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    pg_connect

    (PHP 4, PHP 5, PHP 7, PHP 8)

    pg_connect — Open a PostgreSQL connection

    Description

    pg_connect(string $connection_string, int $flags = 0): PgSql\Connection|false

    pg_connect() opens a connection to a PostgreSQL database specified by the connection_string.

    If a second call is made to pg_connect() with the same connection_string as an existing connection, the existing connection will be returned unless you pass PGSQL_CONNECT_FORCE_NEW as flags.

    The old syntax with multiple parameters $conn = pg_connect("host", "port", "options", "tty", "dbname") has been deprecated.

    Parameters

    connection_string

    The connection_string can be empty to use all default parameters, or it can contain one or more parameter settings separated by whitespace. Each parameter setting is in the form keyword = value. Spaces around the equal sign are optional. To write an empty value or a value containing spaces, surround it with single quotes, e.g., keyword = 'a value'. Single quotes and backslashes within the value must be escaped with a backslash, i.e., \' and \\.

    The currently recognized parameter keywords are: host, hostaddr, port, dbname (defaults to value of user), user, password, connect_timeout, options, tty (ignored), sslmode, requiressl (deprecated in favor of sslmode), and service. Which of these arguments exist depends on your PostgreSQL version.

    The options parameter can be used to set command line parameters to be invoked by the server.

    flags

    If PGSQL_CONNECT_FORCE_NEW is passed, then a new connection is created, even if the connection_string is identical to an existing connection.

    If PGSQL_CONNECT_ASYNC is given, then the connection is established asynchronously. The state of the connection can then be checked via pg_connect_poll() or pg_connection_status().

    Return Values

    Returns an PgSql\Connection instance on success, or false on failure.

    Changelog

    Version Description
    8.1.0 Returns an PgSql\Connection instance now; previously, a resource was returned.

    Examples

    Example #1 Using pg_connect()

    <?php
    $dbconn     = pg_connect("dbname=mary");
    //connect to a database named "mary"

    $dbconn2 = pg_connect("host=localhost port=5432 dbname=mary");
    // connect to a database named "mary" on "localhost" at port "5432"

    $dbconn3 = pg_connect("host=sheep port=5432 dbname=mary user=lamb password=foo");
    //connect to a database named "mary" on the host "sheep" with a username and password

    $conn_string = "host=sheep port=5432 dbname=test user=lamb password=bar";
    $dbconn4 = pg_connect($conn_string);
    //connect to a database named "test" on the host "sheep" with a username and password

    $dbconn5 = pg_connect("host=localhost options='--client_encoding=UTF8'");
    //connect to a database on "localhost" and set the command line parameter which tells the encoding is in UTF-8
    ?>

    See Also

    • pg_pconnect() - Open a persistent PostgreSQL connection
    • pg_close() - Closes a PostgreSQL connection
    • pg_host() - Returns the host name associated with the connection
    • pg_port() - Return the port number associated with the connection
    • pg_tty() - Return the TTY name associated with the connection
    • pg_options() - Get the options associated with the connection
    • pg_dbname() - Get the database name

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    User Contributed Notes 20 notes

    up
    13
    lukasz dot wolczak at gmail dot com
    8 years ago
    It is worth to know, that you can set application_name in connection string, consider this simple example:

    <?php
    $appName     = $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
    $connStr = "host=localhost port=5432 dbname=postgres user=postgres options='--application_name=$appName'";

    //simple check
    $conn = pg_connect($connStr);
    $result = pg_query($conn, "select * from pg_stat_activity");
    var_dump(pg_fetch_all($result));

    ?>

    By doing this move on cli or cgi you can see in pgAdmin what scripts are running or what requests are running on database. You can extend configuration of postgres to track slow queries and print application name to logs. It was very usuful to me to find out what and where should I optimize.
    up
    6
    Dave
    11 years ago
    If you use pgbouncer and unix socket
    and you pgbouncer.ini looks like this
    listen_port = 6432
    unix_socket_dir = /tmp

    you connect like this

    pg_connect('host=/tmp port=6432 dbname=DB user=USER password=PASS');
    up
    4
    Anonymous
    10 years ago
    Getting md5 passwords was confusing because of a lack of documentation:

