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postgresql8.2-docs-8.2.14-1mdv2010.0.i586.rpm

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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-CONNECT"
>29.1. Database Connection Control Functions</A
></H1
><P
>   The following functions deal with making a connection to a
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 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
   <TT
CLASS="STRUCTNAME"
>PGconn</TT
><A
NAME="AEN26484"
></A
> object, which
   is obtained from the function <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> or
   <CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
>.  Note that these functions will always
   return a non-null object pointer, unless perhaps there is too
   little memory even to allocate the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
   The <CODE
CLASS="FUNCTION"
>PQstatus</CODE
> function should be called to check
   whether a connection was successfully made before queries are sent
   via the connection object.

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
><A
NAME="AEN26494"
></A
></DT
><DD
><P
>       Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQconnectdb(const char *conninfo);</PRE
><P></P
><P
>   This function opens a new database connection using the parameters taken
   from the string <TT
CLASS="LITERAL"
>conninfo</TT
>.  Unlike <CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
> below,
   the parameter set can be extended without changing the function signature,
   so use of this function (or its nonblocking analogues <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>
   and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>) is preferred for new application programming.
   </P
><P
>   The passed 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 <TT
CLASS="LITERAL"
>keyword = value</TT
>.
   Spaces around the equal sign are optional.
   To write an empty value or a value containing
   spaces, surround it with single quotes, e.g.,
   <TT
CLASS="LITERAL"
>keyword = 'a value'</TT
>.
   Single quotes and backslashes within the value must be escaped with a
   backslash, i.e., <TT
CLASS="LITERAL"
>\'</TT
> and <TT
CLASS="LITERAL"
>\\</TT
>.
   </P
><P
>   The currently recognized parameter key words are:

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>host</TT
></DT
><DD
><P
>      Name of host to connect to.<A
NAME="AEN26516"
></A
>
      If this begins with a slash, it specifies Unix-domain
      communication rather than TCP/IP communication; the value is the
      name of the directory in which the socket file is stored.  The
      default behavior when <TT
CLASS="LITERAL"
>host</TT
> is not specified
      is to connect to a Unix-domain
      socket<A
NAME="AEN26519"
></A
> in
      <TT
CLASS="FILENAME"
>/tmp</TT
> (or whatever socket directory was specified
      when <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> was built). On machines without
      Unix-domain sockets, the default is to connect to <TT
CLASS="LITERAL"
>localhost</TT
>.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>hostaddr</TT
></DT
><DD
><P
>      Numeric IP address of host to connect to.  This should be in the
      standard IPv4 address format, e.g., <TT
CLASS="LITERAL"
>172.28.40.9</TT
>.  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.
     </P
><P
>      Using <TT
CLASS="LITERAL"
>hostaddr</TT
> instead of <TT
CLASS="LITERAL"
>host</TT
> allows the
      application to avoid a host name look-up, which may be important in
      applications with time constraints. However, Kerberos authentication
      requires the host name. The following therefore applies: If
      <TT
CLASS="LITERAL"
>host</TT
> is specified without <TT
CLASS="LITERAL"
>hostaddr</TT
>, a host name
      lookup occurs. If <TT
CLASS="LITERAL"
>hostaddr</TT
> is specified without
      <TT
CLASS="LITERAL"
>host</TT
>, the value for <TT
CLASS="LITERAL"
>hostaddr</TT
> gives the remote
      address. When Kerberos is used, a reverse name query occurs to obtain
      the host name for Kerberos. If both
      <TT
CLASS="LITERAL"
>host</TT
> and <TT
CLASS="LITERAL"
>hostaddr</TT
> are specified, the value for
      <TT
CLASS="LITERAL"
>hostaddr</TT
> gives the remote address; the value for
      <TT
CLASS="LITERAL"
>host</TT
> is ignored, unless Kerberos is used, in which case that
      value is used for Kerberos authentication. (Note that authentication is
      likely to fail if <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> is passed a host name
      that is not the name of the machine at <TT
CLASS="LITERAL"
>hostaddr</TT
>.)  Also,
      <TT
CLASS="LITERAL"
>host</TT
> rather than <TT
CLASS="LITERAL"
>hostaddr</TT
> is used to identify
      the connection in <TT
CLASS="FILENAME"
>~/.pgpass</TT
> (see
      <A
HREF="libpq-pgpass.html"
>Section 29.13</A
>).
