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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>33.1. Database Connection Control Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="libpq.html" title="Chapter 33. libpq - C Library" /><link rel="next" href="libpq-status.html" title="33.2. Connection Status Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">33.1. Database Connection Control Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq.html" title="Chapter 33. libpq - C Library">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 33. libpq - C Library">Up</a></td><th width="60%" align="center">Chapter 33. <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> - C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-status.html" title="33.2. Connection Status Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LIBPQ-CONNECT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">33.1. Database Connection Control Functions</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="libpq-connect.html#LIBPQ-CONNSTRING">33.1.1. Connection Strings</a></span></dt><dt><span class="sect2"><a href="libpq-connect.html#LIBPQ-PARAMKEYWORDS">33.1.2. Parameter Key Words</a></span></dt></dl></div><p>

  3.    The following functions deal with making a connection to a

  4.    <span class="productname">PostgreSQL</span> backend server.  An

  5.    application program can have several backend connections open at

  6.    one time.  (One reason to do that is to access more than one

  7.    database.)  Each connection is represented by a

  8.    <code class="structname">PGconn</code><a id="id-1.7.3.8.2.3" class="indexterm"></a> object, which

  9.    is obtained from the function <code class="function">PQconnectdb</code>,

  10.    <code class="function">PQconnectdbParams</code>, or

  11.    <code class="function">PQsetdbLogin</code>.  Note that these functions will always

  12.    return a non-null object pointer, unless perhaps there is too

  13.    little memory even to allocate the <code class="structname">PGconn</code> object.

  14.    The <code class="function">PQstatus</code> function should be called to check

  15.    the return value for a successful connection before queries are sent

  16.    via the connection object.

  17. 

  18.    </p><div class="warning"><h3 class="title">Warning</h3><p>

  19.      If untrusted users have access to a database that has not adopted a

  20.      <a class="link" href="ddl-schemas.html#DDL-SCHEMAS-PATTERNS" title="5.9.6. Usage Patterns">secure schema usage pattern</a>,

  21.      begin each session by removing publicly-writable schemas from

  22.      <code class="varname">search_path</code>.  One can set parameter key

  23.      word <code class="literal">options</code> to

  24.      value <code class="literal">-csearch_path=</code>.  Alternately, one can

  25.      issue <code class="literal">PQexec(<em class="replaceable"><code>conn</code></em>, "SELECT

  26.      pg_catalog.set_config('search_path', '', false)")</code> after

  27.      connecting.  This consideration is not specific

  28.      to <span class="application">libpq</span>; it applies to every interface for

  29.      executing arbitrary SQL commands.

  30.     </p></div><p>

  31. 

  32.    </p><div class="warning"><h3 class="title">Warning</h3><p>

  33.      On Unix, forking a process with open libpq connections can lead to

  34.      unpredictable results because the parent and child processes share

  35.      the same sockets and operating system resources.  For this reason,

  36.      such usage is not recommended, though doing an <code class="function">exec</code> from

  37.      the child process to load a new executable is safe.

  38.     </p></div><p>

  39. 

  40.    </p><div class="note"><h3 class="title">Note</h3><p>

  41.      On Windows, there is a way to improve performance if a single

  42.      database connection is repeatedly started and shutdown.  Internally,

  43.      libpq calls <code class="function">WSAStartup()</code> and <code class="function">WSACleanup()</code> for connection startup

  44.      and shutdown, respectively.  <code class="function">WSAStartup()</code> increments an internal

  45.      Windows library reference count which is decremented by <code class="function">WSACleanup()</code>.

  46.      When the reference count is just one, calling <code class="function">WSACleanup()</code> frees

  47.      all resources and all DLLs are unloaded.  This is an expensive

  48.      operation.  To avoid this, an application can manually call

  49.      <code class="function">WSAStartup()</code> so resources will not be freed when the last database

  50.      connection is closed.

  51.     </p></div><p>

  52. 

  53.    </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQCONNECTDBPARAMS"><span class="term"><code class="function">PQconnectdbParams</code><a id="id-1.7.3.8.2.12.1.1.2" class="indexterm"></a></span></dt><dd><p>

  54.        Makes a new connection to the database server.

  55. 

  56. </p><pre class="synopsis">

  57. PGconn *PQconnectdbParams(const char * const *keywords,

  58.                           const char * const *values,

  59.                           int expand_dbname);

  60. </pre><p>

  61.       </p><p>

  62.        This function opens a new database connection using the parameters taken

  63.        from two <code class="symbol">NULL</code>-terminated arrays. The first,

  64.        <code class="literal">keywords</code>, is defined as an array of strings, each one

  65.        being a key word. The second, <code class="literal">values</code>, gives the value

  66.        for each key word. Unlike <code class="function">PQsetdbLogin</code> below, the parameter

  67.        set can be extended without changing the function signature, so use of

  68.        this function (or its nonblocking analogs <code class="function">PQconnectStartParams</code>

  69.        and <code class="function">PQconnectPoll</code>) is preferred for new application

  70.        programming.

  71.       </p><p>

  72.        The currently recognized parameter key words are listed in

  73.        <a class="xref" href="libpq-connect.html#LIBPQ-PARAMKEYWORDS" title="33.1.2. Parameter Key Words">Section 33.1.2</a>.

  74.       </p><p>

  75.        When <code class="literal">expand_dbname</code> is non-zero, the

  76.        <em class="parameter"><code>dbname</code></em> key word value is allowed to be recognized

  77.        as a connection string. Only the first occurrence of

  78.        <em class="parameter"><code>dbname</code></em> is expanded this way, any subsequent

  79.        <em class="parameter"><code>dbname</code></em> value is processed as plain database name. More

  80.        details on the possible connection string formats appear in

  81.        <a class="xref" href="libpq-connect.html#LIBPQ-CONNSTRING" title="33.1.1. Connection Strings">Section 33.1.1</a>.

  82.       </p><p>

  83.        The passed arrays can be empty to use all default parameters, or can

  84.        contain one or more parameter settings. They should be matched in length.

  85.        Processing will stop at the first <code class="symbol">NULL</code> element

  86.        in the <code class="literal">keywords</code> array.

  87.       </p><p>

  88.        If  any  parameter is <code class="symbol">NULL</code> or an empty string, the corresponding

  89.        environment variable (see <a class="xref" href="libpq-envars.html" title="33.14. Environment Variables">Section 33.14</a>) is checked.

  90.        If the  environment  variable is not set either, then the indicated

  91.        built-in defaults are used.

  92.       </p><p>

  93.        In general key words are processed from the beginning of these arrays in index

  94.        order. The effect of this is that when key words are repeated, the last processed

  95.        value is retained. Therefore, through careful placement of the

  96.        <em class="parameter"><code>dbname</code></em> key word, it is possible to determine what may

  97.        be overridden by a <em class="parameter"><code>conninfo</code></em> string, and what may not.

  98.       </p></dd><dt id="LIBPQ-PQCONNECTDB"><span class="term"><code class="function">PQconnectdb</code><a id="id-1.7.3.8.2.12.2.1.2" class="indexterm"></a></span></dt><dd><p>

  99.        Makes a new connection to the database server.

  100. 

  101. </p><pre class="synopsis">

  102. PGconn *PQconnectdb(const char *conninfo);

  103. </pre><p>

  104.       </p><p>

  105.        This function opens a new database connection using the parameters taken

  106.        from the string <code class="literal">conninfo</code>.

  107.       </p><p>

  108.        The passed string can be empty to use all default parameters, or it can

  109.        contain one or more parameter settings separated by whitespace,

  110.        or it can contain a <acronym class="acronym">URI</acronym>.

  111.        See <a class="xref" href="libpq-connect.html#LIBPQ-CONNSTRING" title="33.1.1. Connection Strings">Section 33.1.1</a> for details.

