pg ash自制版 pg_active_session

一、实现功能

由于pgsentinel插件存在严重的内存占用问题，本篇改为自行实现，但其语句仍可以参考pgsentinel插件。PostgreSQL ash —— pgsentinel插件学习与踩坑记录_CSDN博客

v1.0 根据pg 14版本设计及测试，仅支持收集主库信息。默认每10秒收集一次 active与idle in transaction 状态会话信息，保留两个月。

二、历史会话与阻塞信息

参考 pgsentinel插件的pg_active_session_history视图及pg pg_stat_activity视图，根据不同版本，其中部分字段的值可能为空。

pg_ash表

列名	数据类型	字段含义
ash_time	timestamp with time zone	采样时间
datid	oid	会话连接的dbid
datname	name	会话连接的DB名
pid	integer	会话进程ID
leader_pid	integer	并行进程leader id，pg 13新增
usesysid	oid	user id
usename	name	用户名
application_name	text	应用程序名
client_addr	inet	客户端ip
client_hostname	text	客户端主机名
client_port	integer	客户端端口
backend_start	timestamp with time zone	会话连接到服务器的时间
xact_start	timestamp with time zone	当前事务开始的时间，若无活跃事务则为 NULL
query_start	timestamp with time zone	当前活跃查询的开始时间。如果state不为active，则表示上个查询的开始时间
state_change	timestamp with time zone	state上次更改的时间
wait_event_type	text	正在等待的事件类型（如果有）
wait_event	text	正在等待的事件名（如果有）
state	text	当前会话状态
backend_xid	xid	该会话的顶层事务id（如果有）
backend_xmin	xid	该会话的xmin horizon
query	text	active状态下，为当前正在执行的查询；其他状态下，表示最后执行的查询。默认情况下，查询文本被截断为 1024 字节（由参数track_activity_query_size控制）
query_id	bigint	查询id，类似Oracle的sql_id，pg 14新增
backend_type	text	当前会话类型，例如client backend, checkpointer, startup, walreceiver... pg 10新增
blockers	integer	阻塞者数量
blockerpid	integer	阻塞者进程id
blocker_state	text	阻塞者状态

三、表结构创建

1. 按月进行分区

CREATE TABLE public.pg_ash (

ash_time timestamp with time zone,

datid oid,

datname name,

pid integer,

leader_pid integer,

usesysid oid,

usename name,

application_name text,

client_addr inet,

client_hostname text,

client_port integer,

backend_start timestamp with time zone,

xact_start timestamp with time zone,

query_start timestamp with time zone,

state_change timestamp with time zone,

wait_event_type text,

wait_event text,

state text,

backend_xid xid,

backend_xmin xid,

query text,

query_id bigint,

backend_type text,

blockers integer,

blockerpid integer,

blocker_state text

) PARTITION BY RANGE(ash_time);

-- 索引创建

CREATE INDEX idx_pg_ash_n1 ON pg_ash(ash_time);

-- 分区创建，超出最大范围的值会落入默认的final分区

CREATE TABLE pg_ash_history PARTITION OF pg_ash DEFAULT;

CREATE TABLE pg_ash_202310 PARTITION OF pg_ash FOR VALUES FROM ('2023-10-01') TO ('2023-11-01');

CREATE TABLE pg_ash_202311 PARTITION OF pg_ash FOR VALUES FROM ('2023-11-01') TO ('2023-12-01');

CREATE TABLE pg_ash_202312 PARTITION OF pg_ash FOR VALUES FROM ('2023-12-01') TO ('2024-01-01');

2. 定期自动新增分区

3. 自动清理旧分区

四、数据插入

vi pg_ash.sh

#!/bin/bash

. ~/profile << EOF

5432

EOF

psql << EOF

insert into pg_ash

select now(), act.datid, act.datname, act.pid, act.leader_pid, act.usesysid, act.usename,

act.application_name, act.client_addr, act.client_hostname,

act.client_port, act.backend_start, act.xact_start, act.query_start,

act.state_change, act.wait_event_type, act.wait_event, act.state, act.backend_xid,

act.backend_xmin,act.query,act.query_id,act.backend_type,cardinality(pg_blocking_pids(act.pid))

as blockers,(pg_blocking_pids(act.pid))[1] as blockerpid ,blk.state as blocker_state

from pg_stat_activity act left join pg_stat_activity blk

on (pg_blocking_pids(act.pid))[1] = blk.pid

where act.state in ('active', 'idle in transaction') and act.pid != pg_backend_pid();

EOF

五、设置定时执行

由于crontab最小只能按分钟执行，这里利用while true+sleep实现每十秒执行。

vi run.sh 与pg_ash.sh放在相同目录

#!/bin/bash

source .bash_profile

while [ true ]

do

sh ./pg_ash.sh

sleep 10

done

后台运行run.sh

nohup ./run.sh &

六、测试运行效果

1. pgbench压测

初始化数据

-bash-4.2$ createdb pgbench

-bash-4.2$ pgbench -i pgbench

dropping old tables...

