h'
      AND query_start <= now() - interval '1d'
  GROUP BY
      query_date;

• 查询最近时间段（如最近10分钟）Query各阶段耗时比较高的Query。您也可以根据业务需求修改具体时间，查询目标时间段Query各阶段耗时比较高的Query。

  SELECT
      status AS "状态",
      duration AS "耗时(ms)",
      optimization_cost AS "优化耗时(ms)",
      start_query_cost AS "启动耗时(ms)",
      get_next_cost AS "执行耗时(ms)",
      duration - optimization_cost - start_query_cost - get_next_cost AS "其他耗时(ms)",
      query_id AS "QueryID",
      query::char(30)
  FROM
      hologres.hg_query_log
  WHERE
      query_start >= now() - interval '10 min'
  ORDER BY
      duration DESC,
      start_query_cost DESC,
      optimization_cost,
      get_next_cost DESC,
      duration - optimization_cost - start_query_cost - get_next_cost DESC
  LIMIT 100;

  执行结果如下：

  状态     | 耗时(ms) | 优化耗时(ms) | 启动耗时(ms) | 执行耗时(ms) | 其他耗时(ms) |      QueryID       |             query
  ---------+----------+--------------+--------------+--------------+--------------+--------------------+--------------------------------
   SUCCESS |     4572 |          521 |          320 |         3726 |            5 | 6000260625679xxxx  | -- /* user: wang ip: xxx.xx.x
   SUCCESS |     1490 |          538 |           98 |          846 |            8 | 12000250867886xxxx | -- /* user: lisa ip: xxx.xx.x
   SUCCESS |     1230 |          502 |           95 |          625 |            8 | 26000512070295xxxx | -- /* user: zhang ip: xxx.xx.
  (3 rows)

• 查询最先失败的Query。

  SELECT
      status AS "状态",
      regexp_replace(message, '\n', ' ')::char(150) AS "报错信息",
      duration AS "耗时(ms)",
      query_start AS "开始时间",
      query_id AS "QueryID",
      query::char(100) AS "Query"
  FROM
      hologres.hg_query_log
  WHERE
      query_start BETWEEN '2021-03-25 17:00:00'::timestamptz AND '2021-03-25 17:42:00'::timestamptz + interval '2 min'
      AND status = 'FAILED'
  ORDER BY
      query_start ASC
  LIMIT 100;

  执行结果如下：

  状态    |                                                                     报错信息                                                                           | 耗时(ms)  |        开始时间        |     QueryID       | Query
  --------+--------------------------------------------------------------------------------------------------------------------------------------------------------+-------+------------------------+-------------------+-------
   FAILED | Query:[1070285448673xxxx] code: kActorInvokeError msg: "[holo_query_executor.cc:330 operator()] HGERR_code XX000 HGERR_msge internal error: status { c |  1460 | 2021-03-25 17:28:54+08 | 1070285448673xxxx | S...
   FAILED | Query:[1016285560553xxxx] code: kActorInvokeError msg: "[holo_query_executor.cc:330 operator()] HGERR_code XX000 HGERR_msge internal error: status { c |   131 | 2021-03-25 17:28:55+08 | 1016285560553xxxx | S...
  (2 rows)