How to get the free disk space in PostgreSQL (PostgreSQL获取磁盘空间)

Get the current free disk space in PostgreSQL

PostgreSQL获取磁盘空间

Here has a simple way to get free disk space without any extended language, just define a function using pgsql.

CREATE OR REPLACE FUNCTION sys_df() RETURNS SETOF text[]
LANGUAGE plpgsql $$
BEGIN
    CREATE TEMP TABLE IF NOT EXISTS tmp_sys_df (content text) ON COMMIT DROP;
    COPY tmp_sys_df FROM PROGRAM 'df | tail -n +2';
    RETURN QUERY SELECT regexp_split_to_array(content, '\s+') FROM tmp_sys_df;
END;
$$;

Usage:

select * from sys_df();
                      sys_df                               
-------------------------------------------------------------------
 {overlay,15148428,6660248,7695656,46%,/}
 {overlay,15148428,6660248,7695656,46%,/}
 {tmpfs,65536,0,65536,0%,/dev}
 {tmpfs,768284,0,768284,0%,/sys/fs/cgroup}
 {/dev/sda2,15148428,6660248,7695656,46%,/etc/resolv.conf}
 {/dev/sda2,15148428,6660248,7695656,46%,/etc/hostname}
 {/dev/sda2,15148428,6660248,7695656,46%,/etc/hosts}
 {shm,65536,8,65528,0%,/dev/shm}
 {/dev/sda2,15148428,6660248,7695656,46%,/var/lib/postgresql/data}
 {tmpfs,65536,0,65536,0%,/proc/kcore}
 {tmpfs,65536,0,65536,0%,/proc/timer_list}
 {tmpfs,65536,0,65536,0%,/proc/sched_debug}
 {tmpfs,768284,0,768284,0%,/sys/firmware}
(13 rows)

Using df $PGDATA | tail -n +2 instead of df | tail -n +2 while you saving all data in same path on disk. In this case, the function only return one row disk usage for $PGDATA path.

NOTE FOR SECURITY

PROGRAM can run any command by shell, it like two-edged sword. it is best to use a fixed command string, or at least avoid passing any user input in it. See detail on document.

PROGRAM可以运行任意的命令，所以最好是用固定字符串命令，尽量避免通过参数传入。