</listitem>

<listitem>

<para>

To control the workload in your system, set themaximal number

To control the workload in your system, set themaximum number

of background workers that can run simultaneously on each

database:

</para>

The <filename>pgpro_scheduler</filename> extension starts a

separate background worker for the system, each database, and

each monitored job. For example, if you work with two databases

and set themaximal number of workers to 5,

and set themaximum number of workers to 5,

<filename>pgpro_scheduler</filename> can use up to 13 workers at

peak times: one worker is supervising the system, two workers

are monitoring the two databases, and 10 workers can be started

<para>

Alternatively, you can modify <filename>pgpro_scheduler</filename>

settings in the <filename>postgresql.conf</filename> file. In this

case, all databases will have the samemaximal number of

case, all databases will have the samemaximum number of

background workers:

</para>

<programlisting>

If all background workers are busy at the specified time, the

job waits for the next available worker. By default, the

<filename>pgpro_scheduler</filename> can wait forever. You can

limit themaximal wait time by setting the

limit themaximum wait time by setting the

<literal>last_start_available</literal> key, in the <link linkend="datatype-datetime">time interval</link> format.

If the timeout is reached, <filename>pgpro_scheduler</filename>

cancels the job execution.

</para>

</listitem>

<listitem>

<para>Define themaximal wait time before the function gets

<para>Define themaximum wait time before the function gets

executed using the <literal>last_start_available</literal>

key. If the timeout is reached, <filename>pgpro_scheduler</filename> cancels the job.

</para>

<sect2 id="pgpro-scheduler-reference">

<title>Reference</title>

<sect3 id="pgpro-scheduler-guc-variables">

<title>Variables</title>

<title>GUCVariables</title>

<variablelist>

<varlistentry id="pgpro-scheduler-schedule-enable" xreflabel="schedule.enable">

<term><varname>schedule.enable</varname> (<type>boolean</type>)

</term>

<listitem>

<para>

Specifies themaximal number of simultaneously running jobs in one database.</para>

Specifies themaximum number of simultaneously running jobs in one database.</para>

<para>Default: <literal>2</literal>.

</para>

</listitem>

use_same_transaction boolean, -- true if an array of SQL

-- commands will be executed

-- in a single transaction

last_start_available interval, --maximal wait time for

last_start_available interval, --maximum wait time for

-- the scheduled job if all

-- allowed workers are busy

max_instances int, --maximal number of simultaneously

max_instances int, --maximum number of simultaneously

-- running job instances

max_run_time interval, --maximal execution time

max_run_time interval, --maximum execution time

onrollback text, -- SQL statement to execute

-- if the main transaction fails

-- commands will be executed

-- in a single transaction

started timestamp, -- timestamp of the job execution start

last_start_available timestamp, --maximal wait time for

last_start_available timestamp, --maximum wait time for

-- the scheduled job if all

-- allowed workers are busy

finished timestamp, -- timestamp of the job

-- execution finish

max_run_time interval, --maximal execution time

max_run_time interval, --maximum execution time

max_instances int, -- the number of simultaneously

-- running job instances

onrollback text, -- SQL statement to execute if the main

<type>interval</type>

</entry>

<entry>

Optional. Themaximal time interval to postpone the job

execution if themaximal number of allowed workers

Optional. Themaximum time interval to postpone the job

execution if themaximum number of allowed workers

reached at the scheduled moment. For example, if this

key is set to '00:02:34', the job will wait for 2

minutes 34 seconds. If this key is NULL or not set, the

<type>interval</type>

</entry>

<entry>

Optional. Themaximal time interval during which the

Optional. Themaximum time interval during which the

scheduled job can be executed. If this key is NULL or

not set, there are no time limits. Default: NULL.

</entry>

Return values:

<itemizedlist>

<listitem><para><literal>true</literal> &mdash; the job was activated successfully.</para></listitem>

<listitem><para><literal>false</literal> &mdash; jobactivaction failed.</para></listitem>

<listitem><para><literal>false</literal> &mdash; jobactivation failed.</para></listitem>

</itemizedlist>

</para>

</listitem>