NOTICE: table "pgbench_accounts" does not exist, skipping

NOTICE: table "pgbench_branches" does not exist, skipping

NOTICE: table "pgbench_history" does not exist, skipping

NOTICE: table "pgbench_tellers" does not exist, skipping

creating tables...

generating data (client-side)...

100000 of 100000 tuples (100%) done (elapsed 0.23 s, remaining 0.00 s)

vacuuming...

creating primary keys...

done in 0.49 s (drop tables 0.00 s, create tables 0.01 s, client-side generate 0.27 s, vacuum 0.11 s, primary keys 0.10 s).

-bash-4.2$

-bash-4.2$ psql

psql (14.0)

Type "help" for help.

postgres=# \l

List of databases

-----------+----------+----------+------------+------------+-----------------------

| | | | | postgres=CTc/postgres

| | | | | postgres=CTc/postgres

(5 rows)

postgres=# \c pgbench

You are now connected to database "pgbench" as user "postgres".

pgbench=# \d

List of relations

Schema | Name | Type | Owner

--------+------------------+-------+----------

public | pgbench_accounts | table | postgres

public | pgbench_branches | table | postgres

public | pgbench_history | table | postgres

public | pgbench_tellers | table | postgres

(4 rows)

压测脚本

vi test.sql

\set aid random(1, 100000 * :scale)

\set bid random(1, 1 * :scale)

\set tid random(1, 10 * :scale)

\set delta random(-5000, 5000)

BEGIN;

UPDATE pgbench_accounts SET abalance = abalance + :delta WHERE aid = :aid;

SELECT abalance FROM pgbench_accounts WHERE aid = :aid;

UPDATE pgbench_tellers SET tbalance = tbalance + :delta WHERE tid = :tid;

UPDATE pgbench_branches SET bbalance = bbalance + :delta WHERE bid = :bid;

INSERT INTO pgbench_history (tid, bid, aid, delta, mtime) VALUES (:tid, :bid, :aid, :delta, CURRENT_TIMESTAMP);

END;

执行压测

pgbench -c 4 -t 30000 pgbench -r -f test.sql

2. 运行ash脚本

nohup ./run.sh &

3. 查询ash数据

postgres=# select * from pg_ash;

-[ RECORD 1 ]----+-----------------------------------------------------------------------

ash_time | 2023-10-12 05:44:07.152751+08

datid | 41585

datname | pgbench

pid | 1530

leader_pid |

usesysid | 10

usename | postgres

application_name | pgbench

client_addr |

client_hostname |

client_port | -1

backend_start | 2023-10-12 05:44:04.461672+08

xact_start | 2023-10-12 05:44:07.144351+08

query_start | 2023-10-12 05:44:07.145214+08

state_change | 2023-10-12 05:44:07.145215+08

wait_event_type | Lock

wait_event | transactionid

state | active

backend_xid | 677819

backend_xmin | 677814

query | UPDATE pgbench_branches SET bbalance = bbalance + 3177 WHERE bid = 1;

query_id | -6995838559535145041

backend_type | client backend

blockers | 1

blockerpid | 1533

blocker_state | active

-[ RECORD 2 ]----+-----------------------------------------------------------------------

ash_time | 2023-10-12 05:44:07.152751+08

datid | 41585

datname | pgbench

pid | 1531

leader_pid |

usesysid | 10

usename | postgres

application_name | pgbench

client_addr |

client_hostname |

client_port | -1

backend_start | 2023-10-12 05:44:04.463697+08

xact_start | 2023-10-12 05:44:07.151628+08

query_start | 2023-10-12 05:44:07.152311+08

state_change | 2023-10-12 05:44:07.152312+08

wait_event_type | Lock

wait_event | transactionid

state | active

backend_xid | 677821

backend_xmin | 677817

query | UPDATE pgbench_tellers SET tbalance = tbalance + 1637 WHERE tid = 8;

query_id | -9151069917332221911

backend_type | client backend

blockers | 1

blockerpid | 1530

blocker_state | active

...

参考：

PostgreSQL Observability

GitHub - pgsentinel/pgsentinel: postgresql extension providing Active session history