  112.      </p></dd><dt id="LIBPQ-PQSETDBLOGIN"><span class="term"><code class="function">PQsetdbLogin</code><a id="id-1.7.3.8.2.12.3.1.2" class="indexterm"></a></span></dt><dd><p>

  113.        Makes a new connection to the database server.

  114. </p><pre class="synopsis">

  115. PGconn *PQsetdbLogin(const char *pghost,

  116.                      const char *pgport,

  117.                      const char *pgoptions,

  118.                      const char *pgtty,

  119.                      const char *dbName,

  120.                      const char *login,

  121.                      const char *pwd);

  122. </pre><p>

  123.        </p><p>

  124.         This is the predecessor of <code class="function">PQconnectdb</code> with a fixed

  125.         set of parameters.  It has the same functionality except that the

  126.         missing parameters will always take on default values.  Write <code class="symbol">NULL</code> or an

  127.         empty string for any one of the fixed parameters that is to be defaulted.

  128.       </p><p>

  129.         If the <em class="parameter"><code>dbName</code></em> contains

  130.         an <code class="symbol">=</code> sign or has a valid connection <acronym class="acronym">URI</acronym> prefix, it

  131.         is taken as a <em class="parameter"><code>conninfo</code></em> string in exactly the same way as

  132.         if it had been passed to <code class="function">PQconnectdb</code>, and the remaining

  133.         parameters are then applied as specified for <code class="function">PQconnectdbParams</code>.

  134.       </p></dd><dt id="LIBPQ-PQSETDB"><span class="term"><code class="function">PQsetdb</code><a id="id-1.7.3.8.2.12.4.1.2" class="indexterm"></a></span></dt><dd><p>

  135.    Makes a new connection to the database server.

  136. </p><pre class="synopsis">

  137. PGconn *PQsetdb(char *pghost,

  138.                 char *pgport,

  139.                 char *pgoptions,

  140.                 char *pgtty,

  141.                 char *dbName);

  142. </pre><p>

  143.      </p><p>

  144.       This is a macro that calls <code class="function">PQsetdbLogin</code> with null pointers

  145.       for the <em class="parameter"><code>login</code></em> and <em class="parameter"><code>pwd</code></em> parameters.  It is provided

  146.       for backward compatibility with very old programs.

  147.      </p></dd><dt id="LIBPQ-PQCONNECTSTARTPARAMS"><span class="term"><code class="function">PQconnectStartParams</code><a id="id-1.7.3.8.2.12.5.1.2" class="indexterm"></a><br /></span><span class="term"><code class="function">PQconnectStart</code><a id="id-1.7.3.8.2.12.5.2.2" class="indexterm"></a><br /></span><span class="term"><code class="function">PQconnectPoll</code><a id="id-1.7.3.8.2.12.5.3.2" class="indexterm"></a></span></dt><dd><p>

  148.        <a id="id-1.7.3.8.2.12.5.4.1.1" class="indexterm"></a>

  149.        Make a connection to the database server in a nonblocking manner.

  150. 

  151. </p><pre class="synopsis">

  152. PGconn *PQconnectStartParams(const char * const *keywords,

  153.                              const char * const *values,

  154.                              int expand_dbname);

  155. 

  156. PGconn *PQconnectStart(const char *conninfo);

  157. 

  158. PostgresPollingStatusType PQconnectPoll(PGconn *conn);

  159. </pre><p>

  160.       </p><p>

  161.        These three functions are used to open a connection to a database server such

  162.        that your application's thread of execution is not blocked on remote I/O

  163.        whilst doing so. The point of this approach is that the waits for I/O to

  164.        complete can occur in the application's main loop, rather than down inside

  165.        <code class="function">PQconnectdbParams</code> or <code class="function">PQconnectdb</code>, and so the

  166.        application can manage this operation in parallel with other activities.

  167.       </p><p>

  168.        With <code class="function">PQconnectStartParams</code>, the database connection is made

  169.        using the parameters taken from the <code class="literal">keywords</code> and

  170.        <code class="literal">values</code> arrays, and controlled by <code class="literal">expand_dbname</code>,

  171.        as described above for <code class="function">PQconnectdbParams</code>.

  172.       </p><p>

  173.        With <code class="function">PQconnectStart</code>, the database connection is made

  174.        using the parameters taken from the string <code class="literal">conninfo</code> as

  175.        described above for <code class="function">PQconnectdb</code>.

  176.       </p><p>

  177.        Neither <code class="function">PQconnectStartParams</code> nor <code class="function">PQconnectStart</code>

  178.        nor <code class="function">PQconnectPoll</code> will block, so long as a number of

  179.        restrictions are met:

  180.        </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  181.           The <code class="literal">hostaddr</code> parameter must be used appropriately

  182.           to prevent DNS queries from being made.  See the documentation of

  183.           this parameter in <a class="xref" href="libpq-connect.html#LIBPQ-PARAMKEYWORDS" title="33.1.2. Parameter Key Words">Section 33.1.2</a> for details.

  184.          </p></li><li class="listitem"><p>

  185.           If you call <code class="function">PQtrace</code>, ensure that the stream object

  186.           into which you trace will not block.

  187.          </p></li><li class="listitem"><p>

  188.           You must ensure that the socket is in the appropriate state

  189.           before calling <code class="function">PQconnectPoll</code>, as described below.

  190.          </p></li></ul></div><p>

  191.       </p><p>

  192.        To begin a nonblocking connection request,

  193.        call <code class="function">PQconnectStart</code>

  194.        or <code class="function">PQconnectStartParams</code>.  If the result is null,

  195.        then <span class="application">libpq</span> has been unable to allocate a

  196.        new <code class="structname">PGconn</code> structure.  Otherwise, a

  197.        valid <code class="structname">PGconn</code> pointer is returned (though not

  198.        yet representing a valid connection to the database).  Next

  199.        call <code class="literal">PQstatus(conn)</code>.  If the result

  200.        is <code class="symbol">CONNECTION_BAD</code>, the connection attempt has already

  201.        failed, typically because of invalid connection parameters.

  202.       </p><p>

  203.        If <code class="function">PQconnectStart</code>

  204.        or <code class="function">PQconnectStartParams</code> succeeds, the next stage

  205.        is to poll <span class="application">libpq</span> so that it can proceed with

  206.        the connection sequence.

  207.        Use <code class="function">PQsocket(conn)</code> to obtain the descriptor of the

  208.        socket underlying the database connection.

  209.        (Caution: do not assume that the socket remains the same

  210.        across <code class="function">PQconnectPoll</code> calls.)

  211.        Loop thus: If <code class="function">PQconnectPoll(conn)</code> last returned

  212.        <code class="symbol">PGRES_POLLING_READING</code>, wait until the socket is ready to

  213.        read (as indicated by <code class="function">select()</code>, <code class="function">poll()</code>, or

  214.        similar system function).

  215.        Then call <code class="function">PQconnectPoll(conn)</code> again.

  216.        Conversely, if <code class="function">PQconnectPoll(conn)</code> last returned

  217.        <code class="symbol">PGRES_POLLING_WRITING</code>, wait until the socket is ready

  218.        to write, then call <code class="function">PQconnectPoll(conn)</code> again.

  219.        On the first iteration, i.e. if you have yet to call

  220.        <code class="function">PQconnectPoll</code>, behave as if it last returned

  221.        <code class="symbol">PGRES_POLLING_WRITING</code>.  Continue this loop until

  222.        <code class="function">PQconnectPoll(conn)</code> returns

  223.        <code class="symbol">PGRES_POLLING_FAILED</code>, indicating the connection procedure

  224.        has failed, or <code class="symbol">PGRES_POLLING_OK</code>, indicating the connection

  225.        has been successfully made.

  226.       </p><p>

  227.        At any time during connection, the status of the connection can be

  228.        checked by calling <code class="function">PQstatus</code>. If this call returns <code class="symbol">CONNECTION_BAD</code>, then the

  229.        connection procedure has failed; if the call returns <code class="function">CONNECTION_OK</code>, then the

  230.        connection is ready.  Both of these states are equally detectable

  231.        from the return value of <code class="function">PQconnectPoll</code>, described above. Other states might also occur

  232.        during (and only during) an asynchronous connection procedure. These

  233.        indicate the current stage of the connection procedure and might be useful

  234.        to provide feedback to the user for example. These statuses are:

  235. 

