34.1. Database Connection Control Functions
The following functions deal with making a connection to a
PostgreSQL
backend server. An
application program can have several backend connections open at
one time. (One reason to do that is to access more than one
database.) Each connection is represented by a
PGconn
object, which
is obtained from the function
PQconnectdb
,
PQconnectdbParams
, or
PQsetdbLogin
. Note that these functions will always
return a non-null object pointer, unless perhaps there is too
little memory even to allocate the
PGconn
object.
The
PQstatus
function should be called to check
the return value for a successful connection before queries are sent
via the connection object.
Warning
If untrusted users have access to a database that has not adopted a
secure schema usage pattern
,
begin each session by removing publicly-writable schemas from
search_path
. One can set parameter key
word
options
to
value
-csearch_path=
. Alternately, one can
issue
PQexec(
after
connecting. This consideration is not specific
to
libpq
; it applies to every interface for
executing arbitrary SQL commands.
conn
, "SELECT
pg_catalog.set_config('search_path', '', false)")
Warning
On Unix, forking a process with open libpq connections can lead to
unpredictable results because the parent and child processes share
the same sockets and operating system resources. For this reason,
such usage is not recommended, though doing an
exec
from
the child process to load a new executable is safe.
-
PQconnectdbParams
-
Makes a new connection to the database server.
PGconn *PQconnectdbParams(const char * const *keywords, const char * const *values, int expand_dbname);
This function opens a new database connection using the parameters taken from two
NULL
-terminated arrays. The first,keywords
, is defined as an array of strings, each one being a key word. The second,values
, gives the value for each key word. UnlikePQsetdbLogin
below, the parameter set can be extended without changing the function signature, so use of this function (or its nonblocking analogsPQconnectStartParams
andPQconnectPoll
) is preferred for new application programming.The currently recognized parameter key words are listed in Section 34.1.2 .
The passed arrays can be empty to use all default parameters, or can contain one or more parameter settings. They must be matched in length. Processing will stop at the first
NULL
entry in thekeywords
array. Also, if thevalues
entry associated with a non-NULL
keywords
entry isNULL
or an empty string, that entry is ignored and processing continues with the next pair of array entries.When
expand_dbname
is non-zero, the value for the firstdbname
key word is checked to see if it is a connection string . If so, it is " expanded " into the individual connection parameters extracted from the string. The value is considered to be a connection string, rather than just a database name, if it contains an equal sign (=
) or it begins with a URI scheme designator. (More details on connection string formats appear in Section 34.1.1 .) Only the first occurrence ofdbname
is treated in this way; any subsequentdbname
parameter is processed as a plain database name.In general the parameter arrays are processed from start to end. If any key word is repeated, the last value (that is not
NULL
or empty) is used. This rule applies in particular when a key word found in a connection string conflicts with one appearing in thekeywords
array. Thus, the programmer may determine whether array entries can override or be overridden by values taken from a connection string. Array entries appearing before an expandeddbname
entry can be overridden by fields of the connection string, and in turn those fields are overridden by array entries appearing afterdbname
(but, again, only if those entries supply non-empty values).After processing all the array entries and any expanded connection string, any connection parameters that remain unset are filled with default values. If an unset parameter's corresponding environment variable (see Section 34.14 ) is set, its value is used. If the environment variable is not set either, then the parameter's built-in default value is used.
-
PQconnectdb
-
Makes a new connection to the database server.
PGconn *PQconnectdb(const char *conninfo);
This function opens a new database connection using the parameters taken from the string
conninfo
.The passed string can be empty to use all default parameters, or it can contain one or more parameter settings separated by whitespace, or it can contain a URI . See Section 34.1.1 for details.
-
PQsetdbLogin
-
Makes a new connection to the database server.
PGconn *PQsetdbLogin(const char *pghost, const char *pgport, const char *pgoptions, const char *pgtty, const char *dbName, const char *login, const char *pwd);
This is the predecessor of
PQconnectdb
with a fixed set of parameters. It has the same functionality except that the missing parameters will always take on default values. WriteNULL
or an empty string for any one of the fixed parameters that is to be defaulted.If the
dbName
contains an=
sign or has a valid connection URI prefix, it is taken as aconninfo
string in exactly the same way as if it had been passed toPQconnectdb
, and the remaining parameters are then applied as specified forPQconnectdbParams
. -
PQsetdb
-
Makes a new connection to the database server.
