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|
<!-- doc/src/sgml/runtime.sgml -->
<chapter id="runtime">
<title>Server Setup and Operation</title>
<para>
This chapter discusses how to set up and run the <productname>Pgpool-II</> server
and its interactions with the operating system.
</para>
<sect1 id="kernel-resource">
<title>Managing kernel resouces</title>
<indexterm>
<primary>kernel resouces</primary>
</indexterm>
<para>
To run <productname>Pgpool-II</productname> System V shared memory
and System V semaphore are necessary. Although on linux enough
amount of both resources are provided, other platforms may need to
configure the kernel parameters.
</para>
<para>
The minimum requirement of System V shared memory is around 140 MB.
If you plan to use more than default 64MB
of <link linkend="runtime-in-memory-query-cache">query
cache</link>, you may need more shared memory. Number of necessary
shared memory segments is 3. Usually the kernel provides enough
shared memory segments.
</para>
<para>
The minimum requirement of System V semaphore is around 10. Number
of necessary semaphore sets is 3. Usually the kernel provides
enough semaphore sets.
</para>
</sect1>
<sect1 id="pgpool-II-user">
<title>The <productname>Pgpool-II</productname> User Account</title>
<indexterm>
<primary>Pgpool-II user</primary>
</indexterm>
<para>
As with any server daemon that is accessible to the outside world,
it is advisable to run <productname>Pgpool-II</productname> under a
separate user account. This user account should only own the data
that is managed by the server, and should not be shared with other
daemons. (For example, using the user <literal>nobody</literal> is a bad
idea.) It is not advisable to install executables owned by this
user because compromised systems could then modify their own
binaries.
</para>
<para>
To add a Unix user account to your system, look for a command
<command>useradd</command> or <command>adduser</command>. The user
name <systemitem>pgpool</systemitem> is often used, and is assumed
throughout this book, but you can use another name if you like.
</para>
</sect1>
<sect1 id="configuring-pcp-conf">
<title>Configuring pcp.conf</title>
<indexterm>
<primary>pcp configuration</primary>
</indexterm>
<para>
<productname>Pgpool-II</productname> provides a interface
for administrators to perform management operation, such as
getting <productname>Pgpool-II</productname> status or terminating
<productname>Pgpool-II</productname> processes
remotely. <filename>pcp.conf</filename> is the user/password file
used for authentication by this interface. All operation modes
require the <filename>pcp.conf</filename> file to be set. A
<filename>$prefix/etc/pcp.conf.sample</filename> file is created
during the installation
of <productname>Pgpool-II</productname>. Copy the file as
<filename>$prefix/etc/pcp.conf</filename> and add your user name and password
to it.
<screen>
<prompt>$</> <userinput>cp $prefix/etc/pcp.conf.sample $prefix/etc/pcp.conf</userinput>
</screen>
An empty line or a line starting with <literal>#</literal> is treated as a
comment and will be ignored. A user name and its associated
password must be written as one line using the following format:
<synopsis>
<replaceable>username</>:<replaceable>[md5 encrypted password]</>
</synopsis>
<replaceable>[md5 encrypted password]</> can be produced with the <filename>$prefix/bin/pg_md5</> command.
<screen>
<prompt>$</> <userinput>pg_md5 your_password</userinput>
1060b7b46a3bd36b3a0d66e0127d0517
</screen>
If you don't want pass the password as the argument, execute <command>pg_md5 -p</command>.
<screen>
<prompt>$</> <userinput>pg_md5 -p</userinput>
password: <userinput>your_password</userinput>
</screen>
The <filename>pcp.conf</filename> file must be readable by the
user who executes <productname>Pgpool-II</productname>.
</para>
</sect1>
<sect1 id="configuring-pgpool">
<title>Configuring Pgpool-II</title>
<indexterm>
<primary>Pgpool-II configuration</primary>
</indexterm>
<sect2 id="configuring-pgpool-conf">
<title>Configuring pgpool.conf</title>
<para>
<filename>pgpool.conf</filename> is the main configuration file
of <productname>Pgpool-II</productname>. You need to specify the
path to the file when
starting <productname>Pgpool-II</productname>
using <option>-f</option> option.
