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Add session_preload_libraries configuration parameter

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This is like shared_preload_libraries except that it takes effect at
backend start and can be changed without a full postmaster restart.  It
is like local_preload_libraries except that it is still only settable by
a superuser.  This can be a better way to load modules such as
auto_explain.

Since there are now three preload parameters, regroup the documentation
a bit.  Put all parameters into one section, explain common
functionality only once, update the descriptions to reflect current and
future realities.

Reviewed-by: Dimitri Fontaine <dimitri@2ndQuadrant.fr>
This commit is contained in:
Peter Eisentraut 2013-06-12 22:28:24 -04:00
parent f3ab5d4696
commit 070518ddab
7 changed files with 193 additions and 124 deletions
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5
doc/src/sgml/auto-explain.sgml
View File

@ -24,7 +24,8 @@ LOAD 'auto_explain';
</programlisting>
(You must be superuser to do that.) More typical usage is to preload
it into all sessions by including <literal>auto_explain</> in
it into some or all sessions by including <literal>auto_explain</> in
<xref linkend="guc-session-preload-libraries"> or
<xref linkend="guc-shared-preload-libraries"> in
<filename>postgresql.conf</>. Then you can track unexpectedly slow queries
no matter when they happen. Of course there is a price in overhead for
@ -185,7 +186,7 @@ LOAD 'auto_explain';
<programlisting>
# postgresql.conf
shared_preload_libraries = 'auto_explain'
session_preload_libraries = 'auto_explain'
auto_explain.log_min_duration = '3s'
</programlisting>