PGconn *PQsetdb(char *pghost, char *pgport, char *pgoptions, char *pgtty, char *dbName);
This is a macro that calls
PQsetdbLogin
with null pointers for thelogin
andpwd
parameters. It is provided for backward compatibility with very old programs. -
PQconnectStartParams
PQconnectStart
PQconnectPoll
-
Make a connection to the database server in a nonblocking manner.
PGconn *PQconnectStartParams(const char * const *keywords, const char * const *values, int expand_dbname); PGconn *PQconnectStart(const char *conninfo); PostgresPollingStatusType PQconnectPoll(PGconn *conn);
These three functions are used to open a connection to a database server such that your application's thread of execution is not blocked on remote I/O whilst doing so. The point of this approach is that the waits for I/O to complete can occur in the application's main loop, rather than down inside
PQconnectdbParams
orPQconnectdb
, and so the application can manage this operation in parallel with other activities.With
PQconnectStartParams
, the database connection is made using the parameters taken from thekeywords
andvalues
arrays, and controlled byexpand_dbname
, as described above forPQconnectdbParams
.With
PQconnectStart
, the database connection is made using the parameters taken from the stringconninfo
as described above forPQconnectdb
.Neither
PQconnectStartParams
norPQconnectStart
norPQconnectPoll
will block, so long as a number of restrictions are met:-
The
hostaddr
parameter must be used appropriately to prevent DNS queries from being made. See the documentation of this parameter in Section 34.1.2 for details. -
If you call
PQtrace
, ensure that the stream object into which you trace will not block. -
You must ensure that the socket is in the appropriate state before calling
PQconnectPoll
, as described below.
To begin a nonblocking connection request, call
PQconnectStart
orPQconnectStartParams
. If the result is null, then libpq has been unable to allocate a newPGconn
structure. Otherwise, a validPGconn
pointer is returned (though not yet representing a valid connection to the database). Next callPQstatus(conn)
. If the result isCONNECTION_BAD
, the connection attempt has already failed, typically because of invalid connection parameters.If
PQconnectStart
orPQconnectStartParams
succeeds, the next stage is to poll libpq so that it can proceed with the connection sequence. UsePQsocket(conn)
to obtain the descriptor of the socket underlying the database connection. (Caution: do not assume that the socket remains the same acrossPQconnectPoll
calls.) Loop thus: IfPQconnectPoll(conn)
last returnedPGRES_POLLING_READING
, wait until the socket is ready to read (as indicated byselect()
,poll()
, or similar system function). Then callPQconnectPoll(conn)
again. Conversely, ifPQconnectPoll(conn)
last returnedPGRES_POLLING_WRITING
, wait until the socket is ready to write, then callPQconnectPoll(conn)
again. On the first iteration, i.e., if you have yet to callPQconnectPoll
, behave as if it last returnedPGRES_POLLING_WRITING
. Continue this loop untilPQconnectPoll(conn)
returnsPGRES_POLLING_FAILED
, indicating the connection procedure has failed, orPGRES_POLLING_OK
, indicating the connection has been successfully made.At any time during connection, the status of the connection can be checked by calling
PQstatus
. If this call returnsCONNECTION_BAD
, then the connection procedure has failed; if the call returnsCONNECTION_OK
, then the connection is ready. Both of these states are equally detectable from the return value ofPQconnectPoll
, described above. Other states might also occur during (and only during) an asynchronous connection procedure. These indicate the current stage of the connection procedure and might be useful to provide feedback to the user for example. These statuses are:-
CONNECTION_STARTED
-
Waiting for connection to be made.
-
CONNECTION_MADE
-
Connection OK; waiting to send.
-
CONNECTION_AWAITING_RESPONSE
-
Waiting for a response from the server.
-
CONNECTION_AUTH_OK
-
Received authentication; waiting for backend start-up to finish.
-
CONNECTION_SSL_STARTUP
-
Negotiating SSL encryption.
-
CONNECTION_SETENV
-
Negotiating environment-driven parameter settings.