<filename>pgpool.conf</filename> is located
at <filename>$prefix/etc/pgpool.conf</filename> by default,
if it installed from source code.
</para>
<para>
To specify the <productname>Pgpool-II</productname> clustering
mode, set <xref linkend="guc-backend-clustering-mode"> parameter
to the value explained below.
</para>
<table id="backend-clustering-mode-table">
<title><xref linkend="guc-backend-clustering-mode"> value in pgpool.conf</title>
<tgroup cols="2">
<thead>
<row>
<entry>Clustering mode</entry>
<entry>value</entry>
</row>
</thead>
<tbody>
<row>
<entry>Streaming replication mode</entry>
<entry><literal>streaming_replication</literal></entry>
</row>
<row>
<entry>Replication mode</entry>
<entry><literal>native_replication</literal></entry>
</row>
<row>
<entry>Logical replication mode</entry>
<entry><literal>logical_replication</literal> </entry>
</row>
<row>
<entry>Slony mode</entry>
<entry><literal>slony</literal></entry>
</row>
<row>
<entry>Snapshot isolation mode</entry>
<entry><literal>snapshot_isolation</literal></entry>
</row>
<row>
<entry>Raw mode</entry>
<entry><literal>raw</literal> </entry>
</row>
</tbody>
</tgroup>
</table>
<para>
These configuration files are located at /usr/local/etc with
default installation from source code.
You can copy one of them as <filename>pgpool.conf</filename>.
(probably you need root privilege for this)
<programlisting>
# cd /usr/local/etc
# cp pgpool.conf.sample pgpool.conf
</programlisting>
</para>
</sect2>
<sect2 id="running-mode">
<title>Clustering mode of Pgpool-II</title>
<indexterm zone="running-mode">
<primary>streaming replication mode</primary>
</indexterm>
<indexterm zone="running-mode">
<primary>native replication mode</primary>
</indexterm>
<indexterm zone="running-mode">
<primary>main replica mode</primary>
</indexterm>
<indexterm zone="running-mode">
<primary>logical replication mode</primary>
</indexterm>
<indexterm zone="running-mode">
<primary>snapshot isolation mode</primary>
</indexterm>
<para>
There are six different <link linkend="guc-backend-clustering-mode">clustering modes</link> in
<productname>Pgpool-II</>: streaming replication mode, logical
replication mode, main replica mode (slony mode), native
replication mode, raw mode and snapshot isolation mode. In any
mode, <productname>Pgpool-II</> provides connection pooling, and
automatic fail over. Online recovery can be used only with
streaming replication mode, snapshot isolation mode and native
replication mode. See <xref linkend="runtime-online-recovery">
for more details of online recovery.
</para>
<para>
Those modes are exclusive each other and cannot be changed after
starting the server. You should make a decision which to use in
the early stage of designing the system. If you are not sure, it
is recommended to use the streaming replication mode or the
snapshot isolation mode.
</para>
<para>
The <firstterm>streaming replication mode</firstterm> can be used
with <productname>PostgreSQL</> servers operating streaming
replication. In this mode, <productname>PostgreSQL</> is
responsible for synchronizing databases. This mode is widely used
and most recommended way to use <productname>Pgpool-II</>. Load
balancing is possible in the mode. visibility consistency among
nodes is not guaranteed.
</para>
<para>
In the <firstterm>snapshot isolation mode</firstterm>
<productname>Pgpool-II</> is responsible for synchronizing
databases. The advantage for the mode is the synchronization is
done in synchronous way: writing to the database does not return
until all of <productname>PostgreSQL</> servers finish the write
operation. Also it guarantees the visibility consistency among
nodes. To put it simply, it means that the visibility rule of
transactions on single server is applied to a cluster consisting
of multiple servers as well. This is a remarkable feature of the
snapshot isolation mode in
<productname>Pgpool-II</productname>. In fact, the snapshot
isolation mode in <productname>Pgpool-II</productname> is the only
system which guarantees the visibility consistency among nodes
without modifications to <productname>PostgreSQL</> at the moment.
