我要评论postgresql 查询历史最大进程数方法
postgresql 提供了多种方式来查询数据库的历史最大进程数（连接数）。以下是几种有效的方法：
一 使用统计收集器数据
1.1 查看当前进程信息
select setting as max_connections,
(select setting from pg_settings where name = 'superuser_reserved_connections') as reserved_connections
from pg_settings
where name = 'max_connections';
输出示例：
max_connections | reserved_connections -----------------+---------------------- 100 | 3 (1 row)
1.2 查询历史峰值（需要统计收集器开启）
--当前数据库最大连接数（自统计重置后）
select max(numbackends) as max_connections_ever
from pg_stat_database;
--查看所有数据库最大连接数
select datname,
max(numbackends) as max_connections
from pg_stat_database
group by datname
order by max_connections desc;
输出示例：
white=# select max(numbackends) as max_connections_ever
white-# from pg_stat_database;
max_connections_ever
----------------------
2
(1 row)
white=#
white=# select datname,
white-# max(numbackends) as max_connections
white-# from pg_stat_database
white-# group by datname
white-# order by max_connections desc;
datname | max_connections
-----------+-----------------
white | 2
white3 | 0
white2 | 0
postgres | 0
white1 | 0
template0 | 0
| 0
template1 | 0
(8 rows)
white=#
二 使用 pg_stat_activity 历史快照
2.1 创建扩展记录历史数据
create extension if not exists pg_stat_statements;
create extension if not exists pg_stat_monitor; -- 更高级的监控
-- 创建历史记录表
create table connection_history as
select now() as sample_time,
count(*) as connection_count
from pg_stat_activity;
-- 设置定时任务（如pgagent或cron）定期执行
insert into connection_history
select now(), count(*) from pg_stat_activity;
2.2 查询记录的历史峰值
select max(connection_count) as historical_max_connections
from connection_history;
-- 按时间范围查询
select date_trunc('hour', sample_time) as hour,
max(connection_count) as max_connections_per_hour
from connection_history
where sample_time > now() - interval '7 days'
group by 1
order by 1;
三 使用日志分析
3.1 配置日志记录连接信息
在 postgresql.conf 中设置：
log_connections = on log_disconnections = on log_line_prefix = '%m [%p] %q%u@%d '
3.2 使用pgbadger分析日志
# 生成连接数报告 pgbadger -j 8 /var/log/postgresql/postgresql-*.log -o pgbadger_report.html # 然后查看报告中的"connections"部分
3.3 手动分析日志
# 统计每日最大连接数
grep "connection authorized" /var/log/postgresql/postgresql-15-main.log | \
awk '{print $1}' | \
sort | uniq -c | sort -n
四 使用监控系统数据
4.1 prometheus + grafana
如果使用prometheus监控：
-- 查询过去30天最大连接数 max_over_time(pg_stat_activity_count[30d])
4.2 pgmonitor (crunchy data)
-- 使用预置的监控视图 select * from monitor.pg_connection_history order by max_connections desc limit 10;
五 使用系统视图组合查询
5.1 综合查询方法
with connection_stats as (
select
count(*) as current_connections,
(select setting from pg_settings where name = 'max_connections')::int as max_allowed_connections
from pg_stat_activity
)
select
current_connections,
max_allowed_connections,
round(current_connections * 100.0 / max_allowed_connections, 2) as percentage_used,
(select max(numbackends) from pg_stat_database) as historical_max
from connection_stats;
5.2 跟踪连接变化（需要定期执行）
-- 创建跟踪表 create table if not exists connection_tracking ( ts timestamp primary key, connection_count integer, max_since_reset integer ); -- 更新函数 create or replace function update_connection_stats() returns void as $$ declare current_count integer; historical_max integer; begin select count(*) into current_count from pg_stat_activity; select max(numbackends) into historical_max from pg_stat_database; insert into connection_tracking values (now(), current_count, historical_max) on conflict (ts) do nothing; end; $$ language plpgsql; -- 设置定时执行（如每分钟） -- 可以通过pg_cron扩展或外部cron设置
六 使用 pg_controldata 工具
对于紧急情况分析：
# 查看数据库控制文件信息（包含一些历史统计） pg_controldata /var/lib/postgresql/15/main # 查找以下行： "maximum data alignment: "database block size: "blocks per segment of large relation: "wal block size: "latest checkpoint's maximum connections:"
最佳实践建议
- 长期监控：设置定期记录机制（如每分钟记录连接数）
- 警报阈值：当连接数接近
max_connections的80%时触发警报 - 连接池：考虑使用pgbouncer或pgpool-ii管理连接
- 定期审查：每月分析连接趋势，调整
max_connections参数
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