-
CONNECTION_CHECK_WRITABLE
-
Checking if connection is able to handle write transactions.
-
CONNECTION_CONSUME
-
Consuming any remaining response messages on connection.
Note that, although these constants will remain (in order to maintain compatibility), an application should never rely upon these occurring in a particular order, or at all, or on the status always being one of these documented values. An application might do something like this:
switch(PQstatus(conn)) { case CONNECTION_STARTED: feedback = "Connecting..."; break; case CONNECTION_MADE: feedback = "Connected to server..."; break; . . . default: feedback = "Connecting..."; }
The
connect_timeout
connection parameter is ignored when usingPQconnectPoll
; it is the application's responsibility to decide whether an excessive amount of time has elapsed. Otherwise,PQconnectStart
followed by aPQconnectPoll
loop is equivalent toPQconnectdb
.Note that when
PQconnectStart
orPQconnectStartParams
returns a non-null pointer, you must callPQfinish
when you are finished with it, in order to dispose of the structure and any associated memory blocks. This must be done even if the connection attempt fails or is abandoned. -
-
PQconndefaults
-
Returns the default connection options.
PQconninfoOption *PQconndefaults(void); typedef struct { char *keyword; /* The keyword of the option */ char *envvar; /* Fallback environment variable name */ char *compiled; /* Fallback compiled in default value */ char *val; /* Option's current value, or NULL */ char *label; /* Label for field in connect dialog */ char *dispchar; /* Indicates how to display this field in a connect dialog. Values are: "" Display entered value as is "*" Password field - hide value "D" Debug option - don't show by default */ int dispsize; /* Field size in characters for dialog */ } PQconninfoOption;
Returns a connection options array. This can be used to determine all possible
PQconnectdb
options and their current default values. The return value points to an array ofPQconninfoOption
structures, which ends with an entry having a nullkeyword
pointer. The null pointer is returned if memory could not be allocated. Note that the current default values (val
fields) will depend on environment variables and other context. A missing or invalid service file will be silently ignored. Callers must treat the connection options data as read-only.After processing the options array, free it by passing it to
PQconninfoFree
. If this is not done, a small amount of memory is leaked for each call toPQconndefaults
. -
PQconninfo
-
Returns the connection options used by a live connection.
PQconninfoOption *PQconninfo(PGconn *conn);
Returns a connection options array. This can be used to determine all possible
PQconnectdb
options and the values that were used to connect to the server. The return value points to an array ofPQconninfoOption
structures, which ends with an entry having a nullkeyword
pointer. All notes above forPQconndefaults
also apply to the result ofPQconninfo
. -
PQconninfoParse
-
Returns parsed connection options from the provided connection string.
PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);
Parses a connection string and returns the resulting options as an array; or returns
NULL
if there is a problem with the connection string. This function can be used to extract thePQconnectdb
options in the provided connection string. The return value points to an array ofPQconninfoOption
structures, which ends with an entry having a nullkeyword
pointer.All legal options will be present in the result array, but the
PQconninfoOption
for any option not present in the connection string will haveval
set toNULL
; default values are not inserted.If
errmsg
is notNULL
, then*errmsg
is set toNULL
on success, else to amalloc
'd error string explaining the problem. (It is also possible for*errmsg
to be set toNULL
and the function to returnNULL
; this indicates an out-of-memory condition.)After processing the options array, free it by passing it to
PQconninfoFree
. If this is not done, some memory is leaked for each call toPQconninfoParse
. Conversely, if an error occurs anderrmsg
is notNULL
, be sure to free the error string usingPQfreemem
. -
PQfinish
-
Closes the connection to the server. Also frees memory used by the
PGconn
object.void PQfinish(PGconn *conn);
Note that even if the server connection attempt fails (as indicated by
PQstatus
), the application should callPQfinish
to free the memory used by thePGconn
object. ThePGconn
pointer must not be used again afterPQfinish
has been called. -
PQreset
-
Resets the communication channel to the server.
void PQreset(PGconn *conn);
This function will close the connection to the server and attempt to establish a new connection, using all the same parameters previously used. This might be useful for error recovery if a working connection is lost.