281
doc/src/sgml/config.sgml
View File

@ -1252,66 +1252,6 @@ include 'filename'
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-shared-preload-libraries" xreflabel="shared_preload_libraries">
<term><varname>shared_preload_libraries</varname> (<type>string</type>)</term>
<indexterm>
<primary><varname>shared_preload_libraries</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
This variable specifies one or more shared libraries
to be preloaded at server start. For example,
<literal>'$libdir/mylib'</literal> would cause
<literal>mylib.so</> (or on some platforms,
<literal>mylib.sl</>) to be preloaded from the installation's
standard library directory.
All library names are converted to lower case unless double-quoted.
If more than one library is to be loaded, separate their names
with commas. This parameter can only be set at server start.
</para>
<para>
<productname>PostgreSQL</productname> procedural language
libraries can be preloaded in this way, typically by using the
syntax <literal>'$libdir/plXXX'</literal> where
<literal>XXX</literal> is <literal>pgsql</>, <literal>perl</>,
<literal>tcl</>, or <literal>python</>.
</para>
<para>
By preloading a shared library, the library startup time is avoided
when the library is first used. However, the time to start each new
server process might increase slightly, even if that process never
uses the library. So this parameter is recommended only for
libraries that will be used in most sessions.
</para>
<note>
<para>
On Windows hosts, preloading a library at server start will not reduce
the time required to start each new server process; each server process
will re-load all preload libraries. However, <varname>shared_preload_libraries
</varname> is still useful on Windows hosts because some shared libraries may
need to perform certain operations that only take place at postmaster start
(for example, a shared library may need to reserve lightweight locks
or shared memory and you can't do that after the postmaster has started).
</para>
</note>
<para>
If a specified library is not found,
the server will fail to start.
</para>
<para>
Every PostgreSQL-supported library has a <quote>magic
block</> that is checked to guarantee compatibility.
For this reason, non-PostgreSQL libraries cannot be
loaded in this way.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
@ -5514,6 +5454,171 @@ SET XML OPTION { DOCUMENT | CONTENT };
</variablelist>
</sect2>
<sect2 id="runtime-config-client-preload">
<title>Shared Library Preloading</title>
<para>
Several settings are available for preloading shared libraries into the
server, in order to load additional functionality or achieve performance
benefits. For example, a setting of
<literal>'$libdir/mylib'</literal> would cause
<literal>mylib.so</> (or on some platforms,
<literal>mylib.sl</>) to be preloaded from the installation's standard
library directory. The differences between the settings are when they
take effect and what privileges are required to change them.
</para>
<para>
<productname>PostgreSQL</productname> procedural language libraries can
be preloaded in this way, typically by using the
syntax <literal>'$libdir/plXXX'</literal> where
<literal>XXX</literal> is <literal>pgsql</>, <literal>perl</>,
<literal>tcl</>, or <literal>python</>.
</para>
<para>
For each parameter, if more than one library is to be loaded, separate
their names with commas. All library names are converted to lower case
unless double-quoted.
</para>
<para>
Only shared libraries specifically intended to be used with PostgreSQL
can be loaded this way. Every PostgreSQL-supported library has
a <quote>magic block</> that is checked to guarantee compatibility. For
this reason, non-PostgreSQL libraries cannot be loaded in this way. You
might be able to use operating-system facilities such
as <envar>LD_PRELOAD</envar> for that.
</para>
<para>
In general, refer to the documentation of a specific module for the
recommended way to load that module.
</para>
<variablelist>
<varlistentry id="guc-local-preload-libraries" xreflabel="local_preload_libraries">
<term><varname>local_preload_libraries</varname> (<type>string</type>)</term>
<indexterm>
<primary><varname>local_preload_libraries</> configuration parameter</primary>
</indexterm>
<indexterm>
<primary><filename>$libdir/plugins</></primary>
</indexterm>
<listitem>
<para>
This variable specifies one or more shared libraries that are to be
preloaded at connection start. This parameter cannot be changed after
the start of a particular session. If a specified library is not
found, the connection attempt will fail.
</para>
<para>
This option can be set by any user. Because of that, the libraries
that can be loaded are restricted to those appearing in the
<filename>plugins</> subdirectory of the installation's
standard library directory. (It is the database administrator's
responsibility to ensure that only <quote>safe</> libraries
are installed there.) Entries in <varname>local_preload_libraries</>
can specify this directory explicitly, for example
<literal>$libdir/plugins/mylib</literal>, or just specify
the library name &mdash; <literal>mylib</literal> would have
the same effect as <literal>$libdir/plugins/mylib</literal>.
</para>
<para>
Unless a module is specifically designed to be used in this way by
non-superusers, this is usually not the right setting to use. Look
at <xref linkend="guc-session-preload-libraries"> instead.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-session-preload-libraries" xreflabel="session_preload_libraries">
<term><varname>session_preload_libraries</varname> (<type>string</type>)</term>
<indexterm>
<primary><varname>session_preload_libraries</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
This variable specifies one or more shared libraries that are to be
preloaded at connection start. Only superusers can change this setting.
The parameter value only takes effect at the start of the connection.
Subsequent changes have no effect. If a specified library is not
found, the connection attempt will fail.
</para>
<para>
The intent of this feature is to allow debugging or
performance-measurement libraries to be loaded into specific sessions
without an explicit
<command>LOAD</> command being given. For
example, <xref linkend="auto-explain"> could be enabled for all
sessions under a given user name by setting this parameter
with <command>ALTER ROLE SET</>. Also, this parameter can be changed
without restarting the server (but changes only take effect when a new
session is started), so it is easier to add new modules this way, even
if they should apply to all sessions.
</para>
<para>
Unlike <xref linkend="guc-shared-preload-libraries">, there is no large
performance advantage to loading a library at session start rather than
when it is first used. There is some advantage, however, when
connection pooling is used.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-shared-preload-libraries" xreflabel="shared_preload_libraries">
<term><varname>shared_preload_libraries</varname> (<type>string</type>)</term>
<indexterm>
<primary><varname>shared_preload_libraries</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
This variable specifies one or more shared libraries to be preloaded at
server start. with commas. This parameter can only be set at server
start. If a specified library is not found, the server will fail to
start.
</para>
<para>
Some libraries need to perform certain operations that can only take
place at postmaster start, such as allocating shared memory, reserving
light-weight locks, or starting background workers. Those libraries
must be loaded at server start through this parameter. See the
documentation of each library for details.
</para>
<para>
Other libraries can also be preloaded. By preloading a shared library,
the library startup time is avoided when the library is first used.
However, the time to start each new server process might increase
slightly, even if that process never uses the library. So this
parameter is recommended only for libraries that will be used in most
sessions. Also, changing this parameter requires a server restart, so
this is not the right setting to use for short-term debugging tasks,
say. Use <xref linkend="guc-session-preload-libraries"> for that
instead.
</para>
<note>
<para>
On Windows hosts, preloading a library at server start will not reduce
the time required to start each new server process; each server process
will re-load all preload libraries. However, <varname>shared_preload_libraries
</varname> is still useful on Windows hosts for libraries that need to
perform operations at postmaster start time..
</para>
</note>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="runtime-config-client-other">
<title>Other Defaults</title>
@ -5585,62 +5690,6 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
</listitem>
</varlistentry>
<varlistentry id="guc-local-preload-libraries" xreflabel="local_preload_libraries">
<term><varname>local_preload_libraries</varname> (<type>string</type>)</term>
<indexterm>
<primary><varname>local_preload_libraries</> configuration parameter</primary>
</indexterm>
<indexterm>
<primary><filename>$libdir/plugins</></primary>
</indexterm>
<listitem>
<para>
This variable specifies one or more shared libraries that are
to be preloaded at connection start. If more than one library
is to be loaded, separate their names with commas. All library
names are converted to lower case unless double-quoted.
This parameter cannot be changed after the start of a particular
session.
</para>
<para>
Because this is not a superuser-only option, the libraries
that can be loaded are restricted to those appearing in the
<filename>plugins</> subdirectory of the installation's
standard library directory. (It is the database administrator's
responsibility to ensure that only <quote>safe</> libraries
are installed there.) Entries in <varname>local_preload_libraries</>
can specify this directory explicitly, for example
<literal>$libdir/plugins/mylib</literal>, or just specify
the library name &mdash; <literal>mylib</literal> would have
the same effect as <literal>$libdir/plugins/mylib</literal>.
</para>
<para>
Unlike <xref linkend="guc-shared-preload-libraries">, there is no
performance advantage to loading a library at session
start rather than when it is first used. Rather, the intent of
this feature is to allow debugging or performance-measurement
libraries to be loaded into specific sessions without an explicit
<command>LOAD</> command being given. For example, debugging could
be enabled for all sessions under a given user name by setting
this parameter with <command>ALTER ROLE SET</>.
</para>
<para>
If a specified library is not found,
the connection attempt will fail.
</para>
<para>
Every PostgreSQL-supported library has a <quote>magic
block</> that is checked to guarantee compatibility.
For this reason, non-PostgreSQL libraries cannot be
loaded in this way.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
</sect1>

