Date: Sat, 14 Aug 2021 19:39:08 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: What are exactly bootstrap processes, auxiliary processes,
 standalone backends, normal backends(user sessions)?
Message-ID: <20210815003908.GP10479@telsasoft.com>
References: 
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 <202107171445.v4okkq2xyytm@alvherre.pgsql>
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On Sat, Jul 17, 2021 at 10:45:52AM -0400, Alvaro Herrera wrote:
> On 2021-Jul-17, Bharath Rupireddy wrote:
> > On Thu, Jul 15, 2021 at 8:17 PM Justin Pryzby wrote:
> > > It sounds like something that should be in the glossary, which currently refers
> > > to but doesn't define "auxiliary processes".
> > 
> > Thanks. I strongly feel that it should be documented somewhere. I will
> > be happy if someone with a clear idea about these various processes
> > does it.
> 
> 	Auxiliary process

I elaborated on your definition and added here.
https://commitfest.postgresql.org/34/3285/

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 filename="0001-glossary-definitions-for-auxiliary-processes.patch"

From 9855c0d186251407c868fe0b0d93571541313f55 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj@telsasoft.com>
Date: Sat, 14 Aug 2021 18:51:37 -0500
Subject: [PATCH] glossary definitions for auxiliary processes

---
 doc/src/sgml/glossary.sgml | 58 ++++++++++++++++++++++++++++++++++----
 1 file changed, 53 insertions(+), 5 deletions(-)

diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml
index 63ff4bbdf0..881d16d6c4 100644
--- a/doc/src/sgml/glossary.sgml
+++ b/doc/src/sgml/glossary.sgml
@@ -123,6 +123,27 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-auxiliary">
+   <glossterm>Auxiliary process</glossterm>
+   <glossdef>
+    <para>
+     Process that is in charge of a specific, hardcoded, background task for 
+     an <glossterm linkend="glossary-instance">instance</glossterm>.
+     The auxiliary processes consist of
+<!-- the autovacuum launcher (but not the autovacuum workers), -->
+     the <glossterm linkend="glossary-background-writer">background writer</glossterm>,
+     the <glossterm linkend="glossary-checkpointer">checkpointer</glossterm>,
+     the <glossterm linkend="glossary-stats-collector">statistics collector</glossterm>,
+     the <glossterm linkend="glossary-logger">logger</glossterm>,
+     the <glossterm linkend="glossary-startup-process">startup process</glossterm>,
+     the <glossterm linkend="glossary-wal-archiver">WAL archiver</glossterm>.
+     the <glossterm linkend="glossary-wal-receiver">WAL receiver</glossterm>
+     (but not the WAL senders), and the
+     <glossterm linkend="glossary-wal-writer">WAL writer</glossterm>.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-backend">
    <glossterm>Backend (process)</glossterm>
    <glossdef>
@@ -163,7 +184,7 @@
    <glossterm>Background writer (process)</glossterm>
    <glossdef>
     <para>
-     A process that writes dirty
+     An auxiliary process that writes dirty
      <glossterm linkend="glossary-data-page">data pages</glossterm> from
      <glossterm linkend="glossary-shared-memory">shared memory</glossterm> to
      the file system.  It wakes up periodically, but works only for a short
@@ -285,7 +306,7 @@
    <glossterm>Checkpointer (process)</glossterm>
    <glossdef>
     <para>
-     A specialized process responsible for executing checkpoints.
+     An auxiliary process that is responsible for executing checkpoints.
     </para>
    </glossdef>
   </glossentry>
@@ -881,7 +902,7 @@
    <glossterm>Logger (process)</glossterm>
    <glossdef>
     <para>
-     If activated, the process
+     An auxiliary process which (if enabled)
      writes information about database events into the current
      <glossterm linkend="glossary-log-file">log file</glossterm>.
      When reaching certain time- or
@@ -1452,6 +1473,16 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-startup-process">
+   <glossterm>Startup process</glossterm>
+   <glossdef>
+    <para>
+     An auxiliary process that replays WAL during crash recovery and (on
+     replicas) archive recovery.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry id="glossary-sql-object">
    <glossterm>SQL object</glossterm>
     <glossdef>
@@ -1514,7 +1545,7 @@
    <glossterm>Stats collector (process)</glossterm>
    <glossdef>
     <para>
-     This process collects statistical information about the
+     An auxiliary process that collects statistical information about the
      <glossterm linkend="glossary-instance">instance</glossterm>'s activities.
     </para>
     <para>
@@ -1856,7 +1887,8 @@
    <glossterm>WAL archiver (process)</glossterm>
    <glossdef>
     <para>
-     A process that saves copies of <glossterm linkend="glossary-wal-file">WAL files</glossterm>
+     An auxiliary process that saves copies of
+     <glossterm linkend="glossary-wal-file">WAL files</glossterm>
      for the purpose of creating backups or keeping
      <glossterm linkend="glossary-replica">replicas</glossterm> current.
     </para>
@@ -1914,6 +1946,22 @@
    </glossdef>
   </glossentry>
 
+  <glossentry id="glossary-wal-receiver">
+   <glossterm>WAL receiver</glossterm>
+   <glossdef>
+    <para>
+     An auxiliary process that runs on a
+     <glossterm linkend="glossary-replica">replica</glossterm>
+     to receive and replay WAL from the primary server.
+    </para>
+
+    <para>
+     For more information, see
+     <xref linkend="warm-standby"/>.
+    </para>
+   </glossdef>
+  </glossentry>
+
   <glossentry>
    <glossterm>WAL segment</glossterm>
    <glosssee otherterm="glossary-wal-file" />
-- 
2.17.0


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