-
PQresetStart
PQresetPoll
-
Reset the communication channel to the server, in a nonblocking manner.
int PQresetStart(PGconn *conn); PostgresPollingStatusType PQresetPoll(PGconn *conn);
These functions will close the connection to the server and attempt to establish a new connection, using all the same parameters previously used. This can be useful for error recovery if a working connection is lost. They differ from
PQreset
(above) in that they act in a nonblocking manner. These functions suffer from the same restrictions asPQconnectStartParams
,PQconnectStart
andPQconnectPoll
.To initiate a connection reset, call
PQresetStart
. If it returns 0, the reset has failed. If it returns 1, poll the reset usingPQresetPoll
in exactly the same way as you would create the connection usingPQconnectPoll
. -
PQpingParams
-
PQpingParams
reports the status of the server. It accepts connection parameters identical to those ofPQconnectdbParams
, described above. It is not necessary to supply correct user name, password, or database name values to obtain the server status; however, if incorrect values are provided, the server will log a failed connection attempt.PGPing PQpingParams(const char * const *keywords, const char * const *values, int expand_dbname);
The function returns one of the following values:
-
PQPING_OK
-
The server is running and appears to be accepting connections.
-
PQPING_REJECT
-
The server is running but is in a state that disallows connections (startup, shutdown, or crash recovery).
-
PQPING_NO_RESPONSE
-
The server could not be contacted. This might indicate that the server is not running, or that there is something wrong with the given connection parameters (for example, wrong port number), or that there is a network connectivity problem (for example, a firewall blocking the connection request).
-
PQPING_NO_ATTEMPT
-
No attempt was made to contact the server, because the supplied parameters were obviously incorrect or there was some client-side problem (for example, out of memory).
-
-
PQping
-
PQping
reports the status of the server. It accepts connection parameters identical to those ofPQconnectdb
, described above. It is not necessary to supply correct user name, password, or database name values to obtain the server status; however, if incorrect values are provided, the server will log a failed connection attempt.PGPing PQping(const char *conninfo);
The return values are the same as for
PQpingParams
.
34.1.1. Connection Strings
Several libpq functions parse a user-specified string to obtain connection parameters. There are two accepted formats for these strings: plain keyword/value strings and URIs. URIs generally follow RFC 3986 , except that multi-host connection strings are allowed as further described below.
34.1.1.1. Keyword/Value Connection Strings
In the keyword/value format, each parameter setting is in the form
keyword
=
value
, with space(s) between settings.
Spaces around a setting's equal sign are
optional. To write an empty value, or a value containing spaces, surround it
with single quotes, for example
keyword = 'a value'
.
Single quotes and backslashes within
a value must be escaped with a backslash, i.e.,
\'
and
\\
.
Example:
host=localhost port=5432 dbname=mydb connect_timeout=10
The recognized parameter key words are listed in Section 34.1.2 .
34.1.1.2. Connection URIs
The general form for a connection URI is:
postgresql://[userspec
@][hostspec
][/dbname
][?paramspec
] whereuserspec
is:user
[:password
] andhostspec
is: [host
][:port
][,...] andparamspec
is:name
=value
[&...]
The
URI
scheme designator can be either
postgresql://
or
postgres://
. Each
of the remaining
URI
parts is optional. The
following examples illustrate valid
URI
syntax:
postgresql:// postgresql://localhost postgresql://localhost:5433 postgresql://localhost/mydb postgresql://user@localhost postgresql://user:secret@localhost postgresql://other@localhost/otherdb?connect_timeout=10&application_name=myapp postgresql://host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp
Values that would normally appear in the hierarchical part of the URI can alternatively be given as named parameters. For example:
postgresql:///mydb?host=localhost&port=5433
All named parameters must match key words listed in
Section 34.1.2
, except that for compatibility
with JDBC connection
URI
s, instances
of
ssl=true
are translated into
sslmode=require
.
Percent-encoding may be used to include symbols with special meaning in any
of the
URI
parts, e.g., replace
=
with
%3D
.