     </P
><P
>      Without either a host name or host address,
      <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will connect using a
      local Unix-domain socket; or on machines without Unix-domain
      sockets, it will attempt to connect to <TT
CLASS="LITERAL"
>localhost</TT
>.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>port</TT
></DT
><DD
><P
>      Port number to connect to at the server host, or socket file
      name extension for Unix-domain
      connections.<A
NAME="AEN26556"
></A
>
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>dbname</TT
></DT
><DD
><P
>      The database name.  Defaults to be the same as the user name.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>user</TT
></DT
><DD
><P
>      <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> user name to connect as.
      Defaults to be the same as the operating system name of the user
      running the application.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>password</TT
></DT
><DD
><P
>      Password to be used if the server demands password authentication.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>connect_timeout</TT
></DT
><DD
><P
>      Maximum wait for connection, in seconds (write as a decimal integer
      string). Zero or not specified means wait indefinitely.  It is not
      recommended to use a timeout of less than 2 seconds.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>options</TT
></DT
><DD
><P
>       Command-line options to be sent to the server.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>tty</TT
></DT
><DD
><P
>      Ignored (formerly, this specified where to send server debug output).
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>sslmode</TT
></DT
><DD
><P
>       This option determines whether or with what priority an
       <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection will be negotiated with the
       server. There are four modes: <TT
CLASS="LITERAL"
>disable</TT
> will attempt
       only an unencrypted <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection;
       <TT
CLASS="LITERAL"
>allow</TT
> will negotiate, trying first a
       non-<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection, then if that fails, trying an
       <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection; <TT
CLASS="LITERAL"
>prefer</TT
> (the default)
       will negotiate, trying first an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection,
       then if that fails, trying a regular non-<ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
>
       connection; <TT
CLASS="LITERAL"
>require</TT
> will try only an
       <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection.
      </P
><P
>       If <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is compiled without SSL support,
       using option <TT
CLASS="LITERAL"
>require</TT
> will cause an error, while
       options <TT
CLASS="LITERAL"
>allow</TT
> and <TT
CLASS="LITERAL"
>prefer</TT
> will be
       accepted but <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will not in fact attempt
       an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
>
       connection.<A
NAME="AEN26612"
></A
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>requiressl</TT
></DT
><DD
><P
>       This option is deprecated in favor of the <TT
CLASS="LITERAL"
>sslmode</TT
>
       setting.
      </P
><P
>       If set to 1, an <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection to the server
       is required (this is equivalent to <TT
CLASS="LITERAL"
>sslmode</TT
>
       <TT
CLASS="LITERAL"
>require</TT
>).  <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will then refuse
       to connect if the server does not accept an
       <ACRONYM
CLASS="ACRONYM"
>SSL</ACRONYM
> connection.  If set to 0 (default),
       <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> will negotiate the connection type with
       the server (equivalent to <TT
CLASS="LITERAL"
>sslmode</TT
>
       <TT
CLASS="LITERAL"
>prefer</TT
>).  This option is only available if
       <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> is compiled with SSL support.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>krbsrvname</TT
></DT
><DD
><P
>       Kerberos service name to use when authenticating with Kerberos 5.
       This must match the service name specified in the server
       configuration for Kerberos authentication to succeed. (See also
       <A
HREF="auth-methods.html#KERBEROS-AUTH"
>Section 20.2.3</A
>.)
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>service</TT
></DT
><DD
><P
>      Service name to use for additional parameters.  It specifies a service
      name in <TT
CLASS="FILENAME"
>pg_service.conf</TT
> that holds additional connection parameters.
      This allows applications to specify only a service name so connection parameters 
      can be centrally maintained. See <A
HREF="libpq-pgservice.html"
>Section 29.14</A
>.