Because of this, applications do not need to recognize that they
are using a cluster consisting of
<productname>PostgreSQL</productname> servers, rather than a
single <productname>PostgreSQL</productname> system. However in
this mode the transaction isolation level <emphasis>must be
REPEATABLE READ</emphasis>. You need to set
<filename>postgresql.conf</filename> like this:
<programlisting>
default_transaction_isolation = 'repeatable read'
</programlisting>
</para>
<para>
Also you need to aware that performance in the mode may be worse
than the streaming replication mode and native replication mode
due to the overhead to keep the consistency in transactions.
</para>
<para>
In the <firstterm>native replication mode</firstterm>,
<productname>Pgpool-II</> is responsible for synchronizing
databases. The advantage for the mode is the synchronization is
done in synchronous way: writing to the database does not return
until all of <productname>PostgreSQL</> servers finish the write
operation. As visibility consistency among nodes is not
guaranteed, it is recommended to use the snapshot isolation mode
except you want to use other than REPEATABLE READ isolation mode.
Load balancing is possible in the mode.
</para>
<para>
The <firstterm>logical replication mode</firstterm> can be used
with <productname>PostgreSQL</> servers operating logical
replication. In this mode, <productname>PostgreSQL</> is
responsible for synchronizing tables. Load balancing is possible
in the mode. Since logical replication does not replicate all
tables, it's user's responsibility to replicate the table which
could be load balanced. <productname>Pgpool-II</> load balances
all tables. This means that if a table is not
replicated, <productname>Pgpool-II</> may lookup outdated tables
in the subscriber side.
</para>
<para>
The <firstterm>main replica mode</firstterm> (slony mode)
can be used with <productname>PostgreSQL</> servers
operating <productname>Slony</>. In this
mode, <productname>Slony</>/<productname>PostgreSQL</> is
responsible for synchronizing
databases. Since <productname>Slony-I</> is being obsoleted by
streaming replication, we do not recommend to use this mode
unless you have specific reason to
use <productname>Slony</>. Load balancing is possible in the
mode.
</para>
<para>
In the <firstterm>raw
mode</firstterm>, <productname>Pgpool-II</> does not care about
the database synchronization. It's user's responsibility to make
the whole system does a meaningful thing. Load balancing
is <emphasis>not</emphasis> possible in the mode.
</para>
</sect2>
<sect2 id="process-management-mode">
<title>Process management modes</title>
<indexterm zone="running-mode">
<primary>dynamic process management</primary>
</indexterm>
<indexterm zone="running-mode">
<primary>static process management</primary>
</indexterm>
<para>
<productname>Pgpool-II</> implements a multi-process architecture where
each child process can handle exactly one client connection at any time.
The total number of concurrent client connections <productname>Pgpool-II</>
can handle is configured by the
<link linkend="guc-num-init-children">num_init_children</link> config parameter.
<productname>Pgpool-II</> supports two child process management modes.
<firstterm>Dynamic</firstterm> and <firstterm>Static</firstterm>.
In static process management mode, <productname>Pgpool-II</> pre-forks the
num_init_children number of child
process at startup, and each child process keeps listening for incoming
client connection. While with dynamic process management mode,
<productname>Pgpool-II</> keeps track of idle processes and forks or kills
processes to keep this number within the specified boundaries.
</para>
<para>
<xref linkend="guc-process-management-mode"> is not available prior to
<productname>Pgpool-II </productname><emphasis>V4.4</emphasis>.
</para>
</sect2>
</sect1>
<sect1 id="configuring-backend-info">
<title>Configuring backend information</title>
<para>
For <productname>Pgpool-II</productname> to recognize <productname>PostgreSQL</>
backend servers, you need to configure <varname>backend*</varname>
in <filename>pgpool.conf</filename>. For starters, at
least <xref linkend="guc-backend-hostname">
and <xref linkend="guc-backend-port"> parameters are required to
be set up to start <productname>Pgpool-II</> server.
</para>
<sect2 id="backend-settings">
<title>Backend Settings</title>
<para>
Backend <productname>PostgreSQL</> used by <productname>Pgpool-II</> must be specified in <filename>pgpool.conf</filename>.