    - set up your pg_hba.conf in order to use md5 password instead of 'trust' or 'ident'
    - check if your postgres.conf has 'password_encryption=on' (depending on the version this might already be 'on').
    - make sure to restart your postgres process.
    - in PHP you just supply the username and password in _plain_ text:
    'host=localhost port=5432 dbname=megadb user=megauser password=holyhandbagsbatmanthispasswordisinplaintext'
    The postgres PHP library will automagically do the md5 encoding for you, no need to do it yourself.
    up
    3
    bgalloway at citycarshare dot org
    16 years ago
    Beware about writing something like
    <?php
    function getdb_FAILS() {
    return     pg_connect("...") or die('connection failed');
    }
    ?>

    It will return a boolean. This will appear to be fine if you don't use the return value as a db connection handle, but will fail if you do.

    Instead, use:
    <?php
    function getdb() {
    $db = pg_connect("...") or die('connection failed');
    return     $db;
    }
    ?>

    which actually returns a handle.
    up
    2
    tim at buttersideup dot com
    16 years ago
    It's not explicitly stated here, but you can also connect to PostgreSQL via a UNIX domain socket by leaving the host empty. This should have less overhead than using TCP e.g.:

    $dbh = new PDO('pgsql:user=exampleuser dbname=exampledb password=examplepass');

    In fact as the C library call PQconnectdb underlies this implementation, you can supply anything that this library call would take - the "pgsql:" prefix gets stripped off before PQconnectdb is called, and if you supply any of the optional arguments (e.g. user), then these arguments will be added to the string that you supplied... Check the docs for your relevant PostgreSQL client library: e.g.

    http://www.postgresql.org/docs/8.3/static/libpq-connect.html

    If you really want, you can use ';'s to separate your arguments - these will just be converted to spaces before PQconnectdb is called.

    Tim.
    up
    2
    thakur at corexprts dot com
    14 years ago
    One thing is to remember, whenever trying to use pg_connect, add the timeout parameter with it

    <?php
    $d    =pg_connect('host=example.com user=pgsql dbname=postgres connect_timeout=5');
    ?>
    up
    1
    matias at nospam dot projectcast dot com
    22 years ago
    At least with Postgres 7.2, connecting to local postgresdatabase requires a user in the database with the same name as the user running apache, or the connection fails.
    up
    0
    VLroyrenn
    5 years ago
    For what it's worth, it should be noted that, while PHP will generally handle connection-reuse for you so long as you keep using the same connection strings, as in the following example:

    <?php
    $before_conn1     = microtime(true);
    $db1 = pg_connect($conn_string);

    $before_conn2 = microtime(true);
    $db2 = pg_connect($conn_string);
    $after_conn2 = microtime(true);

    echo(    $before_conn2 - $before_conn1); // Takes ~0.03s
    echo("\n");
    echo(    $after_conn2 - $before_conn2); // Takes 0s
    ?>

    ...as nice as it would have been, this does not hold true for async connections; you have to manage those yourself and you can't follow up an async connection with a blocking one later on as an easy way to wait for the connection process to complete before sending queries.

    <?php
    $before_conn1     = microtime(true);
    $db1 = pg_connect($conn_string, PGSQL_CONNECT_ASYNC);
    sleep(1);

    $before_conn2 = microtime(true);
    $db2 = pg_connect($conn_string);
    $after_conn2 = microtime(true);

    echo(    $before_conn2 - $before_conn1); // Takes ~1s
    echo("\n");
    echo(    $after_conn2 - $before_conn2); // Takes ~0.025s
    ?>
    up
    -1
    Anonymous
    19 years ago
    The values accepted by pg_connect's sslmode argument are: disable, allow, prefer, require
    up
    -1
    gutostraube at gmail dot com
    15 years ago
    It's possible connect to a PostgreSQL database via Unix socket using the pg_connect() function by the following two ways:

    1) Using the socket path:

    <?php
    $conn     = pg_connect('host=/var/run/postgresql user=username dbname=databasename');
    ?>

