All parameter names are case-insensitive. Every parameter takes a value of one of five types: boolean, string, integer, floating point, or enumerated (enum). The type determines the syntax for setting the parameter:
Boolean:
Values can be written as
on,
off,
true,
false,
yes,
no,
1,
0
(all case-insensitive) or any unambiguous prefix of one of these.
String: In general, enclose the value in single quotes, doubling any single quotes within the value. Quotes can usually be omitted if the value is a simple number or identifier, however. (Values that match a SQL keyword require quoting in some contexts.)
Numeric (integer and floating point):
Numeric parameters can be specified in the customary integer and
floating-point formats; fractional values are rounded to the nearest
integer if the parameter is of integer type. Integer parameters
additionally accept hexadecimal input (beginning
with 0x) and octal input (beginning
with 0), but these formats cannot have a fraction.
Do not use thousands separators.
Quotes are not required, except for hexadecimal input.
Numeric with Unit:
Some numeric parameters have an implicit unit, because they describe
quantities of memory or time. The unit might be bytes, kilobytes, blocks
(typically eight kilobytes), milliseconds, seconds, or minutes.
An unadorned numeric value for one of these settings will use the
setting's default unit, which can be learned from
pg_settings.unit.
For convenience, settings can be given with a unit specified explicitly,
for example '120 ms' for a time value, and they will be
converted to whatever the parameter's actual unit is. Note that the
value must be written as a string (with quotes) to use this feature.
The unit name is case-sensitive, and there can be whitespace between
the numeric value and the unit.
Valid memory units are B (bytes),
kB (kilobytes),
MB (megabytes), GB
(gigabytes), and TB (terabytes).
The multiplier for memory units is 1024, not 1000.
Valid time units are
us (microseconds),
ms (milliseconds),
s (seconds), min (minutes),
h (hours), and d (days).
If a fractional value is specified with a unit, it will be rounded
to a multiple of the next smaller unit if there is one.
For example, 30.1 GB will be converted
to 30822 MB not 32319628902 B.
If the parameter is of integer type, a final rounding to integer
occurs after any unit conversion.
Enumerated:
Enumerated-type parameters are written in the same way as string
parameters, but are restricted to have one of a limited set of
values. The values allowable for such a parameter can be found from
pg_settings.enumvals.
Enum parameter values are case-insensitive.
The most fundamental way to set these parameters is to edit the file
lightdb.conf,
which is normally kept in the data directory. A default copy is
installed when the database cluster directory is initialized.
An example of what this file might look like is:
# This is a comment log_connections = yes log_destination = 'syslog' search_path = '"$user", public' shared_buffers = 128MB
One parameter is specified per line. The equal sign between name and
value is optional. Whitespace is insignificant (except within a quoted
parameter value) and blank lines are
ignored. Hash marks (#) designate the remainder
of the line as a comment. Parameter values that are not simple
identifiers or numbers must be single-quoted. To embed a single
quote in a parameter value, write either two quotes (preferred)
or backslash-quote.
If the file contains multiple entries for the same parameter,
all but the last one are ignored.
Parameters set in this way provide default values for the cluster. The settings seen by active sessions will be these values unless they are overridden. The following sections describe ways in which the administrator or user can override these defaults.
The configuration file is reread whenever the main server process
receives a SIGHUP signal; this signal is most easily
sent by running lt_ctl reload from the command line or by
calling the SQL function pg_reload_conf(). The main
server process also propagates this signal to all currently running
server processes, so that existing sessions also adopt the new values
(this will happen after they complete any currently-executing client
command). Alternatively, you can
send the signal to a single server process directly. Some parameters
can only be set at server start; any changes to their entries in the
configuration file will be ignored until the server is restarted.
Invalid parameter settings in the configuration file are likewise
ignored (but logged) during SIGHUP processing.
In addition to lightdb.conf,
a LightDB data directory contains a file
lightdb.auto.conf,
which has the same format as lightdb.conf but
is intended to be edited automatically, not manually. This file holds
settings provided through the ALTER SYSTEM command.
This file is read whenever lightdb.conf is,
and its settings take effect in the same way. Settings
in lightdb.auto.conf override those
in lightdb.conf.
External tools may also
modify lightdb.auto.conf. It is not
recommended to do this while the server is running, since a
concurrent ALTER SYSTEM command could overwrite
such changes. Such tools might simply append new settings to the end,
or they might choose to remove duplicate settings and/or comments
(as ALTER SYSTEM will).
The system view
pg_file_settings
can be helpful for pre-testing changes to the configuration files, or for
diagnosing problems if a SIGHUP signal did not have the
desired effects.
LightDB provides three SQL
commands to establish configuration defaults.
The already-mentioned ALTER SYSTEM command
provides a SQL-accessible means of changing global defaults; it is
functionally equivalent to editing lightdb.conf.
In addition, there are two commands that allow setting of defaults
on a per-database or per-role basis:
The ALTER DATABASE command allows global settings to be overridden on a per-database basis.
The ALTER ROLE command allows both global and per-database settings to be overridden with user-specific values.
Values set with ALTER DATABASE and ALTER ROLE
are applied only when starting a fresh database session. They
override values obtained from the configuration files or server
command line, and constitute defaults for the rest of the session.