See <xref linkend="runtime-config-backend-settings">
</para>
<!--
<variablelist>
<varlistentry id="guc-backend-hostname" xreflabel="backend_hostname">
<term><varname>backend_hostname</varname> (<type>string</type>)
<indexterm>
<primary><varname>backend_hostname</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
<varname>backend_hostname</varname> specifies where to
connect to the <productname>PostgreSQL</productname>
backend. It is used
by <productname>Pgpool-II</productname> to communicate
with the server.
</para>
<para>
For TCP/IP communication, this parameter can take a hostname
or an IP address. If this begins with a slash, it specifies
Unix-domain communication rather than TCP/IP; the value is
the name of the directory in which the socket file is
stored. The default behavior when backend_hostname is empty
('') is to connect to a Unix-domain socket in /tmp.
</para>
<para>
Multiple backends can be specified by adding a number at the
end of the parameter name (e.g.backend_hostname0). This
number is referred to as "DB node ID", and it starts from
0. The backend which was given the DB node ID of 0 will be
called "Main DB". When multiple backends are defined, the
service can be continued even if the Main DB is down (not
true in some modes). In this case, the youngest DB node ID
alive will be the new Main DB.
</para>
<para>
Please note that the DB node which has id 0 has no special
meaning if operated in streaming replication mode. Rather,
you should care about if the DB node is the "primary node" or
not. See Streaming Replication for more details.
</para>
<para>
If you plan to use only one PostgreSQL server, specify it by
backend_hostname0.
</para>
<para>
New nodes can be added in this parameter by reloading a
configuration file. However, values cannot be updated so
you must restart <productname>Pgpool-II</productname> in
that case.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-backend-port" xreflabel="backend_port">
<term><varname>backend_port</varname> (<type>integer</type>)
<indexterm>
<primary><varname>backend_port</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
<varname>backend_port</varname> specifies the port number
of the backends. Multiple backends can be specified by
adding a number at the end of the parameter name
(e.g. backend_port0). If you plan to use only one
PostgreSQL server, specify it by backend_port0.
</para>
<para>
New backend ports can be added in this parameter by
reloading a configuration file. However, values cannot be
updated so you must
restart <productname>Pgpool-II</productname> in that case.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-backend-data-directory" xreflabel="backend_data_directory">
<term><varname>backend_data_directory</varname> (<type>string</type>)
<indexterm>
<primary><varname>backend_data_directory</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
<varname>backend_data_directory</varname> specifies the
database directory. Multiple backends can be
specified by adding a number at the end of the parameter
name (e.g. backend_data_directory0). If you plan to use
only one PostgreSQL server, specify it by
backend_data_directory0.
</para>
<para>
New backend data_directories can be added in this parameter
by reloading a configuration file. However, values cannot
be updated so you must
restart <productname>Pgpool-II</productname> in that case.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-backend-flag" xreflabel="backend_flag">
<term><varname>backend_flag</varname> (<type>string</type>)
<indexterm>
<primary><varname>backend_flag</varname> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
<varname>backend_flag</varname> controls various backend
behavior. Multiple backends can be specified by adding a
number at the end of the parameter name
(e.g. backend_flag0). If you plan to use only one
PostgreSQL server, specify it by backend_flag0.
</para>
<para>
New backend flags can be added in this parameter by
reloading a configuration file. Currently followings are
allowed. Multiple flags can be specified by using "|".
</para>
<table id="backend-flag-table">
<title>Backend flags</title>
<tgroup cols="2">
<thead>
<row>
<entry>Flag</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><literal>ALLOW_TO_FAILOVER</literal></entry>
<entry>Allow to failover or detaching backend. This
is the default. You cannot specify with
DISALLOW_TO_FAILOVER at a same time.</entry>
</row>
<row>
<entry><literal>DISALLOW_TO_FAILOVER</literal></entry>
<entry>This is useful when you protect backend by
using HA (High Availability) softwares such as
Heartbeat or Pacemaker. You cannot specify with
ALLOW_TO_FAILOVER at a same time.