2
src/backend/tcop/postgres.c
View File

@ -3743,7 +3743,7 @@ PostgresMain(int argc, char *argv[],
* process any libraries that should be preloaded at backend start (this
* likewise can't be done until GUC settings are complete)
*/
process_local_preload_libraries();
process_session_preload_libraries();
/*
* Send this backend's cancellation info to the frontend.

6
src/backend/utils/init/miscinit.c
View File

@ -1222,6 +1222,7 @@ ValidatePgVersion(const char *path)
* GUC variables: lists of library names to be preloaded at postmaster
* start and at backend start
*/
char *session_preload_libraries_string = NULL;
char *shared_preload_libraries_string = NULL;
char *local_preload_libraries_string = NULL;
@ -1318,8 +1319,11 @@ process_shared_preload_libraries(void)
* process any libraries that should be preloaded at backend start
*/
void
process_local_preload_libraries(void)
process_session_preload_libraries(void)
{
load_libraries(session_preload_libraries_string,
"session_preload_libraries",
false);
load_libraries(local_preload_libraries_string,
"local_preload_libraries",
true);

19
src/backend/utils/misc/guc.c
View File

@ -591,6 +591,8 @@ const char *const config_group_names[] =
gettext_noop("Client Connection Defaults / Statement Behavior"),
/* CLIENT_CONN_LOCALE */
gettext_noop("Client Connection Defaults / Locale and Formatting"),
/* CLIENT_CONN_PRELOAD */
gettext_noop("Client Connection Defaults / Shared Library Preloading"),
/* CLIENT_CONN_OTHER */
gettext_noop("Client Connection Defaults / Other Defaults"),
/* LOCK_MANAGEMENT */
@ -2770,7 +2772,18 @@ static struct config_string ConfigureNamesString[] =
},
{
{"shared_preload_libraries", PGC_POSTMASTER, RESOURCES_KERNEL,
{"session_preload_libraries", PGC_SUSET, CLIENT_CONN_PRELOAD,
gettext_noop("Lists shared libraries to preload into each backend."),
NULL,
GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY
},
&session_preload_libraries_string,
"",
NULL, NULL, NULL
},
{
{"shared_preload_libraries", PGC_POSTMASTER, CLIENT_CONN_PRELOAD,
gettext_noop("Lists shared libraries to preload into server."),
NULL,
GUC_LIST_INPUT | GUC_LIST_QUOTE | GUC_SUPERUSER_ONLY
@ -2781,8 +2794,8 @@ static struct config_string ConfigureNamesString[] =
},
{
{"local_preload_libraries", PGC_BACKEND, CLIENT_CONN_OTHER,
gettext_noop("Lists shared libraries to preload into each backend."),
{"local_preload_libraries", PGC_BACKEND, CLIENT_CONN_PRELOAD,
gettext_noop("Lists unprivileged shared libraries to preload into each backend."),
NULL,
GUC_LIST_INPUT | GUC_LIST_QUOTE
},

3
src/include/miscadmin.h
View File

@ -403,6 +403,7 @@ extern void BaseInit(void);
/* in utils/init/miscinit.c */
extern bool IgnoreSystemIndexes;
extern PGDLLIMPORT bool process_shared_preload_libraries_in_progress;
extern char *session_preload_libraries_string;
extern char *shared_preload_libraries_string;
extern char *local_preload_libraries_string;
@ -438,7 +439,7 @@ extern void TouchSocketLockFiles(void);
extern void AddToDataDirLockFile(int target_line, const char *str);
extern void ValidatePgVersion(const char *path);
extern void process_shared_preload_libraries(void);
extern void process_local_preload_libraries(void);
extern void process_session_preload_libraries(void);
extern void pg_bindtextdomain(const char *domain);
extern bool has_rolreplication(Oid roleid);

1
src/include/utils/guc_tables.h
View File

@ -88,6 +88,7 @@ enum config_group
CLIENT_CONN,
CLIENT_CONN_STATEMENT,
CLIENT_CONN_LOCALE,
CLIENT_CONN_PRELOAD,
CLIENT_CONN_OTHER,
LOCK_MANAGEMENT,
COMPAT_OPTIONS,