The host part may be either a host name or an IP address. To specify an IPv6 address, enclose it in square brackets:
postgresql://[2001:db8::1234]/database
The host part is interpreted as described for the parameter host . In particular, a Unix-domain socket connection is chosen if the host part is either empty or looks like an absolute path name, otherwise a TCP/IP connection is initiated. Note, however, that the slash is a reserved character in the hierarchical part of the URI. So, to specify a non-standard Unix-domain socket directory, either omit the host part of the URI and specify the host as a named parameter, or percent-encode the path in the host part of the URI:
postgresql:///dbname?host=/var/lib/postgresql postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
It is possible to specify multiple host components, each with an optional
port component, in a single URI. A URI of the form
postgresql://host1:port1,host2:port2,host3:port3/
is equivalent to a connection string of the form
host=host1,host2,host3 port=port1,port2,port3
.
As further described below, each
host will be tried in turn until a connection is successfully established.
34.1.1.3. Specifying Multiple Hosts
It is possible to specify multiple hosts to connect to, so that they are
tried in the given order. In the Keyword/Value format, the
host
,
hostaddr
, and
port
options accept comma-separated
lists of values. The same number of elements must be given in each
option that is specified, such
that e.g., the first
hostaddr
corresponds to the first host name,
the second
hostaddr
corresponds to the second host name, and so
forth. As an exception, if only one
port
is specified, it
applies to all the hosts.
In the connection URI format, you can list multiple
host:port
pairs
separated by commas in the
host
component of the URI.
In either format, a single host name can translate to multiple network addresses. A common example of this is a host that has both an IPv4 and an IPv6 address.
When multiple hosts are specified, or when a single host name is translated to multiple addresses, all the hosts and addresses will be tried in order, until one succeeds. If none of the hosts can be reached, the connection fails. If a connection is established successfully, but authentication fails, the remaining hosts in the list are not tried.
If a password file is used, you can have different passwords for different hosts. All the other connection options are the same for every host in the list; it is not possible to e.g., specify different usernames for different hosts.
34.1.2. Parameter Key Words
The currently recognized parameter key words are:
-
host
-
Name of host to connect to. If a host name begins with a slash, it specifies Unix-domain communication rather than TCP/IP communication; the value is the name of the directory in which the socket file is stored. The default behavior when
host
is not specified, or is empty, is to connect to a Unix-domain socket in/tmp
(or whatever socket directory was specified when PostgreSQL was built). On machines without Unix-domain sockets, the default is to connect tolocalhost
.A comma-separated list of host names is also accepted, in which case each host name in the list is tried in order; an empty item in the list selects the default behavior as explained above. See Section 34.1.1.3 for details.
-
hostaddr
-
Numeric IP address of host to connect to. This should be in the standard IPv4 address format, e.g.,
172.28.40.9
. If your machine supports IPv6, you can also use those addresses. TCP/IP communication is always used when a nonempty string is specified for this parameter.Using
hostaddr
instead ofhost
allows the application to avoid a host name look-up, which might be important in applications with time constraints. However, a host name is required for GSSAPI or SSPI authentication methods, as well as forverify-full
SSL certificate verification. The following rules are used:-
If
host
is specified withouthostaddr
, a host name lookup occurs. (When usingPQconnectPoll
, the lookup occurs whenPQconnectPoll
first considers this host name, and it may causePQconnectPoll
to block for a significant amount of time.) -
If
hostaddr
is specified withouthost
, the value forhostaddr
gives the server network address. The connection attempt will fail if the authentication method requires a host name. -
If both
host
andhostaddr
are specified, the value forhostaddr
gives the server network address. The value forhost
is ignored unless the authentication method requires it, in which case it will be used as the host name.
Note that authentication is likely to fail if
host
is not the name of the server at network addresshostaddr
. Also, when bothhost
andhostaddr
are specified,host
is used to identify the connection in a password file (see Section 34.15 ).A comma-separated list of
hostaddr
values is also accepted, in which case each host in the list is tried in order. An empty item in the list causes the corresponding host name to be used, or the default host name if that is empty as well. See Section 34.1.1.3 for details.Without either a host name or host address, libpq will connect using a local Unix-domain socket; or on machines without Unix-domain sockets, it will attempt to connect to
localhost
. -
-
port
-
Port number to connect to at the server host, or socket file name extension for Unix-domain connections. If multiple hosts were given in the
host
orhostaddr
parameters, this parameter may specify a comma-separated list of ports of the same length as the host list, or it may specify a single port number to be used for all hosts. An empty string, or an empty item in a comma-separated list, specifies the default port number established when PostgreSQL was built. -
dbname
-
The database name. Defaults to be the same as the user name. In certain contexts, the value is checked for extended formats; see Section 34.1.1 for more details on those.