  236.        </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-CONNECTION-STARTED"><span class="term"><code class="symbol">CONNECTION_STARTED</code></span></dt><dd><p>

  237.            Waiting for connection to be made.

  238.           </p></dd><dt id="LIBPQ-CONNECTION-MADE"><span class="term"><code class="symbol">CONNECTION_MADE</code></span></dt><dd><p>

  239.            Connection OK; waiting to send.

  240.           </p></dd><dt id="LIBPQ-CONNECTION-AWAITING-RESPONSE"><span class="term"><code class="symbol">CONNECTION_AWAITING_RESPONSE</code></span></dt><dd><p>

  241.            Waiting for a response from the server.

  242.           </p></dd><dt id="LIBPQ-CONNECTION-AUTH-OK"><span class="term"><code class="symbol">CONNECTION_AUTH_OK</code></span></dt><dd><p>

  243.            Received authentication; waiting for backend start-up to finish.

  244.           </p></dd><dt id="LIBPQ-CONNECTION-SSL-STARTUP"><span class="term"><code class="symbol">CONNECTION_SSL_STARTUP</code></span></dt><dd><p>

  245.            Negotiating SSL encryption.

  246.           </p></dd><dt id="LIBPQ-CONNECTION-SETENV"><span class="term"><code class="symbol">CONNECTION_SETENV</code></span></dt><dd><p>

  247.            Negotiating environment-driven parameter settings.

  248.           </p></dd><dt id="LIBPQ-CONNECTION-CHECK-WRITABLE"><span class="term"><code class="symbol">CONNECTION_CHECK_WRITABLE</code></span></dt><dd><p>

  249.            Checking if connection is able to handle write transactions.

  250.           </p></dd><dt id="LIBPQ-CONNECTION-CONSUME"><span class="term"><code class="symbol">CONNECTION_CONSUME</code></span></dt><dd><p>

  251.            Consuming any remaining response messages on connection.

  252.           </p></dd></dl></div><p>

  253. 

  254.        Note that, although these constants will remain (in order to maintain

  255.        compatibility), an application should never rely upon these occurring in a

  256.        particular order, or at all, or on the status always being one of these

  257.        documented values. An application might do something like this:

  258. </p><pre class="programlisting">

  259. switch(PQstatus(conn))

  260. {

  261.         case CONNECTION_STARTED:

  262.             feedback = "Connecting...";

  263.             break;

  264. 

  265.         case CONNECTION_MADE:

  266.             feedback = "Connected to server...";

  267.             break;

  268. .

  269. .

  270. .

  271.         default:

  272.             feedback = "Connecting...";

  273. }

  274. </pre><p>

  275.       </p><p>

  276.        The <code class="literal">connect_timeout</code> connection parameter is ignored

  277.        when using <code class="function">PQconnectPoll</code>; it is the application's

  278.        responsibility to decide whether an excessive amount of time has elapsed.

  279.        Otherwise, <code class="function">PQconnectStart</code> followed by a

  280.        <code class="function">PQconnectPoll</code> loop is equivalent to

  281.        <code class="function">PQconnectdb</code>.

  282.       </p><p>

  283.        Note that when <code class="function">PQconnectStart</code>

  284.        or <code class="function">PQconnectStartParams</code> returns a non-null

  285.        pointer, you must call <code class="function">PQfinish</code> when you are

  286.        finished with it, in order to dispose of the structure and any

  287.        associated memory blocks.  This must be done even if the connection

  288.        attempt fails or is abandoned.

  289.       </p></dd><dt id="LIBPQ-PQCONNDEFAULTS"><span class="term"><code class="function">PQconndefaults</code><a id="id-1.7.3.8.2.12.6.1.2" class="indexterm"></a></span></dt><dd><p>

  290.        Returns the default connection options.

  291. </p><pre class="synopsis">

  292. PQconninfoOption *PQconndefaults(void);

  293. 

  294. typedef struct

  295. {

  296.     char   *keyword;   /* The keyword of the option */

  297.     char   *envvar;    /* Fallback environment variable name */

  298.     char   *compiled;  /* Fallback compiled in default value */

  299.     char   *val;       /* Option's current value, or NULL */

  300.     char   *label;     /* Label for field in connect dialog */

  301.     char   *dispchar;  /* Indicates how to display this field

  302.                           in a connect dialog. Values are:

  303.                           ""        Display entered value as is

  304.                           "*"       Password field - hide value

  305.                           "D"       Debug option - don't show by default */

  306.     int     dispsize;  /* Field size in characters for dialog */

  307. } PQconninfoOption;

  308. </pre><p>

  309.       </p><p>

  310.        Returns a connection options array.  This can be used to determine

  311.        all possible <code class="function">PQconnectdb</code> options and their

  312.        current default values.  The return value points to an array of

  313.        <code class="structname">PQconninfoOption</code> structures, which ends

  314.        with an entry having a null <code class="structfield">keyword</code> pointer.  The

  315.        null pointer is returned if memory could not be allocated. Note that

  316.        the current default values (<code class="structfield">val</code> fields)

  317.        will depend on environment variables and other context.  A

  318.        missing or invalid service file will be silently ignored.  Callers

  319.        must treat the connection options data as read-only.

  320.       </p><p>

  321.        After processing the options array, free it by passing it to

  322.        <code class="function">PQconninfoFree</code>.  If this is not done, a small amount of memory

  323.        is leaked for each call to <code class="function">PQconndefaults</code>.

  324.       </p></dd><dt id="LIBPQ-PQCONNINFO"><span class="term"><code class="function">PQconninfo</code><a id="id-1.7.3.8.2.12.7.1.2" class="indexterm"></a></span></dt><dd><p>

  325.        Returns the connection options used by a live connection.

  326. </p><pre class="synopsis">

  327. PQconninfoOption *PQconninfo(PGconn *conn);

  328. </pre><p>

  329.       </p><p>

  330.        Returns a connection options array.  This can be used to determine

  331.        all possible <code class="function">PQconnectdb</code> options and the

  332.        values that were used to connect to the server. The return

  333.        value points to an array of <code class="structname">PQconninfoOption</code>

  334.        structures, which ends with an entry having a null <code class="structfield">keyword</code>

  335.        pointer. All notes above for <code class="function">PQconndefaults</code> also

  336.        apply to the result of <code class="function">PQconninfo</code>.

  337.       </p></dd><dt id="LIBPQ-PQCONNINFOPARSE"><span class="term"><code class="function">PQconninfoParse</code><a id="id-1.7.3.8.2.12.8.1.2" class="indexterm"></a></span></dt><dd><p>

  338.        Returns parsed connection options from the provided connection string.

  339. 

  340. </p><pre class="synopsis">

  341. PQconninfoOption *PQconninfoParse(const char *conninfo, char **errmsg);

  342. </pre><p>

  343.       </p><p>

  344.        Parses a connection string and returns the resulting options as an

  345.        array; or returns <code class="symbol">NULL</code> if there is a problem with the connection

  346.        string.  This function can be used to extract

  347.        the <code class="function">PQconnectdb</code> options in the provided

  348.        connection string.  The return value points to an array of

  349.        <code class="structname">PQconninfoOption</code> structures, which ends

  350.        with an entry having a null <code class="structfield">keyword</code> pointer.

  351.       </p><p>

  352.        All legal options will be present in the result array, but the

  353.        <code class="literal">PQconninfoOption</code> for any option not present

  354.        in the connection string will have <code class="literal">val</code> set to

  355.        <code class="literal">NULL</code>; default values are not inserted.

  356.       </p><p>

  357.        If <code class="literal">errmsg</code> is not <code class="symbol">NULL</code>, then <code class="literal">*errmsg</code> is set

  358.        to <code class="symbol">NULL</code> on success, else to a <code class="function">malloc</code>'d error string explaining

  359.        the problem.  (It is also possible for <code class="literal">*errmsg</code> to be

  360.        set to <code class="symbol">NULL</code> and the function to return <code class="symbol">NULL</code>;

  361.        this indicates an out-of-memory condition.)

  362.       </p><p>

  363.        After processing the options array, free it by passing it to

  364.        <code class="function">PQconninfoFree</code>.  If this is not done, some memory

  365.        is leaked for each call to <code class="function">PQconninfoParse</code>.

  366.        Conversely, if an error occurs and <code class="literal">errmsg</code> is not <code class="symbol">NULL</code>,

  367.        be sure to free the error string using <code class="function">PQfreemem</code>.

