Date: Tue, 24 May 2022 12:40:50 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: =?utf-8?B?5b6Q5b+X5a6H5b6Q?= <xuzhiyuster@gmail.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: How to monitor Postgres real memory usage
Message-ID: <20220524174050.GI19626@telsasoft.com>
References: 
 <CAOCebi+i=HPofBSdvs1RftcZpAHg81R9jqmr5xTJm0dGSDUMNQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: 
 <CAOCebi+i=HPofBSdvs1RftcZpAHg81R9jqmr5xTJm0dGSDUMNQ@mail.gmail.com>
User-Agent: Mutt/1.9.4 (2018-02-28)
Archived-At: 
 <https://www.postgresql.org/message-id/20220524174050.GI19626%40telsasoft.com>
Precedence: bulk

On Wed, May 25, 2022 at 12:25:28AM +0800, 徐志宇徐 wrote:
> Hi All
> 
>   I am a Database DBA. I focus on PostgreSQL and DB2.
>   Recently. I experience some memory issue. The postgres unable allocate
> memory. I don't know how to monitor Postgres memory usage.

Postgres is just an OS Process, so should be monitored like any other.

What OS are you using ?

Know that the OS may attribute "shared buffers" to different processes, or
multiple processes.

>  This server have 16G memory. On that time. The free command display only 3
> G memory used. The share_buffers almost 6G.
> 
>  On that time. The server have 100 active applications.
>  New connection failed. I have to kill some application by os command "kill -9"

It's almost always a bad idea to kill postgres with kill -9.

> The checkpoint command execute very slow. almost need 5-10 seconds.

Do you mean an interactive checkpoint command ?
Or logs from log_checkpoint ?

>   Is there any useful command to summary PostgreSQL memory usage ?

You can check memory use of an individual query with "explain (analyze,buffers) .."
https://wiki.postgresql.org/wiki/Slow_Query_Questions

What settings have you used in postgres ?
https://wiki.postgresql.org/wiki/Server_Configuration

What postgres version ?
How was it installed ?  From souce?  From a package ?

-- 
Justin