35.1. Database Connection Control Functions
The following functions deal with making a connection to a Postgres Pro 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 35.1.2.
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 35.1.1.) 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 35.15) 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 35.1.1 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
.pgtty
is no longer used and any value passed will be ignored.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 35.1.2 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
.PQsetSSLKeyPassHook_OpenSSL
PQsetSSLKeyPassHook_OpenSSL
lets an application override libpq's default handling of encrypted client certificate key files using sslpassword or interactive prompting.void PQsetSSLKeyPassHook_OpenSSL(PQsslKeyPassHook_OpenSSL_type hook);
The application passes a pointer to a callback function with signature:
int callback_fn(char *buf, int size, PGconn *conn);
which libpq will then call instead of its default
PQdefaultSSLKeyPassHook_OpenSSL
handler. The callback should determine the password for the key and copy it to result-bufferbuf
of sizesize
. The string inbuf
must be null-terminated. The callback must return the length of the password stored inbuf
excluding the null terminator. On failure, the callback should setbuf[0] = '\0'
and return 0.If the user specified an explicit key location, its path will be in
conn->sslkey
when the callback is invoked. This will be empty if the default key path is being used. For keys that are engine specifiers, it is up to engine implementations whether they use the OpenSSL password callback or define their own handling.The app callback may choose to delegate unhandled cases to
PQdefaultSSLKeyPassHook_OpenSSL
, or call it first and try something else if it returns 0, or completely override it.The callback must not escape normal flow control with exceptions,
longjmp(...)
, etc. It must return normally.PQgetSSLKeyPassHook_OpenSSL
PQgetSSLKeyPassHook_OpenSSL
returns the current client certificate key password hook, orNULL
if none has been set.PQsslKeyPassHook_OpenSSL_type PQgetSSLKeyPassHook_OpenSSL(void);
35.1.1. 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.
35.1.1.1. 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 35.1.2.
35.1.1.2. 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?hostorder=random&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 35.1.2, except that for compatibility with JDBC connection URIs, instances of ssl=true
are translated into sslmode=require
.
The connection URI needs to be encoded with percent-encoding if it includes symbols with special meaning in any of its parts. Here is an example where the equal sign (=
) is replaced with %3D
and the space character with %20
:
postgresql://user@localhost:5433/mydb?options=-c%20synchronous_commit%3Doff
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
. Each host will be tried in the order defined by the hostorder parameter until a connection is successfully established, all hosts have been tried, or failover_timeout is reached. For details, see Section 35.1.1.3.
35.1.1.3. Specifying Multiple Hosts
It is possible to specify multiple hosts to connect to. In the Keyword/Value format, the host
, hostaddr
, and port
options accept a comma-separated list 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 the order defined by the hostorder parameter until one succeeds. By default, each host is tried only once. You can allow multiple connection attempts to each host using the failover_timeout parameter, which specifies the maximum time for making a connection. 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.
35.1.2. Parameter Key Words
The currently recognized parameter key words are:
host
Name of host to connect to. If a host name looks like an absolute path name, 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. (On Unix, an absolute path name begins with a slash. On Windows, paths starting with drive letters are also recognized.) If the host name starts with
@
, it is taken as a Unix-domain socket in the abstract namespace (currently supported on Linux and Windows). The default behavior whenhost
is not specified, or is empty, is to connect to a Unix-domain socket in/tmp
(or whatever socket directory was specified when Postgres Pro was built). On Windows and 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 the order defined by the hostorder parameter; an empty item in the list selects the default behavior as explained above. See Section 35.1.1.3 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. If this parameter is not specified, the value ofhost
will be looked up to find the corresponding IP address — or, ifhost
specifies an IP address, that value will be used directly.Using
hostaddr
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 35.16).A comma-separated list of
hostaddr
values is also accepted, in which case each host in the list is tried in the order defined by the hostorder parameter. 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 35.1.1.3 for details.Without either a host name or host address, libpq will connect using a local Unix-domain socket; or on Windows and on machines without Unix-domain sockets, it will attempt to connect to
localhost
.hostorder
Defines the order of connecting to the hosts specified by the host or hostaddr parameter.
If the value of this parameter is
sequential
(the default), connections to the hosts are attempted in the order in which the hosts are listed.If the value is
random
, the host to connect to is randomly picked from the list. This setting can help you balance the load between several cluster nodes instead of always connecting to the first available host in the list. You can also use the target_session_attrs parameter to forbid read-only connections.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 Postgres Pro 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 35.1.1 for more details on those.
user
Postgres Pro 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 35.16). Defaults to
~/.pgpass
, or%APPDATA%\postgresql\pgpass.conf
on Microsoft Windows. (No error is reported if this file does not exist.)channel_binding
This option controls the client's use of channel binding. A setting of
require
means that the connection must employ channel binding,prefer
means that the client will choose channel binding if available, anddisable
prevents the use of channel binding. The default isprefer
if Postgres Pro is compiled with SSL support; otherwise the default isdisable
.Channel binding is a method for the server to authenticate itself to the client. It is only supported over SSL connections with Postgres Pro 11 or later servers using the
SCRAM
authentication method.reusepass
Specifies whether reusing the prompted password is allowed when reestablishing connections. To forbid password reuse, set
reusepass
to0
. You can use this option together with idle_session_timeout to define the reconnection behavior for sessions terminated by timeout.Default:
1
connect_timeout
Maximum time to wait while connecting, 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.failover_timeout
Maximum time, in seconds, to cyclically retry to connect to the hosts specified in the connection string. If this parameter is not set (the default), connection to each host is tried only once. The specified value must be a decimal integer number.