</entry>
</row>
</tbody>
</tgroup>
</table>
</listitem>
</varlistentry>
</variablelist>
-->
</sect2>
</sect1>
<sect1 id="server-start">
<title>Starting Pgpool-II and PostgreSQL</title>
<para>
To start <productname>Pgpool-II</productname>, execute:
<screen>
$ <userinput>pgpool -f /usr/local/etc/pgpool.conf -F /usr/local/etc/pcp.conf</userinput>
</screen>
which will start the server running in the background. "-f"
specifies the path to the main pgpool configuration file and "-F"
specifies the path to the configuration file of pcp server, which
is the control server for <productname>Pgpool-II</productname>. For
other options of the command please take a look at <xref
linkend="pgpool"> manual.
</para>
<para>
Before starting <productname>Pgpool-II</productname>, you must
start <productname>PostgreSQL</productname> because if
<productname>PostgreSQL</productname> has not started yet,
<productname>Pgpool-II</productname> triggers failover process and
makes <productname>PostgreSQL</productname> is in down status.
</para>
<para>
If you have difficulty in controlling the startup sequence of
<productname>PostgreSQL</productname>, for example
<productname>Pgpool-II</productname> and
<productname>PostgreSQL</productname> are installed on different
servers, you can make <xref
linkend="guc-search-primary-node-timeout"> longer (the default is 5
minutes) so that <productname>Pgpool-II</productname> waits for
<productname>PostgreSQL</productname> starts up until <xref
linkend="guc-search-primary-node-timeout"> expires. If
<productname>PostgreSQL</productname> starts up before <xref
linkend="guc-search-primary-node-timeout"> expires,
<productname>Pgpool-II</productname> should start up without
problem. If <xref linkend="guc-search-primary-node-timeout">
expires before <productname>PostgreSQL</productname> starts up, no
primary node will be detected, which means you cannot execute
DML/DDL. You need to restart <productname>Pgpool-II</productname>
in this case. To confirm that the primary node exists you can use
<xref linkend="sql-show-pool-nodes"> command.
</para>
<para>
Please note <xref linkend="guc-search-primary-node-timeout"> can
only be used in the streaming replication mode because the
parameter is only valid in the mode. See <xref
linkend="running-mode"> for more details about streaming
replication mode. For other mode, tweak the health check (see <xref
linkend="runtime-config-health-check">) parameters so that there's
enough time before <productname>PostgreSQL</productname> becomes
available.
</para>
<para>
If health check detects that <productname>PostgreSQL</productname>
is not available before <productname>Pgpool-II</productname> starts
up, some or all <productname>PostgreSQL</productname> are
recognized in "down" status. In this case you need to manually put
the <productname>PostgreSQL</productname> server in "up" state by
using <xref linkend="pcp-attach-node"> command. If a client tries
to connect to <productname>Pgpool-II</productname> before
<productname>PostgreSQL</productname> is available, failover could
be triggered. In this case you also need to execute <xref
linkend="pcp-attach-node"> command to put the
<productname>PostgreSQL</productname> server in "up" state.
</para>
</sect1>
<sect1 id="server-stop">
<title>Stopping Pgpool-II and PostgreSQL</title>
<indexterm zone="server-stop">
<primary>shutdown</primary>
</indexterm>
<para>
To stop <productname>Pgpool-II</productname>, execute:
<screen>
$ <userinput>pgpool -f /usr/local/etc/pgpool.conf -F /usr/local/etc/pcp.conf -m fast stop</userinput>
</screen>
"-m" option specifies how gently stops
<productname>Pgpool-II</productname>. "fast" means shutdown
<productname>Pgpool-II</productname> immediately even if there are
existing connections from clients. You can specify "smart" to the
option, which force <productname>Pgpool-II</productname> to wait
until all clients are disconnected from
<productname>Pgpool-II</productname>. But this could make
<productname>Pgpool-II</productname> wait forever and this may
result in sending SIGKILL signal from the operating system and
leaving garbage, which will bring troubles next time when you start
<productname>Pgpool-II</productname>.