  368.       </p></dd><dt id="LIBPQ-PQFINISH"><span class="term"><code class="function">PQfinish</code><a id="id-1.7.3.8.2.12.9.1.2" class="indexterm"></a></span></dt><dd><p>

  369.        Closes  the  connection to the server.  Also frees

  370.        memory used by the <code class="structname">PGconn</code> object.

  371. </p><pre class="synopsis">

  372. void PQfinish(PGconn *conn);

  373. </pre><p>

  374.       </p><p>

  375.        Note that even if the server connection attempt fails (as

  376.        indicated by <code class="function">PQstatus</code>), the application should call <code class="function">PQfinish</code>

  377.        to free the memory used by the <code class="structname">PGconn</code> object.

  378.        The <code class="structname">PGconn</code> pointer must not be used again after

  379.        <code class="function">PQfinish</code> has been called.

  380.       </p></dd><dt id="LIBPQ-PQRESET"><span class="term"><code class="function">PQreset</code><a id="id-1.7.3.8.2.12.10.1.2" class="indexterm"></a></span></dt><dd><p>

  381.        Resets the communication channel to the server.

  382. </p><pre class="synopsis">

  383. void PQreset(PGconn *conn);

  384. </pre><p>

  385.       </p><p>

  386.        This function will close the connection

  387.        to the server and attempt to  reestablish  a  new

  388.        connection to the same server, using all the same

  389.        parameters previously used.  This might be useful for

  390.        error recovery if a working connection is lost.

  391.       </p></dd><dt id="LIBPQ-PQRESETSTART"><span class="term"><code class="function">PQresetStart</code><a id="id-1.7.3.8.2.12.11.1.2" class="indexterm"></a><br /></span><span class="term"><code class="function">PQresetPoll</code><a id="id-1.7.3.8.2.12.11.2.2" class="indexterm"></a></span></dt><dd><p>

  392.        Reset the communication channel to the server, in a nonblocking manner.

  393. 

  394. </p><pre class="synopsis">

  395. int PQresetStart(PGconn *conn);

  396. 

  397. PostgresPollingStatusType PQresetPoll(PGconn *conn);

  398. </pre><p>

  399.       </p><p>

  400.        These functions will close the connection to the server and attempt to

  401.        reestablish a new connection to the same server, using all the same

  402.        parameters previously used. This can be useful for error recovery if a

  403.        working connection is lost. They differ from <code class="function">PQreset</code> (above) in that they

  404.        act in a nonblocking manner. These functions suffer from the same

  405.        restrictions as <code class="function">PQconnectStartParams</code>, <code class="function">PQconnectStart</code>

  406.        and <code class="function">PQconnectPoll</code>.

  407.       </p><p>

  408.        To initiate a connection reset, call

  409.        <code class="function">PQresetStart</code>. If it returns 0, the reset has

  410.        failed. If it returns 1, poll the reset using

  411.        <code class="function">PQresetPoll</code> in exactly the same way as you

  412.        would create the connection using <code class="function">PQconnectPoll</code>.

  413.       </p></dd><dt id="LIBPQ-PQPINGPARAMS"><span class="term"><code class="function">PQpingParams</code><a id="id-1.7.3.8.2.12.12.1.2" class="indexterm"></a></span></dt><dd><p>

  414.        <code class="function">PQpingParams</code> reports the status of the

  415.        server.  It accepts connection parameters identical to those of

  416.        <code class="function">PQconnectdbParams</code>, described above.  It is not

  417.        necessary to supply correct user name, password, or database name

  418.        values to obtain the server status; however, if incorrect values

  419.        are provided, the server will log a failed connection attempt.

  420. 

  421. </p><pre class="synopsis">

  422. PGPing PQpingParams(const char * const *keywords,

  423.                     const char * const *values,

  424.                     int expand_dbname);

  425. </pre><p>

  426. 

  427.        The function returns one of the following values:

  428. 

  429.        </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-PQPINGPARAMS-PQPING-OK"><span class="term"><code class="literal">PQPING_OK</code></span></dt><dd><p>

  430.            The server is running and appears to be accepting connections.

  431.           </p></dd><dt id="LIBPQ-PQPINGPARAMS-PQPING-REJECT"><span class="term"><code class="literal">PQPING_REJECT</code></span></dt><dd><p>

  432.            The server is running but is in a state that disallows connections

  433.            (startup, shutdown, or crash recovery).

  434.           </p></dd><dt id="LIBPQ-PQPINGPARAMS-PQPING-NO-RESPONSE"><span class="term"><code class="literal">PQPING_NO_RESPONSE</code></span></dt><dd><p>

  435.            The server could not be contacted.  This might indicate that the

  436.            server is not running, or that there is something wrong with the

  437.            given connection parameters (for example, wrong port number), or

  438.            that there is a network connectivity problem (for example, a

  439.            firewall blocking the connection request).

  440.           </p></dd><dt id="LIBPQ-PQPINGPARAMS-PQPING-NO-ATTEMPT"><span class="term"><code class="literal">PQPING_NO_ATTEMPT</code></span></dt><dd><p>

  441.            No attempt was made to contact the server, because the supplied

  442.            parameters were obviously incorrect or there was some client-side

  443.            problem (for example, out of memory).

  444.           </p></dd></dl></div><p>

  445. 

  446.       </p></dd><dt id="LIBPQ-PQPING"><span class="term"><code class="function">PQping</code><a id="id-1.7.3.8.2.12.13.1.2" class="indexterm"></a></span></dt><dd><p>

  447.        <code class="function">PQping</code> reports the status of the

  448.        server.  It accepts connection parameters identical to those of

  449.        <code class="function">PQconnectdb</code>, described above.  It is not

  450.        necessary to supply correct user name, password, or database name

  451.        values to obtain the server status; however, if incorrect values

  452.        are provided, the server will log a failed connection attempt.

  453. 

  454. </p><pre class="synopsis">

  455. PGPing PQping(const char *conninfo);

  456. </pre><p>

  457.       </p><p>

  458.        The return values are the same as for <code class="function">PQpingParams</code>.

  459.       </p></dd></dl></div><p>

  460.   </p><div class="sect2" id="LIBPQ-CONNSTRING"><div class="titlepage"><div><div><h3 class="title">33.1.1. Connection Strings</h3></div></div></div><a id="id-1.7.3.8.3.2" class="indexterm"></a><a id="id-1.7.3.8.3.3" class="indexterm"></a><p>

  461.     Several <span class="application">libpq</span> functions parse a user-specified string to obtain

  462.     connection parameters.  There are two accepted formats for these strings:

  463.     plain <code class="literal">keyword = value</code> strings

  464.     and URIs.  URIs generally follow

  465.     <a class="ulink" href="https://tools.ietf.org/html/rfc3986" target="_top">RFC

  466.     3986</a>, except that multi-host connection strings are allowed

  467.     as further described below.

  468.    </p><div class="sect3" id="id-1.7.3.8.3.5"><div class="titlepage"><div><div><h4 class="title">33.1.1.1. Keyword/Value Connection Strings</h4></div></div></div><p>

  469.     In the first format, each parameter setting is in the form

  470.     <code class="literal">keyword = value</code>.  Spaces around the equal sign are

  471.     optional. To write an empty value, or a value containing spaces, surround it

  472.     with single quotes, e.g., <code class="literal">keyword = 'a value'</code>. Single

  473.     quotes and backslashes within

  474.     the value must be escaped with a backslash, i.e., <code class="literal">\'</code> and

  475.     <code class="literal">\\</code>.

  476.    </p><p>

  477.     Example:

  478. </p><pre class="programlisting">

  479. host=localhost port=5432 dbname=mydb connect_timeout=10

  480. </pre><p>

  481.    </p><p>

  482.     The recognized parameter key words are listed in <a class="xref" href="libpq-connect.html#LIBPQ-PARAMKEYWORDS" title="33.1.2. Parameter Key Words">Section 33.1.2</a>.