When using this parameter in clusters with master-standby replication, make sure that its value provides enough time for a standby node to become the new master if the current master node fails. In this case, clients will be able to reconnect to the new master once failover is complete.
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.tcp_user_timeout
Controls the number of milliseconds that transmitted data may remain unacknowledged before a connection is forcibly closed. A value of zero uses the system default. This parameter is ignored for connections made via a Unix-domain socket. It is only supported on systems where
TCP_USER_TIMEOUT
is available; on other systems, it has no effect.replication
This option determines whether the connection should use the replication protocol instead of the normal protocol. This is what Postgres Pro 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 54.4.
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.
-
gssencmode
This option determines whether or with what priority a secure GSS TCP/IP connection will be negotiated with the server. There are three modes:
disable
only try a non-GSSAPI-encrypted connection
prefer
(default)if there are GSSAPI credentials present (i.e., in a credentials cache), first try a GSSAPI-encrypted connection; if that fails or there are no credentials, try a non-GSSAPI-encrypted connection. This is the default when Postgres Pro has been compiled with GSSAPI support.
require
only try a GSSAPI-encrypted connection
gssencmode
is ignored for Unix domain socket communication. If Postgres Pro is compiled without GSSAPI support, using therequire
option will cause an error, whileprefer
will be accepted but libpq will not actually attempt a GSSAPI-encrypted connection.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 specifiedverify-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 35.19 for a detailed description of how these options work.
sslmode
is ignored for Unix domain socket communication. If Postgres Pro 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.Note that if GSSAPI encryption is possible, that will be used in preference to SSL encryption, regardless of the value of
sslmode
. To force use of SSL encryption in an environment that has working GSSAPI infrastructure (such as a Kerberos server), also setgssencmode
todisable
.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 Postgres Pro 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. Postgres Pro 14 disables compression completely in the backend.
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.sslpassword
This parameter specifies the password for the secret key specified in
sslkey
, allowing client certificate private keys to be stored in encrypted form on disk even when interactive passphrase input is not practical.Specifying this parameter with any non-empty value suppresses the
Enter PEM pass phrase:
prompt that OpenSSL will emit by default when an encrypted client certificate key is provided tolibpq
.If the key is not encrypted this parameter is ignored. The parameter has no effect on keys specified by OpenSSL engines unless the engine uses the OpenSSL password callback mechanism for prompts.
There is no environment variable equivalent to this option, and no facility for looking it up in
.pgpass
. It can be used in a service file connection definition. Users with more sophisticated uses should consider using OpenSSL engines and tools like PKCS#11 or USB crypto offload devices.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 server certificate revocation list (CRL). Certificates listed in this file, if it exists, will be rejected while attempting to authenticate the server's certificate. If neither sslcrl nor sslcrldir is set, this setting is taken as
~/.postgresql/root.crl
.sslcrldir
This parameter specifies the directory name of the SSL server certificate revocation list (CRL). Certificates listed in the files in this directory, if it exists, will be rejected while attempting to authenticate the server's certificate.
The directory needs to be prepared with the OpenSSL command
openssl rehash
orc_rehash
. See its documentation for details.Both
sslcrl
andsslcrldir
can be specified together.sslsni
If set to 1 (default), libpq sets the TLS extension “Server Name Indication” (SNI) on SSL-enabled connections. By setting this parameter to 0, this is turned off.
The Server Name Indication can be used by SSL-aware proxies to route connections without having to decrypt the SSL stream. (Note that this requires a proxy that is aware of the PostgreSQL protocol handshake, not just any SSL proxy.) However, SNI makes the destination host name appear in cleartext in the network traffic, so it might be undesirable in some cases.
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.ssl_min_protocol_version
This parameter specifies the minimum SSL/TLS protocol version to allow for the connection. Valid values are
TLSv1
,TLSv1.1
,TLSv1.2
andTLSv1.3
. The supported protocols depend on the version of OpenSSL used, older versions not supporting the most modern protocol versions. If not specified, the default isTLSv1.2
, which satisfies industry best practices as of this writing.ssl_max_protocol_version
This parameter specifies the maximum SSL/TLS protocol version to allow for the connection. Valid values are
TLSv1
,TLSv1.1
,TLSv1.2
andTLSv1.3
. The supported protocols depend on the version of OpenSSL used, older versions not supporting the most modern protocol versions. If not set, this parameter is ignored and the connection will use the maximum bound defined by the backend, if set. Setting the maximum protocol version is mainly useful for testing or if some component has issues working with a newer protocol.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.) The default value is normally
postgres
, but that can be changed when building Postgres Pro via the--with-krb-srvnam
option of configure. In most environments, this parameter never needs to be changed. Some Kerberos implementations might require a different service name, such as Microsoft Active Directory which requires the service name to be in upper case (POSTGRES
).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 35.17.target_session_attrs
This option determines whether the session must have certain properties to be acceptable. It's typically used in combination with multiple host names to select the first acceptable alternative among several hosts. There are six modes:
any
(default)any successful connection is acceptable
read-write
session must accept read-write transactions by default (that is, the server must not be in hot standby mode and the
default_transaction_read_only
parameter must beoff
)read-only
session must not accept read-write transactions by default (the converse)
primary
server must not be in hot standby mode
standby
server must be in hot standby mode
prefer-standby
first try to find a standby server, but if none of the listed hosts is a standby server, try again in
any
mode
target_server_type
Same as target_session_attrs. This parameter is provided for backward compatibility with Postgres Pro Enterprise 9.6.