</para>
<para>
After shutting down <productname>Pgpool-II</productname>, you can
shutdown <productname>PostgreSQL</productname>.
</para>
</sect1>
<sect1 id="server-temporarily-shutdown">
<title>Temporarily Shutting Down PostgreSQL</title>
<indexterm zone="server-temporarily-shutdown">
<primary>shutdown</primary>
</indexterm>
<para>
Sometimes you want to temporarily stop or restart
<productname>PostgreSQL</productname> to maintain or version up
it. In this section how to perform the task with minimum downtime.
</para>
<sect2 id="using-pcp-detach-node">
<title>Using pcp_detach_node command</title>
<para>
If you stop <productname>PostgreSQL</productname> by using
<command>pg_ctl</command>, failover will not happen until
<productname>Pgpool-II</productname> detects it by the health
check depending on the health check settings and it will take
sometime to detach <productname>PostgreSQL</productname>.
Especially if <link linkend="tutorial-watchdog">Watchdog</link> is
enabled and <xref linkend="guc-failover-require-consensus"> is on,
<productname>Pgpool-II</productname> will not start failover until
more than half of watchdog nodes agree that
<productname>PostgreSQL</productname> is stopped. If you detach
the node by using <xref linkend="pcp-detach-node">, failover will
immediately start regardless the settings of health check. Please
note that the detached <productname>PostgreSQL</productname> node
is not actually stopped and if necessary, you need to manually
stop it.
</para>
</sect2>
<sect2 id="using-backend-flag">
<title>Using backend_flag</title>
<para>
Stopping or restarting <productname>PostgreSQL</productname>
causes failover. If the running mode is not streaming replication
mode, or the server is a standby server in streaming replication
mode, probably that's not a big deal because clients can always
use other servers in the cluster. However if the server is primary
server, it will cause change of primary server by promoting one of
the standby servers. Moreover if there's only one server remains
in the cluster, there are no alternative server or standby server
which can be promoted.
</para>
<para>
In this case you can use <xref linkend="guc-backend-flag"> to avoid
failover. By setting below in pgpool.conf will avoid failover of
backend0.
<programlisting>
backend_flag0 = DISALLOW_TO_FAILOVER
</programlisting>
This will take effect by reloading or restarting
<productname>Pgpool-II</productname>. If this flag is set, failover
will not happen if the backend is not available. While the backend
is not available, clients will get error message:
<programlisting>
psql: error: could not connect to server: FATAL: failed to create a backend connection
DETAIL: executing failover on backend
</programlisting>
After restarting the backend, clients can connect as usual.
To allow failover on the backend again, you can set:
<programlisting>
backend_flag0 = ALLOW_TO_FAILOVER
</programlisting>
and reload or restart <productname>Pgpool-II</productname>.
</para>
</sect2>
</sect1>
<sect1 id="backup">
<title>Backing up PostgreSQL database</title>
<indexterm zone="backup">
<primary>backup</primary>
</indexterm>
<para>
If you plan to backup <productname>PostgreSQL</productname>
database
using <command>pg_dump</command>, <command>pg_basebackup</command>
or any other tools, we strongly recommend to run the commands
against <productname>PostgreSQL</productname>
directly. As <productname>Pgpool-II</productname> is a proxy
software, it gives an overhead for relaying message packets. Since
obtaining a backup tends to produce lots of packets, performing
backup through <productname>Pgpool-II</productname> will be slow
compared with directly
connecting <productname>PostgreSQL</productname> unless the
database is very small.
</para>
<para>
Moreover, parallel <command>pg_dump</command> raises error if it is
executed through <productname>Pgpool-II</productname> because the
command handles snapshot id, which is a database depending object.
</para>
<para>
In most cases you want to choose primary server as the backup
target. If you want backup standby server, you have to be very
careful in choosing the right <productname>PostgreSQL</productname>
server to obtain a backup because if the data is outdated, you are
likely to have outdated database backup. You can
use <xref linkend="SQL-SHOW-POOL-NODES">
or <xref linkend="PCP-NODE-INFO"> to know how the standby server
catches up the primary server.
</para>
</sect1>
</chapter>
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