  483.    </p></div><div class="sect3" id="id-1.7.3.8.3.6"><div class="titlepage"><div><div><h4 class="title">33.1.1.2. Connection URIs</h4></div></div></div><p>

  484.    The general form for a connection <acronym class="acronym">URI</acronym> is:

  485. </p><pre class="synopsis">

  486. postgresql://[user[:password]@][netloc][:port][,...][/dbname][?param1=value1&amp;...]

  487. </pre><p>

  488.    </p><p>

  489.     The <acronym class="acronym">URI</acronym> scheme designator can be either

  490.     <code class="literal">postgresql://</code> or <code class="literal">postgres://</code>.  Each

  491.     of the <acronym class="acronym">URI</acronym> parts is optional.  The following examples

  492.     illustrate valid <acronym class="acronym">URI</acronym> syntax uses:

  493. </p><pre class="programlisting">

  494. postgresql://

  495. postgresql://localhost

  496. postgresql://localhost:5433

  497. postgresql://localhost/mydb

  498. postgresql://user@localhost

  499. postgresql://user:secret@localhost

  500. postgresql://other@localhost/otherdb?connect_timeout=10&amp;application_name=myapp

  501. postgresql://host1:123,host2:456/somedb?target_session_attrs=any&amp;application_name=myapp

  502. </pre><p>

  503.     Components of the hierarchical part of the <acronym class="acronym">URI</acronym> can also

  504.     be given as parameters.  For example:

  505. </p><pre class="programlisting">

  506. postgresql:///mydb?host=localhost&amp;port=5433

  507. </pre><p>

  508.    </p><p>

  509.     Percent-encoding may be used to include symbols with special meaning in any

  510.     of the <acronym class="acronym">URI</acronym> parts, e.g. replace <code class="literal">=</code> with

  511.     <code class="literal">%3D</code>.

  512. 

  513.    </p><p>

  514.     Any connection parameters not corresponding to key words listed in <a class="xref" href="libpq-connect.html#LIBPQ-PARAMKEYWORDS" title="33.1.2. Parameter Key Words">Section 33.1.2</a> are ignored and a warning message about them

  515.     is sent to <code class="filename">stderr</code>.

  516.    </p><p>

  517.     For improved compatibility with JDBC connection <acronym class="acronym">URI</acronym>s,

  518.     instances of parameter <code class="literal">ssl=true</code> are translated into

  519.     <code class="literal">sslmode=require</code>.

  520.    </p><p>

  521.     The host part may be either host name or an IP address.  To specify an

  522.     IPv6 host address, enclose it in square brackets:

  523. </p><pre class="synopsis">

  524. postgresql://[2001:db8::1234]/database

  525. </pre><p>

  526.    </p><p>

  527.     The host component is interpreted as described for the parameter <a class="xref" href="libpq-connect.html#LIBPQ-CONNECT-HOST">host</a>.  In particular, a Unix-domain socket

  528.     connection is chosen if the host part is either empty or starts with a

  529.     slash, otherwise a TCP/IP connection is initiated.  Note, however, that the

  530.     slash is a reserved character in the hierarchical part of the URI.  So, to

  531.     specify a non-standard Unix-domain socket directory, either omit the host

  532.     specification in the URI and specify the host as a parameter, or

  533.     percent-encode the path in the host component of the URI:

  534. </p><pre class="programlisting">

  535. postgresql:///dbname?host=/var/lib/postgresql

  536. postgresql://%2Fvar%2Flib%2Fpostgresql/dbname

  537. </pre><p>

  538.    </p><p>

  539.     It is possible to specify multiple host components, each with an optional

  540.     port component, in a single URI.  A URI of the form

  541.     <code class="literal">postgresql://host1:port1,host2:port2,host3:port3/</code>

  542.     is equivalent to a connection string of the form

  543.     <code class="literal">host=host1,host2,host3 port=port1,port2,port3</code>.  Each

  544.     host will be tried in turn until a connection is successfully established.

  545.    </p></div><div class="sect3" id="LIBPQ-MULTIPLE-HOSTS"><div class="titlepage"><div><div><h4 class="title">33.1.1.3. Specifying Multiple Hosts</h4></div></div></div><p>

  546.        It is possible to specify multiple hosts to connect to, so that they are

  547.        tried in the given order. In the Keyword/Value format, the <code class="literal">host</code>,

  548.        <code class="literal">hostaddr</code>, and <code class="literal">port</code> options accept a comma-separated

  549.        list of values. The same number of elements must be given in each

  550.        option that is specified, such

  551.        that e.g. the first <code class="literal">hostaddr</code> corresponds to the first host name,

  552.        the second <code class="literal">hostaddr</code> corresponds to the second host name, and so

  553.        forth. As an exception, if only one <code class="literal">port</code> is specified, it

  554.        applies to all the hosts.

  555.      </p><p>

  556.        In the connection URI format, you can list multiple <code class="literal">host:port</code> pairs

  557.        separated by commas, in the <code class="literal">host</code> component of the URI.

  558.      </p><p>

  559.        In either format, a single host name can translate to multiple network

  560.        addresses. A common example of this is a host that has both an IPv4 and

  561.        an IPv6 address.

  562.      </p><p>

  563.        When multiple hosts are specified, or when a single host name is

  564.        translated to multiple addresses,  all the hosts and addresses will be

  565.        tried in order, until one succeeds. If none of the hosts can be reached,

  566.        the connection fails. If a connection is established successfully, but

  567.        authentication fails, the remaining hosts in the list are not tried.

  568.      </p><p>

  569.        If a password file is used, you can have different passwords for

  570.        different hosts. All the other connection options are the same for every

  571.        host in the list; it is not possible to e.g. specify different

  572.        usernames for different hosts.

  573.      </p></div></div><div class="sect2" id="LIBPQ-PARAMKEYWORDS"><div class="titlepage"><div><div><h3 class="title">33.1.2. Parameter Key Words</h3></div></div></div><p>

  574.     The currently recognized parameter key words are:

  575. 

  576.     </p><div class="variablelist"><dl class="variablelist"><dt id="LIBPQ-CONNECT-HOST"><span class="term"><code class="literal">host</code></span></dt><dd><p>

  577.         Name of host to connect to.<a id="id-1.7.3.8.4.2.1.1.2.1.1" class="indexterm"></a>

  578.         If a host name begins with a slash, it specifies Unix-domain

  579.         communication rather than TCP/IP communication; the value is the

  580.         name of the directory in which the socket file is stored.

  581.         The default behavior when <code class="literal">host</code> is

  582.         not specified, or is empty, is to connect to a Unix-domain

  583.         socket<a id="id-1.7.3.8.4.2.1.1.2.1.3" class="indexterm"></a> in

  584.         <code class="filename">/tmp</code> (or whatever socket directory was specified

  585.         when <span class="productname">PostgreSQL</span> was built). On machines without

  586.         Unix-domain sockets, the default is to connect to <code class="literal">localhost</code>.

  587.        </p><p>

  588.         A comma-separated list of host names is also accepted, in which case

  589.         each host name in the list is tried in order; an empty item in the

  590.         list selects the default behavior as explained above. See

  591.         <a class="xref" href="libpq-connect.html#LIBPQ-MULTIPLE-HOSTS" title="33.1.1.3. Specifying Multiple Hosts">Section 33.1.1.3</a> for details.

  592.        </p></dd><dt id="LIBPQ-CONNECT-HOSTADDR"><span class="term"><code class="literal">hostaddr</code></span></dt><dd><p>

  593.         Numeric IP address of host to connect to.  This should be in the

  594.         standard IPv4 address format, e.g., <code class="literal">172.28.40.9</code>.  If

  595.         your machine supports IPv6, you can also use those addresses.

  596.         TCP/IP communication is

  597.         always used when a nonempty string is specified for this parameter.

  598.        </p><p>

  599.         Using <code class="literal">hostaddr</code> instead of <code class="literal">host</code> allows the

  600.         application to avoid a host name look-up, which might be important

  601.         in applications with time constraints. However, a host name is

  602.         required for GSSAPI or SSPI authentication

  603.         methods, as well as for <code class="literal">verify-full</code> SSL

  604.         certificate verification.  The following rules are used:

  605.         </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  606.            If <code class="literal">host</code> is specified

  607.            without <code class="literal">hostaddr</code>, a host name lookup occurs.