    2) Omitting the host name/path:

    <?php
    $conn     = pg_connect('user=username dbname=databasename');
    ?>

    Note: in this case (omitting the host value), the default socket path will be used.
    up
    -2
    leace at post dot cz
    24 years ago
    If you use PostgreSQL users for authenticating into your pg database rather than using your own authentication, always specify host directive in pg_connect and edit pg_hba.conf to authenticate from this host accordingly. Otherwise, PHP will connect as 'local' using UNIX domain sockets, which is set in pg_hba.conf to 'trust' by default (so you can connect using psql on console without specifying password) and everyone can connect to db _without password_ .
    up
    -2
    phpnet at benjamin dot schulz dot name
    20 years ago
    if you need to open a new connection handle (i.e. for multiple pg_send_query()) use PGSQL_CONNECT_FORCE_NEW as second parameter to pg_connect()
    up
    -2
    floriparob at gmail dot com
    8 years ago
    Using the "service" parameter as the connection string -- we found that the following functions:-

    putenv("PGSERVICEFILE=/path/to/your/service/file/pg_service.conf");
    $connect_string = ("service=testdb");
    try {
    $pgconn_handle = pg_connect($connect_string);
    . . . . . etc.

    Note:-
    1) the environment variable has to point to the path AND file name.
    2) the file has to be readable by Apache.

    See:-

    https://www.postgresql.org/docs/9.6/static/libpq-pgservice.html

    for how to create your pg_service.conf
    up
    -3
    Sohel Taslim
    17 years ago
    I got the same problem but I have to solve that in different way.
    In my postgresql.conf file the following was commented.
    So, I active that under Connection Settings-

    # - Connection Settings –
    tcpip_socket = true
    up
    -2
    xzilla at users dot sourceforge dot net
    20 years ago
    regarding the note from matias at nospam dot projectcast dot com
    on 12-Feb-2002 01:16, you do not need a user in the database with the same name a your web user with ANY version of postgresql. The only time that would be a requirement ifs if you set your postgresql server to only allow IDENT based authentication (which IIRC is the default on Red Hat systems, which might be what lead to the confusion). For more info on the various authentication methods allowed by postgresql, check out http://www.postgresql.org/docs/7.4/static/client-authentication.html
    up
    -2
    jtate at php dot net
    21 years ago
    If you use host=HOSTNAME in your pg_connect string when connecting to PostgreSQL databases newer than 7.1, you need to make sure that your postmaster daemon is started with the "-i" option. Otherwise the connection will fail. See http://www.postgresql.org/idocs/index.php?client-authentication.html for client authentication documentation.
    up
    -3
    kayotix at yahoo dot com
    24 years ago
    Little note that is buried in the install somewhere. In Php 3, PostgreSQL support was activated by adding --with-postgresql=[DIR] to the options passed to ./configure. With Php 4.0.2 (on Linux) the parameter was --with-pgsql. The only place I found this was in the installing PHP on Unix section of the manual.
    up
    -3
    rolf at sir-wum dot de
    23 years ago
    pg_connect() won't work with the authentication method 'crypt' in the pg_hba.conf. Took me an hour to figure that out till I remeberd some other issues with windows missing the crypt() call.
    up
    -5
    derry at siliconriver.com dot au
    21 years ago
    pg_connect seems to support SSL connections, on systems where Postgres has been compiled with ssl, i'm assuming this is since psql uses libpq to connect.
    pg_connect can successfully connect, and use the "requiressl" argument.
    up
    -5
    borovik -at- gmail
    17 years ago
    "If you use pg_connect('host=localhost port=5432 user=my_username password=my_password dbname=my_dbname') and you get the following error:
    "Warning: pg_connect(): Unable to connect to PostgreSQL server: could not connect to server: Connection refused Is the server running on host localhost and accepting TCP/IP connections on port 5432?"
    "
    I solved this error just by setting listen_addresses = '*' in the postgresql.conf file. This error occurs probably despite of a name resolution to localhost, given in the "host" parameter. So you can set the host in the pg_connect() function.
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