<glossterm>Analyze (operation)</glossterm>

<glossdef>

<para>

Theprocess of collecting statistics from data in

Theact of collecting statistics from data in

<glossterm linkend="glossary-table">tables</glossterm>

and other <glossterm linkend="glossary-relation">relations</glossterm>

to help the <glossterm linkend="glossary-planner">query planner</glossterm>

<para>

A set of background processes that routinely perform

<glossterm linkend="glossary-vacuum">vacuum</glossterm>

and <glossterm linkend="glossary-analyze">analyze</glossterm>

operations.

and <glossterm linkend="glossary-analyze">analyze</glossterm> operations.

The <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

that coordinates the work and is always present (unless autovacuum

is disabled) is known as the <firstterm>autovacuum launcher</firstterm>,

and the processes that carry out the tasks are known as the

<firstterm>autovacuum workers</firstterm>.

</para>

<para>

For more information, see

</glossdef>

</glossentry>

<glossentry id="glossary-auxiliary-proc">

<glossterm>Auxiliary process</glossterm>

<glossdef>

<para>

A process within an <glossterm linkend="glossary-instance">instance</glossterm>

that is in charge of some specific background task for the instance.

The auxiliary processes consist of <!-- in alphabetical order -->

<!-- NB: In the code, the autovac launcher doesn't use the auxiliary

process scaffolding; however it does behave as one so we list it

here anyway. In addition, logger and stats collector aren't

connected to shared memory so most code outside postmaster.c

doesn't even consider them "procs" in the first place.

-->

the <glossterm linkend="glossary-autovacuum">autovacuum launcher</glossterm>

(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-logger">logger</glossterm>,

the <glossterm linkend="glossary-startup-process">startup process</glossterm>,

the <glossterm linkend="glossary-stats-collector">statistics collector</glossterm>,

the <glossterm linkend="glossary-wal-archiver">WAL archiver</glossterm>,

the <glossterm linkend="glossary-wal-receiver">WAL receiver</glossterm>

(but not the <glossterm linkend="glossary-wal-sender">WAL senders</glossterm>),

and the <glossterm linkend="glossary-wal-writer">WAL writer</glossterm>.

</para>

</glossdef>

</glossentry>

<glossentry id="glossary-backend">

<glossterm>Backend (process)</glossterm>

<glossdef>

<glossterm>Background writer (process)</glossterm>

<glossdef>

<para>

A process that writes dirty

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

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

<glossterm>Checkpointer (process)</glossterm>

<glossdef>

<para>

A specialized process responsible for executing checkpoints.

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

that is responsible for executing

<glossterm linkend="glossary-checkpoint">checkpoints</glossterm>.

</para>

</glossdef>

</glossentry>

<glossterm>Instance</glossterm>

<glossdef>

<para>

A group of backend and auxiliary processes that communicate using

a common shared memory area. One

A group of <glossterm linkend="glossary-backend">backend</glossterm> and

<glossterm linkend="glossary-auxiliary-proc">auxiliary processes</glossterm>

that communicate using a common shared memory area. One

<glossterm linkend="glossary-postmaster">postmaster process</glossterm>

manages the instance; one instance manages exactly one

<glossterm linkend="glossary-db-cluster">database cluster</glossterm>

<glossterm>Logger (process)</glossterm>

<glossdef>

<para>

If activated, the process

writes information about database events into the current

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

which, if enabled,writes information about database events into the current

<glossterm linkend="glossary-log-file">log file</glossterm>.

When reaching certain time- or

volume-dependent criteria, a new log file is created.

<glossdef>

<para>

The very first process of an <glossterm linkend="glossary-instance">instance</glossterm>.

It starts and manages the other auxiliary processes and creates

<glossterm linkend="glossary-backend">backend processes</glossterm>

It starts and manages the

<glossterm linkend="glossary-auxiliary-proc">auxiliary processes</glossterm>

and creates <glossterm linkend="glossary-backend">backend processes</glossterm>

on demand.

</para>

<para>

</glossdef>

</glossentry>

<glossentry id="glossary-startup-process">

<glossterm>Startup process</glossterm>

<glossdef>

<para>

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

that replays WAL during crash recovery and in a

<glossterm linkend="glossary-replication">physical replica</glossterm>.

</para>

<para>

(The name is historical: the startup process was named before

replication was implemented; the name refers to its task as it

relates to the server startup following a crash.)

</para>

</glossdef>

</glossentry>

<glossentry id="glossary-sql-object">

<glossterm>SQL object</glossterm>

<glossdef>

<glossterm>Stats collector (process)</glossterm>

<glossdef>

<para>

This process collects statistical information about the

<glossterm linkend="glossary-instance">instance</glossterm>'s activities.

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

which, if enabled, receives statistical information

about the <glossterm linkend="glossary-instance">instance</glossterm>'s

activities.

</para>

<para>

For more information, see

<glossterm>WAL archiver (process)</glossterm>

<glossdef>

<para>

A process that saves copies of <glossterm linkend="glossary-wal-file">WAL files</glossterm>

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

which, if enabled, 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>

</glossdef>

</glossentry>

<glossentry id="glossary-wal-receiver">

<glossterm>WAL receiver</glossterm>

<glossdef>

<para>

An <glossterm linkend="glossary-auxiliary-proc">auxiliary process</glossterm>

that runs on a <glossterm linkend="glossary-replica">replica</glossterm>

to receive WAL from the

<glossterm linkend="glossary-primary-server">primary server</glossterm>

for replay by the

<glossterm linkend="glossary-startup-process">startup process</glossterm>.

</para>

<para>

For more information, see

<xref linkend="warm-standby"/>.

</para>

</glossdef>

</glossentry>

<glossentry>

<glossterm>WAL segment</glossterm>

<glosssee otherterm="glossary-wal-file" />

</glossentry>

<glossentry id="glossary-wal-sender">

<glossterm>WAL sender (process)</glossterm>

<glossdef>

<para>

A special <glossterm linkend="glossary-backend">backend process</glossterm>

that streams WAL over a network. The receiving end can be a

<glossterm linkend="glossary-wal-receiver">WAL receiver</glossterm>

in a <glossterm linkend="glossary-replica">replica</glossterm>,

<xref linkend="app-pgreceivewal"/>, or any other client program

that speaks the replication protocol.

</para>

</glossdef>

</glossentry>

<glossentry id="glossary-wal-writer">

<glossterm>WAL writer (process)</glossterm>

<glossdef>