  608.            (When using <code class="function">PQconnectPoll</code>, the lookup occurs

  609.            when <code class="function">PQconnectPoll</code> first considers this host

  610.            name, and it may cause <code class="function">PQconnectPoll</code> to block

  611.            for a significant amount of time.)

  612.           </p></li><li class="listitem"><p>

  613.            If <code class="literal">hostaddr</code> is specified without <code class="literal">host</code>,

  614.            the value for <code class="literal">hostaddr</code> gives the server network address.

  615.            The connection attempt will fail if the authentication

  616.            method requires a host name.

  617.           </p></li><li class="listitem"><p>

  618.            If both <code class="literal">host</code> and <code class="literal">hostaddr</code> are specified,

  619.            the value for <code class="literal">hostaddr</code> gives the server network address.

  620.            The value for <code class="literal">host</code> is ignored unless the

  621.            authentication method requires it, in which case it will be

  622.            used as the host name.

  623.           </p></li></ul></div><p>

  624.         Note that authentication is likely to fail if <code class="literal">host</code>

  625.         is not the name of the server at network address <code class="literal">hostaddr</code>.

  626.         Also, when both <code class="literal">host</code> and <code class="literal">hostaddr</code>

  627.         are specified, <code class="literal">host</code>

  628.         is used to identify the connection in a password file (see

  629.         <a class="xref" href="libpq-pgpass.html" title="33.15. The Password File">Section 33.15</a>).

  630.        </p><p>

  631.         A comma-separated list of <code class="literal">hostaddr</code> values is also

  632.         accepted, in which case each host in the list is tried in order.

  633.         An empty item in the list causes the corresponding host name to be

  634.         used, or the default host name if that is empty as well. See

  635.         <a class="xref" href="libpq-connect.html#LIBPQ-MULTIPLE-HOSTS" title="33.1.1.3. Specifying Multiple Hosts">Section 33.1.1.3</a> for details.

  636.        </p><p>

  637.         Without either a host name or host address,

  638.         <span class="application">libpq</span> will connect using a

  639.         local Unix-domain socket; or on machines without Unix-domain

  640.         sockets, it will attempt to connect to <code class="literal">localhost</code>.

  641.        </p></dd><dt id="LIBPQ-CONNECT-PORT"><span class="term"><code class="literal">port</code></span></dt><dd><p>

  642.         Port number to connect to at the server host, or socket file

  643.         name extension for Unix-domain

  644.         connections.<a id="id-1.7.3.8.4.2.1.3.2.1.1" class="indexterm"></a>

  645.         If multiple hosts were given in the <code class="literal">host</code> or

  646.         <code class="literal">hostaddr</code> parameters, this parameter may specify a

  647.         comma-separated list of ports of the same length as the host list, or

  648.         it may specify a single port number to be used for all hosts.

  649.         An empty string, or an empty item in a comma-separated list,

  650.         specifies the default port number established

  651.         when <span class="productname">PostgreSQL</span> was built.

  652.        </p></dd><dt id="LIBPQ-CONNECT-DBNAME"><span class="term"><code class="literal">dbname</code></span></dt><dd><p>

  653.        The database name.  Defaults to be the same as the user name.

  654.        In certain contexts, the value is checked for extended

  655.        formats; see <a class="xref" href="libpq-connect.html#LIBPQ-CONNSTRING" title="33.1.1. Connection Strings">Section 33.1.1</a> for more details on

  656.        those.

  657.       </p></dd><dt id="LIBPQ-CONNECT-USER"><span class="term"><code class="literal">user</code></span></dt><dd><p>

  658.        <span class="productname">PostgreSQL</span> user name to connect as.

  659.        Defaults to be the same as the operating system name of the user

  660.        running the application.

  661.       </p></dd><dt id="LIBPQ-CONNECT-PASSWORD"><span class="term"><code class="literal">password</code></span></dt><dd><p>

  662.        Password to be used if the server demands password authentication.

  663.       </p></dd><dt id="LIBPQ-CONNECT-PASSFILE"><span class="term"><code class="literal">passfile</code></span></dt><dd><p>

  664.        Specifies the name of the file used to store passwords

  665.        (see <a class="xref" href="libpq-pgpass.html" title="33.15. The Password File">Section 33.15</a>).

  666.        Defaults to <code class="filename">~/.pgpass</code>, or

  667.        <code class="filename">%APPDATA%\postgresql\pgpass.conf</code> on Microsoft Windows.

  668.        (No error is reported if this file does not exist.)

  669.       </p></dd><dt id="LIBPQ-CONNECT-CONNECT-TIMEOUT"><span class="term"><code class="literal">connect_timeout</code></span></dt><dd><p>

  670.        Maximum wait for connection, in seconds (write as a decimal integer,

  671.        e.g. <code class="literal">10</code>).  Zero, negative, or not specified means

  672.        wait indefinitely.  The minimum allowed timeout is 2 seconds, therefore

  673.        a value of <code class="literal">1</code> is interpreted as <code class="literal">2</code>.

  674.        This timeout applies separately to each host name or IP address.

  675.        For example, if you specify two hosts and <code class="literal">connect_timeout</code>

  676.        is 5, each host will time out if no connection is made within 5

  677.        seconds, so the total time spent waiting for a connection might be

  678.        up to 10 seconds.

  679.       </p></dd><dt id="LIBPQ-CONNECT-CLIENT-ENCODING"><span class="term"><code class="literal">client_encoding</code></span></dt><dd><p>

  680.        This sets the <code class="varname">client_encoding</code>

  681.        configuration parameter for this connection.  In addition to

  682.        the values accepted by the corresponding server option, you

  683.        can use <code class="literal">auto</code> to determine the right

  684.        encoding from the current locale in the client

  685.        (<code class="envar">LC_CTYPE</code> environment variable on Unix

  686.        systems).

  687.       </p></dd><dt id="LIBPQ-CONNECT-OPTIONS"><span class="term"><code class="literal">options</code></span></dt><dd><p>

  688.         Specifies command-line options to send to the server at connection

  689.         start.  For example, setting this to <code class="literal">-c geqo=off</code> sets the

  690.         session's value of the <code class="varname">geqo</code> parameter to

  691.         <code class="literal">off</code>.  Spaces within this string are considered to

  692.         separate command-line arguments, unless escaped with a backslash

  693.         (<code class="literal">\</code>); write <code class="literal">\\</code> to represent a literal

  694.         backslash.  For a detailed discussion of the available

  695.         options, consult <a class="xref" href="runtime-config.html" title="Chapter 19. Server Configuration">Chapter 19</a>.

  696.        </p></dd><dt id="LIBPQ-CONNECT-APPLICATION-NAME"><span class="term"><code class="literal">application_name</code></span></dt><dd><p>

  697.         Specifies a value for the <a class="xref" href="runtime-config-logging.html#GUC-APPLICATION-NAME">application_name</a>

  698.         configuration parameter.

  699.        </p></dd><dt id="LIBPQ-CONNECT-FALLBACK-APPLICATION-NAME"><span class="term"><code class="literal">fallback_application_name</code></span></dt><dd><p>

  700.         Specifies a fallback value for the <a class="xref" href="runtime-config-logging.html#GUC-APPLICATION-NAME">application_name</a> configuration parameter.

  701.         This value will be used if no value has been given for

  702.         <code class="literal">application_name</code> via a connection parameter or the

  703.         <code class="envar">PGAPPNAME</code> environment variable.  Specifying

  704.         a fallback name is useful in generic utility programs that

  705.         wish to set a default application name but allow it to be

  706.         overridden by the user.

  707.        </p></dd><dt id="LIBPQ-KEEPALIVES"><span class="term"><code class="literal">keepalives</code></span></dt><dd><p>

  708.         Controls whether client-side TCP keepalives are used. The default

  709.         value is 1, meaning on, but you can change this to 0, meaning off,

  710.         if keepalives are not wanted.  This parameter is ignored for

  711.         connections made via a Unix-domain socket.