-
user
-
PostgreSQL user name to connect as. Defaults to be the same as the operating system name of the user running the application.
-
password
-
Password to be used if the server demands password authentication.
-
passfile
-
Specifies the name of the file used to store passwords (see Section 34.15 ). Defaults to
~/.pgpass
, or%APPDATA%\postgresql\pgpass.conf
on Microsoft Windows. (No error is reported if this file does not exist.) -
connect_timeout
-
Maximum wait for connection, in seconds (write as a decimal integer, e.g.,
10
). Zero, negative, or not specified means wait indefinitely. The minimum allowed timeout is 2 seconds, therefore a value of1
is interpreted as2
. This timeout applies separately to each host name or IP address. For example, if you specify two hosts andconnect_timeout
is 5, each host will time out if no connection is made within 5 seconds, so the total time spent waiting for a connection might be up to 10 seconds. -
client_encoding
-
This sets the
client_encoding
configuration parameter for this connection. In addition to the values accepted by the corresponding server option, you can useauto
to determine the right encoding from the current locale in the client (LC_CTYPE
environment variable on Unix systems). -
options
-
Specifies command-line options to send to the server at connection start. For example, setting this to
-c geqo=off
sets the session's value of thegeqo
parameter tooff
. Spaces within this string are considered to separate command-line arguments, unless escaped with a backslash (\
); write\\
to represent a literal backslash. For a detailed discussion of the available options, consult Chapter 19 . -
application_name
-
Specifies a value for the application_name configuration parameter.
-
fallback_application_name
-
Specifies a fallback value for the application_name configuration parameter. This value will be used if no value has been given for
application_name
via a connection parameter or thePGAPPNAME
environment variable. Specifying a fallback name is useful in generic utility programs that wish to set a default application name but allow it to be overridden by the user. -
keepalives
-
Controls whether client-side TCP keepalives are used. The default value is 1, meaning on, but you can change this to 0, meaning off, if keepalives are not wanted. This parameter is ignored for connections made via a Unix-domain socket.
-
keepalives_idle
-
Controls the number of seconds of inactivity after which TCP should send a keepalive message to the server. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPIDLE
or an equivalent socket option is available, and on Windows; on other systems, it has no effect. -
keepalives_interval
-
Controls the number of seconds after which a TCP keepalive message that is not acknowledged by the server should be retransmitted. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPINTVL
or an equivalent socket option is available, and on Windows; on other systems, it has no effect. -
keepalives_count
-
Controls the number of TCP keepalives that can be lost before the client's connection to the server is considered dead. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket, or if keepalives are disabled. It is only supported on systems where
TCP_KEEPCNT
or an equivalent socket option is available; on other systems, it has no effect. -
tty
-
Ignored (formerly, this specified where to send server debug output).
-
replication
-
This option determines whether the connection should use the replication protocol instead of the normal protocol. This is what PostgreSQL replication connections as well as tools such as pg_basebackup use internally, but it can also be used by third-party applications. For a description of the replication protocol, consult Section 53.4 .
The following values, which are case-insensitive, are supported:
-
true
,on
,yes
,1
-
The connection goes into physical replication mode.
-
database
-
The connection goes into logical replication mode, connecting to the database specified in the
dbname
parameter. -
false
,off
,no
,0
-
The connection is a regular one, which is the default behavior.
In physical or logical replication mode, only the simple query protocol can be used.
