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Re: PostgreSQL - Debian - Processes: postgres: writer process, etc.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-novice(at)postgresql(dot)org
Subject: Re: PostgreSQL - Debian - Processes: postgres: writer process, etc.
Date: 2012-01-30 16:05:10
Message-ID: 15390.1327939510@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-novice
"Jean-Yves F. Barbier" <12ukwn(at)gmail(dot)com> writes:
> On Mon, 30 Jan 2012 02:24:08 -0800 (PST)
> Windybell <lmhelp1(at)orange(dot)fr> wrote:
>> I am wondering what are these four last processes ("postgres: writer",
>> "postgres: wal writer", "postgres: autovacuum launcher" and "postgres: stats
>> collector")?

> Because, as their name suggest it, they take care of Pg different
> parts.

Right.

>> Their PPID is 3069.

> That can't be, each running software/process have a different PID.
> This PID Nb is in the 2nd column.

He said PPID, that is *parent* process ID, so the above is expected ---
they should all be children of the same postmaster process.

>> What is weird to me is the "COMMAND" column as far as these four processes
>> are concerned.
>> In the "COMMAND "column I would expect a real command, not a description.
>> Can you explain?

We intentionally change the command string reported by ps for each
postmaster child process, so that you can tell the various processes
apart.  If we did not, every postmaster child would show the exact
same command string as the postmaster itself was launched with.
(To get an idea of how useless that is, try looking at "top" sometime
--- on most systems I've worked with, it ignores the changed command
strings, so you can't tell what's what.)

			regards, tom lane

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Subject: Re: PostgreSQL - Debian - Processes: postgres: writer process, etc.
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