  712.        </p></dd><dt id="LIBPQ-KEEPALIVES-IDLE"><span class="term"><code class="literal">keepalives_idle</code></span></dt><dd><p>

  713.         Controls the number of seconds of inactivity after which TCP should

  714.         send a keepalive message to the server.  A value of zero uses the

  715.         system default. This parameter is ignored for connections made via a

  716.         Unix-domain socket, or if keepalives are disabled.

  717.         It is only supported on systems where <code class="symbol">TCP_KEEPIDLE</code> or

  718.         an equivalent socket option is available, and on Windows; on other

  719.         systems, it has no effect.

  720.        </p></dd><dt id="LIBPQ-KEEPALIVES-INTERVAL"><span class="term"><code class="literal">keepalives_interval</code></span></dt><dd><p>

  721.         Controls the number of seconds after which a TCP keepalive message

  722.         that is not acknowledged by the server should be retransmitted.  A

  723.         value of zero uses the system default. This parameter is ignored for

  724.         connections made via a Unix-domain socket, or if keepalives are disabled.

  725.         It is only supported on systems where <code class="symbol">TCP_KEEPINTVL</code> or

  726.         an equivalent socket option is available, and on Windows; on other

  727.         systems, it has no effect.

  728.        </p></dd><dt id="LIBPQ-KEEPALIVES-COUNT"><span class="term"><code class="literal">keepalives_count</code></span></dt><dd><p>

  729.         Controls the number of TCP keepalives that can be lost before the

  730.         client's connection to the server is considered dead.  A value of

  731.         zero uses the system default. This parameter is ignored for

  732.         connections made via a Unix-domain socket, or if keepalives are disabled.

  733.         It is only supported on systems where <code class="symbol">TCP_KEEPCNT</code> or

  734.         an equivalent socket option is available; on other systems, it has no

  735.         effect.

  736.        </p></dd><dt id="LIBPQ-TCP-USER-TIMEOUT"><span class="term"><code class="literal">tcp_user_timeout</code></span></dt><dd><p>

  737.         Controls the number of milliseconds that transmitted data may

  738.         remain unacknowledged before a connection is forcibly closed.

  739.         A value of zero uses the system default. This parameter is

  740.         ignored for connections made via a Unix-domain socket.

  741.         It is only supported on systems where <code class="symbol">TCP_USER_TIMEOUT</code>

  742.         is available; on other systems, it has no effect.

  743.        </p></dd><dt id="LIBPQ-CONNECT-TTY"><span class="term"><code class="literal">tty</code></span></dt><dd><p>

  744.        Ignored (formerly, this specified where to send server debug output).

  745.       </p></dd><dt id="LIBPQ-CONNECT-REPLICATION"><span class="term"><code class="literal">replication</code></span></dt><dd><p>

  746.        This option determines whether the connection should use the

  747.        replication protocol instead of the normal protocol.  This is what

  748.        PostgreSQL replication connections as well as tools such as

  749.        <span class="application">pg_basebackup</span> use internally, but it can

  750.        also be used by third-party applications.  For a description of the

  751.        replication protocol, consult <a class="xref" href="protocol-replication.html" title="52.4. Streaming Replication Protocol">Section 52.4</a>.

  752.       </p><p>

  753.        The following values, which are case-insensitive, are supported:

  754.        </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  755.           <code class="literal">true</code>, <code class="literal">on</code>,

  756.           <code class="literal">yes</code>, <code class="literal">1</code>

  757.          </span></dt><dd><p>

  758.            The connection goes into physical replication mode.

  759.           </p></dd><dt><span class="term"><code class="literal">database</code></span></dt><dd><p>

  760.            The connection goes into logical replication mode, connecting to

  761.            the database specified in the <code class="literal">dbname</code> parameter.

  762.           </p></dd><dt><span class="term">

  763.           <code class="literal">false</code>, <code class="literal">off</code>,

  764.           <code class="literal">no</code>, <code class="literal">0</code>

  765.          </span></dt><dd><p>

  766.            The connection is a regular one, which is the default behavior.

  767.           </p></dd></dl></div><p>

  768.       </p><p>

  769.        In physical or logical replication mode, only the simple query protocol

  770.        can be used.

  771.       </p></dd><dt id="LIBPQ-CONNECT-GSSENCMODE"><span class="term"><code class="literal">gssencmode</code></span></dt><dd><p>

  772.         This option determines whether or with what priority a secure

  773.         <acronym class="acronym">GSS</acronym> TCP/IP connection will be negotiated with the

  774.         server. There are three modes:

  775. 

  776.         </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">disable</code></span></dt><dd><p>

  777.             only try a non-<acronym class="acronym">GSSAPI</acronym>-encrypted connection

  778.            </p></dd><dt><span class="term"><code class="literal">prefer</code> (default)</span></dt><dd><p>

  779.             if there are <acronym class="acronym">GSSAPI</acronym> credentials present (i.e.,

  780.             in a credentials cache), first try

  781.             a <acronym class="acronym">GSSAPI</acronym>-encrypted connection; if that fails or

  782.             there are no credentials, try a

  783.             non-<acronym class="acronym">GSSAPI</acronym>-encrypted connection.  This is the

  784.             default when <span class="productname">PostgreSQL</span> has been

  785.             compiled with <acronym class="acronym">GSSAPI</acronym> support.

  786.            </p></dd><dt><span class="term"><code class="literal">require</code></span></dt><dd><p>

  787.             only try a <acronym class="acronym">GSSAPI</acronym>-encrypted connection

  788.            </p></dd></dl></div><p>

  789.        </p><p>

  790.         <code class="literal">gssencmode</code> is ignored for Unix domain socket

  791.         communication.  If <span class="productname">PostgreSQL</span> is compiled

  792.         without GSSAPI support, using the <code class="literal">require</code> option

  793.         will cause an error, while <code class="literal">prefer</code> will be accepted

  794.         but <span class="application">libpq</span> will not actually attempt

  795.         a <acronym class="acronym">GSSAPI</acronym>-encrypted

  796.         connection.<a id="id-1.7.3.8.4.2.1.20.2.2.7" class="indexterm"></a>

  797.        </p></dd><dt id="LIBPQ-CONNECT-SSLMODE"><span class="term"><code class="literal">sslmode</code></span></dt><dd><p>

  798.         This option determines whether or with what priority a secure

  799.         <acronym class="acronym">SSL</acronym> TCP/IP connection will be negotiated with the

  800.         server. There are six modes:

  801. 

  802.         </p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">disable</code></span></dt><dd><p>

  803.             only try a non-<acronym class="acronym">SSL</acronym> connection

  804.            </p></dd><dt><span class="term"><code class="literal">allow</code></span></dt><dd><p>

  805.             first try a non-<acronym class="acronym">SSL</acronym> connection; if that

  806.             fails, try an <acronym class="acronym">SSL</acronym> connection

  807.            </p></dd><dt><span class="term"><code class="literal">prefer</code> (default)</span></dt><dd><p>

  808.             first try an <acronym class="acronym">SSL</acronym> connection; if that fails,

  809.             try a non-<acronym class="acronym">SSL</acronym> connection

  810.            </p></dd><dt><span class="term"><code class="literal">require</code></span></dt><dd><p>

  811.             only try an <acronym class="acronym">SSL</acronym> connection. If a root CA

  812.             file is present, verify the certificate in the same way as

  813.             if <code class="literal">verify-ca</code> was specified

  814.            </p></dd><dt><span class="term"><code class="literal">verify-ca</code></span></dt><dd><p>

  815.             only try an <acronym class="acronym">SSL</acronym> connection, and verify that

  816.             the server certificate is issued by a trusted

  817.             certificate authority (<acronym class="acronym">CA</acronym>)

  818.            </p></dd><dt><span class="term"><code class="literal">verify-full</code></span></dt><dd><p>

  819.             only try an <acronym class="acronym">SSL</acronym> connection, verify that the

  820.             server certificate is issued by a

  821.             trusted <acronym class="acronym">CA</acronym> and that the requested server host name

  822.             matches that in the certificate

  823.            </p></dd></dl></div><p>

  824. 

  825.         See <a class="xref" href="libpq-ssl.html" title="33.18. SSL Support">Section 33.18</a> for a detailed description of how

  826.         these options work.

  827.        </p><p>

  828.         <code class="literal">sslmode</code> is ignored for Unix domain socket

  829.         communication.