Note that some settings cannot be changed after server start, and
so cannot be set with these commands (or the ones listed below).
The above three methods of modifying parameters will be recorded in detail in the log
file(located in $LTDATA/log/), including the values before and after parameter
modification, as well as the time of parameter modification, client program name to
modify the parameter, user who modified the parameter, and specific SQL statements
used to modify the parameter. Also the old and current value of the modified parameter
will be prompted in the client program when issuing ALTER SYSTEM, ALTER DATABASE or ALTER ROLE.
Once a client is connected to the database, LightDB provides two additional SQL commands (and equivalent functions) to interact with session-local configuration settings:
The SHOW command allows inspection of the
current value of any parameter. The corresponding SQL function is
current_setting(setting_name text)
(see Section 9.27.1).
The SET command allows modification of the
current value of those parameters that can be set locally to a
session; it has no effect on other sessions.
The corresponding SQL function is
set_config(setting_name, new_value, is_local)
(see Section 9.27.1).
In addition, the system view pg_settings can be
used to view and change session-local values:
Querying this view is similar to using SHOW ALL but
provides more detail. It is also more flexible, since it's possible
to specify filter conditions or join against other relations.
Using UPDATE on this view, specifically
updating the setting column, is the equivalent
of issuing SET commands. For example, the equivalent of
SET configuration_parameter TO DEFAULT;
is:
UPDATE pg_settings SET setting = reset_val WHERE name = 'configuration_parameter';
In addition to setting global defaults or attaching overrides at the database or role level, you can pass settings to LightDB via shell facilities. Both the server and libpq client library accept parameter values via the shell.
During server startup, parameter settings can be
passed to the lightdb command via the
-c command-line parameter. For example,
lightdb -c log_connections=yes -c log_destination='syslog'
Settings provided in this way override those set via
lightdb.conf or ALTER SYSTEM,
so they cannot be changed globally without restarting the server.
When starting a client session via libpq,
parameter settings can be
specified using the LTOPTIONS environment variable.
Settings established in this way constitute defaults for the life
of the session, but do not affect other sessions.
For historical reasons, the format of LTOPTIONS is
similar to that used when launching the lightdb
command; specifically, the -c flag must be specified.
For example,
env PGOPTIONS="-c geqo=off -c statement_timeout=5min" ltsql
Other clients and libraries might provide their own mechanisms, via the shell or otherwise, that allow the user to alter session settings without direct use of SQL commands.
LightDB provides several features for breaking
down complex lightdb.conf files into sub-files.
These features are especially useful when managing multiple servers
with related, but not identical, configurations.
In addition to individual parameter settings,
the lightdb.conf file can contain include
directives, which specify another file to read and process as if
it were inserted into the configuration file at this point. This
feature allows a configuration file to be divided into physically
separate parts. Include directives simply look like:
include 'filename'
If the file name is not an absolute path, it is taken as relative to the directory containing the referencing configuration file. Inclusions can be nested.
There is also an include_if_exists directive, which acts
the same as the include directive, except
when the referenced file does not exist or cannot be read. A regular
include will consider this an error condition, but
include_if_exists merely logs a message and continues
processing the referencing configuration file.
The lightdb.conf file can also contain
include_dir directives, which specify an entire
directory of configuration files to include. These look like
include_dir 'directory'
Non-absolute directory names are taken as relative to the directory
containing the referencing configuration file. Within the specified
directory, only non-directory files whose names end with the
suffix .conf will be included. File names that
start with the . character are also ignored, to
prevent mistakes since such files are hidden on some platforms. Multiple
files within an include directory are processed in file name order
(according to C locale rules, i.e., numbers before letters, and
uppercase letters before lowercase ones).
Include files or directories can be used to logically separate portions
of the database configuration, rather than having a single large
lightdb.conf file. Consider a company that has two
database servers, each with a different amount of memory. There are
likely elements of the configuration both will share, for things such
as logging. But memory-related parameters on the server will vary
between the two. And there might be server specific customizations,
too. One way to manage this situation is to break the custom
configuration changes for your site into three files. You could add
this to the end of your lightdb.conf file to include
them:
include 'shared.conf' include 'memory.conf' include 'server.conf'
All systems would have the same shared.conf. Each
server with a particular amount of memory could share the
same memory.conf; you might have one for all servers
with 8GB of RAM, another for those having 16GB. And
finally server.conf could have truly server-specific
configuration information in it.
Another possibility is to create a configuration file directory and
put this information into files there. For example, a conf.d
directory could be referenced at the end of lightdb.conf:
include_dir 'conf.d'
Then you could name the files in the conf.d directory
like this:
00shared.conf 01memory.conf 02server.conf
This naming convention establishes a clear order in which these
files will be loaded. This is important because only the last
setting encountered for a particular parameter while the server is
reading configuration files will be used. In this example,
something set in conf.d/02server.conf would override a
value set in conf.d/01memory.conf.
You might instead use this approach to naming the files descriptively:
00shared.conf 01memory-8GB.conf 02server-foo.conf
This sort of arrangement gives a unique name for each configuration file variation. This can help eliminate ambiguity when several servers have their configurations all stored in one place, such as in a version control repository. (Storing database configuration files under version control is another good practice to consider.)