-
-
sslmode
-
This option determines whether or with what priority a secure SSL TCP/IP connection will be negotiated with the server. There are six modes:
-
disable
-
only try a non- SSL connection
-
allow
-
first try a non- SSL connection; if that fails, try an SSL connection
-
prefer
(default) -
first try an SSL connection; if that fails, try a non- SSL connection
-
require
-
only try an SSL connection. If a root CA file is present, verify the certificate in the same way as if
verify-ca
was specified -
verify-ca
-
only try an SSL connection, and verify that the server certificate is issued by a trusted certificate authority ( CA )
-
verify-full
-
only try an SSL connection, verify that the server certificate is issued by a trusted CA and that the requested server host name matches that in the certificate
See Section 34.18 for a detailed description of how these options work.
sslmode
is ignored for Unix domain socket communication. If PostgreSQL is compiled without SSL support, using optionsrequire
,verify-ca
, orverify-full
will cause an error, while optionsallow
andprefer
will be accepted but libpq will not actually attempt an SSL connection. -
-
requiressl
-
This option is deprecated in favor of the
sslmode
setting.If set to 1, an SSL connection to the server is required (this is equivalent to
sslmode
require
). libpq will then refuse to connect if the server does not accept an SSL connection. If set to 0 (default), libpq will negotiate the connection type with the server (equivalent tosslmode
prefer
). This option is only available if PostgreSQL is compiled with SSL support. -
sslcompression
-
If set to 1, data sent over SSL connections will be compressed. If set to 0, compression will be disabled. The default is 0. This parameter is ignored if a connection without SSL is made.
SSL compression is nowadays considered insecure and its use is no longer recommended. OpenSSL 1.1.0 disables compression by default, and many operating system distributions disable it in prior versions as well, so setting this parameter to on will not have any effect if the server does not accept compression. On the other hand, OpenSSL before 1.0.0 does not support disabling compression, so this parameter is ignored with those versions, and whether compression is used depends on the server.
If security is not a primary concern, compression can improve throughput if the network is the bottleneck. Disabling compression can improve response time and throughput if CPU performance is the limiting factor.
-
sslcert
-
This parameter specifies the file name of the client SSL certificate, replacing the default
~/.postgresql/postgresql.crt
. This parameter is ignored if an SSL connection is not made. -
sslkey
-
This parameter specifies the location for the secret key used for the client certificate. It can either specify a file name that will be used instead of the default
~/.postgresql/postgresql.key
, or it can specify a key obtained from an external " engine " (engines are OpenSSL loadable modules). An external engine specification should consist of a colon-separated engine name and an engine-specific key identifier. This parameter is ignored if an SSL connection is not made. -
sslrootcert
-
This parameter specifies the name of a file containing SSL certificate authority ( CA ) certificate(s). If the file exists, the server's certificate will be verified to be signed by one of these authorities. The default is
~/.postgresql/root.crt
. -
sslcrl
-
This parameter specifies the file name of the SSL certificate revocation list (CRL). Certificates listed in this file, if it exists, will be rejected while attempting to authenticate the server's certificate. The default is
~/.postgresql/root.crl
. -
requirepeer
-
This parameter specifies the operating-system user name of the server, for example
requirepeer=postgres
. When making a Unix-domain socket connection, if this parameter is set, the client checks at the beginning of the connection that the server process is running under the specified user name; if it is not, the connection is aborted with an error. This parameter can be used to provide server authentication similar to that available with SSL certificates on TCP/IP connections. (Note that if the Unix-domain socket is in/tmp
or another publicly writable location, any user could start a server listening there. Use this parameter to ensure that you are connected to a server run by a trusted user.) This option is only supported on platforms for which thepeer
authentication method is implemented; see Section 20.9 . -
krbsrvname
-
Kerberos service name to use when authenticating with GSSAPI. This must match the service name specified in the server configuration for Kerberos authentication to succeed. (See also Section 20.6 .)
-
gsslib
-
GSS library to use for GSSAPI authentication. Currently this is disregarded except on Windows builds that include both GSSAPI and SSPI support. In that case, set this to
gssapi
to cause libpq to use the GSSAPI library for authentication instead of the default SSPI. -
service
-
Service name to use for additional parameters. It specifies a service name in
pg_service.conf
that holds additional connection parameters. This allows applications to specify only a service name so connection parameters can be centrally maintained. See Section 34.16 . -
target_session_attrs
-
If this parameter is set to
read-write
, only a connection in which read-write transactions are accepted by default is considered acceptable. The querySHOW transaction_read_only
will be sent upon any successful connection; if it returnson
, the connection will be closed. If multiple hosts were specified in the connection string, any remaining servers will be tried just as if the connection attempt had failed. The default value of this parameter,any
, regards all connections as acceptable.