  830.         If <span class="productname">PostgreSQL</span> is compiled without SSL support,

  831.         using options <code class="literal">require</code>, <code class="literal">verify-ca</code>, or

  832.         <code class="literal">verify-full</code> will cause an error, while

  833.         options <code class="literal">allow</code> and <code class="literal">prefer</code> will be

  834.         accepted but <span class="application">libpq</span> will not actually attempt

  835.         an <acronym class="acronym">SSL</acronym>

  836.         connection.<a id="id-1.7.3.8.4.2.1.21.2.2.10" class="indexterm"></a>

  837.        </p></dd><dt id="LIBPQ-CONNECT-REQUIRESSL"><span class="term"><code class="literal">requiressl</code></span></dt><dd><p>

  838.         This option is deprecated in favor of the <code class="literal">sslmode</code>

  839.         setting.

  840.        </p><p>

  841.         If set to 1, an <acronym class="acronym">SSL</acronym> connection to the server

  842.         is required (this is equivalent to <code class="literal">sslmode</code>

  843.         <code class="literal">require</code>).  <span class="application">libpq</span> will then refuse

  844.         to connect if the server does not accept an

  845.         <acronym class="acronym">SSL</acronym> connection.  If set to 0 (default),

  846.         <span class="application">libpq</span> will negotiate the connection type with

  847.         the server (equivalent to <code class="literal">sslmode</code>

  848.         <code class="literal">prefer</code>).  This option is only available if

  849.         <span class="productname">PostgreSQL</span> is compiled with SSL support.

  850.        </p></dd><dt id="LIBPQ-CONNECT-SSLCOMPRESSION"><span class="term"><code class="literal">sslcompression</code></span></dt><dd><p>

  851.         If set to 1, data sent over SSL connections will be compressed.  If

  852.         set to 0, compression will be disabled.  The default is 0.  This

  853.         parameter is ignored if a connection without SSL is made.

  854.        </p><p>

  855.         SSL compression is nowadays considered insecure and its use is no

  856.         longer recommended.  <span class="productname">OpenSSL</span> 1.1.0 disables

  857.         compression by default, and many operating system distributions

  858.         disable it in prior versions as well, so setting this parameter to on

  859.         will not have any effect if the server does not accept compression.

  860.         On the other hand, <span class="productname">OpenSSL</span> before 1.0.0

  861.         does not support disabling compression, so this parameter is ignored

  862.         with those versions, and whether compression is used depends on the

  863.         server.

  864.        </p><p>

  865.         If security is not a primary concern, compression can improve

  866.         throughput if the network is the bottleneck.  Disabling compression

  867.         can improve response time and throughput if CPU performance is the

  868.         limiting factor.

  869.        </p></dd><dt id="LIBPQ-CONNECT-SSLCERT"><span class="term"><code class="literal">sslcert</code></span></dt><dd><p>

  870.         This parameter specifies the file name of the client SSL

  871.         certificate, replacing the default

  872.         <code class="filename">~/.postgresql/postgresql.crt</code>.

  873.         This parameter is ignored if an SSL connection is not made.

  874.        </p></dd><dt id="LIBPQ-CONNECT-SSLKEY"><span class="term"><code class="literal">sslkey</code></span></dt><dd><p>

  875.         This parameter specifies the location for the secret key used for

  876.         the client certificate. It can either specify a file name that will

  877.         be used instead of the default

  878.         <code class="filename">~/.postgresql/postgresql.key</code>, or it can specify a key

  879.         obtained from an external <span class="quote">“<span class="quote">engine</span>”</span> (engines are

  880.         <span class="productname">OpenSSL</span> loadable modules).  An external engine

  881.         specification should consist of a colon-separated engine name and

  882.         an engine-specific key identifier.  This parameter is ignored if an

  883.         SSL connection is not made.

  884.        </p></dd><dt id="LIBPQ-CONNECT-SSLROOTCERT"><span class="term"><code class="literal">sslrootcert</code></span></dt><dd><p>

  885.         This parameter specifies the name of a file containing SSL

  886.         certificate authority (<acronym class="acronym">CA</acronym>) certificate(s).

  887.         If the file exists, the server's certificate will be verified

  888.         to be signed by one of these authorities.  The default is

  889.         <code class="filename">~/.postgresql/root.crt</code>.

  890.        </p></dd><dt id="LIBPQ-CONNECT-SSLCRL"><span class="term"><code class="literal">sslcrl</code></span></dt><dd><p>

  891.         This parameter specifies the file name of the SSL certificate

  892.         revocation list (CRL).  Certificates listed in this file, if it

  893.         exists, will be rejected while attempting to authenticate the

  894.         server's certificate.  The default is

  895.         <code class="filename">~/.postgresql/root.crl</code>.

  896.        </p></dd><dt id="LIBPQ-CONNECT-REQUIREPEER"><span class="term"><code class="literal">requirepeer</code></span></dt><dd><p>

  897.         This parameter specifies the operating-system user name of the

  898.         server, for example <code class="literal">requirepeer=postgres</code>.

  899.         When making a Unix-domain socket connection, if this

  900.         parameter is set, the client checks at the beginning of the

  901.         connection that the server process is running under the specified

  902.         user name; if it is not, the connection is aborted with an error.

  903.         This parameter can be used to provide server authentication similar

  904.         to that available with SSL certificates on TCP/IP connections.

  905.         (Note that if the Unix-domain socket is in

  906.         <code class="filename">/tmp</code> or another publicly writable location,

  907.         any user could start a server listening there.  Use this parameter

  908.         to ensure that you are connected to a server run by a trusted user.)

  909.         This option is only supported on platforms for which the

  910.         <code class="literal">peer</code> authentication method is implemented; see

  911.         <a class="xref" href="auth-peer.html" title="20.9. Peer Authentication">Section 20.9</a>.

  912.        </p></dd><dt id="LIBPQ-CONNECT-KRBSRVNAME"><span class="term"><code class="literal">krbsrvname</code></span></dt><dd><p>

  913.         Kerberos service name to use when authenticating with GSSAPI.

  914.         This must match the service name specified in the server

  915.         configuration for Kerberos authentication to succeed. (See also

  916.         <a class="xref" href="gssapi-auth.html" title="20.6. GSSAPI Authentication">Section 20.6</a>.)

  917.        </p></dd><dt id="LIBPQ-CONNECT-GSSLIB"><span class="term"><code class="literal">gsslib</code></span></dt><dd><p>

  918.         GSS library to use for GSSAPI authentication.

  919.         Currently this is disregarded except on Windows builds that include

  920.         both GSSAPI and SSPI support.  In that case, set

  921.         this to <code class="literal">gssapi</code> to cause libpq to use the GSSAPI

  922.         library for authentication instead of the default SSPI.

  923.        </p></dd><dt id="LIBPQ-CONNECT-SERVICE"><span class="term"><code class="literal">service</code></span></dt><dd><p>

  924.         Service name to use for additional parameters.  It specifies a service

  925.         name in <code class="filename">pg_service.conf</code> that holds additional connection parameters.

  926.         This allows applications to specify only a service name so connection parameters

  927.         can be centrally maintained. See <a class="xref" href="libpq-pgservice.html" title="33.16. The Connection Service File">Section 33.16</a>.

  928.        </p></dd><dt id="LIBPQ-CONNECT-TARGET-SESSION-ATTRS"><span class="term"><code class="literal">target_session_attrs</code></span></dt><dd><p>

  929.         If this parameter is set to <code class="literal">read-write</code>, only a

  930.         connection in which read-write transactions are accepted by default

  931.         is considered acceptable.  The query

  932.         <code class="literal">SHOW transaction_read_only</code> will be sent upon any

  933.         successful connection; if it returns <code class="literal">on</code>, the connection

  934.         will be closed.  If multiple hosts were specified in the connection

  935.         string, any remaining servers will be tried just as if the connection

  936.         attempt had failed.  The default value of this parameter,

  937.         <code class="literal">any</code>, regards all connections as acceptable.

  938.       </p></dd></dl></div><p>

  939.    </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="libpq-status.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 33. <span class="application">libpq</span> - C Library </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 33.2. Connection Status Functions</td></tr></table></div></body></html>
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