     </P
></DD
></DL
></DIV
><P>

   If  any  parameter is unspecified, then the corresponding
   environment variable (see <A
HREF="libpq-envars.html"
>Section 29.12</A
>)
   is checked. If the  environment  variable is not set either,
   then the indicated built-in defaults are used.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
><A
NAME="AEN26648"
></A
></DT
><DD
><P
>       Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQsetdbLogin(const char *pghost,
                     const char *pgport,
                     const char *pgoptions,
                     const char *pgtty,
                     const char *dbName,
                     const char *login,
                     const char *pwd);</PRE
><P></P
><P
>   This is the predecessor of <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> with a fixed
   set of parameters.  It has the same functionality except that the
   missing parameters will always take on default values.  Write <TT
CLASS="SYMBOL"
>NULL</TT
> or an
   empty string for any one of the fixed parameters that is to be defaulted.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQsetdb</CODE
><A
NAME="AEN26659"
></A
></DT
><DD
><P
>   Makes a new connection to the database server.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQsetdb(char *pghost,
                char *pgport,
                char *pgoptions,
                char *pgtty,
                char *dbName);</PRE
><P></P
><P
>   This is a macro that calls <CODE
CLASS="FUNCTION"
>PQsetdbLogin</CODE
> with null pointers
   for the <TT
CLASS="PARAMETER"
>login</TT
> and <TT
CLASS="PARAMETER"
>pwd</TT
> parameters.  It is provided
   for backward compatibility with very old programs.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
><A
NAME="AEN26671"
></A
><BR><CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
><A
NAME="AEN26675"
></A
></DT
><DD
><P
>   <A
NAME="AEN26679"
></A
>
   Make a connection to the database server in a nonblocking manner.
</P><PRE
CLASS="SYNOPSIS"
>PGconn *PQconnectStart(const char *conninfo);</PRE
><P>
</P><PRE
CLASS="SYNOPSIS"
>PostgresPollingStatusType PQconnectPoll(PGconn *conn);</PRE
><P></P
><P
>   These two 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
   <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>, and so the application can manage this
   operation in parallel with other activities.
  </P
><P
>   The database connection is made using the parameters taken from the string
   <TT
CLASS="LITERAL"
>conninfo</TT
>, passed to <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>. This string is in
   the same format as described above for <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>.
  </P
><P
>   Neither <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> nor <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> will block, so long as a number of
   restrictions are met:
   <P
></P
></P><UL
><LI
><P
>      The <TT
CLASS="LITERAL"
>hostaddr</TT
> and <TT
CLASS="LITERAL"
>host</TT
> parameters are used appropriately to ensure that
      name and reverse name queries are not made. See the documentation of
      these parameters under <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> above for details.
     </P
></LI
><LI
><P
>      If you call <CODE
CLASS="FUNCTION"
>PQtrace</CODE
>, ensure that the stream object
      into which you trace will not block.
     </P
></LI
><LI
><P
>      You ensure that the socket is in the appropriate state
      before calling <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, as described below.
     </P
></LI
></UL
><P>
  </P
><P
>   To begin a nonblocking connection request, call <TT
CLASS="LITERAL"
>conn = PQconnectStart("<TT
CLASS="REPLACEABLE"
><I
>connection_info_string</I
></TT
>")</TT
>.
   If <TT
CLASS="VARNAME"
>conn</TT
> is null, then <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> has been unable to allocate a new <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
   structure. Otherwise, a valid <TT
CLASS="STRUCTNAME"
>PGconn</TT
> pointer is returned (though not yet
   representing a valid connection to the database). On return from
   <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>, call <TT
CLASS="LITERAL"
>status = PQstatus(conn)</TT
>. If <TT
CLASS="VARNAME"
>status</TT
> equals
   <TT
CLASS="SYMBOL"
>CONNECTION_BAD</TT
>, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> has failed.
  </P
><P
>   If <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> succeeds, the next stage is to poll
   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> so that it may proceed with the connection sequence.
   Use <CODE
CLASS="FUNCTION"
>PQsocket(conn)</CODE
> to obtain the descriptor of the
   socket underlying the database connection.
   Loop thus: If <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> last returned
   <TT
CLASS="SYMBOL"
>PGRES_POLLING_READING</TT
>, wait until the socket is ready to
   read (as indicated by <CODE
CLASS="FUNCTION"
>select()</CODE
>, <CODE
CLASS="FUNCTION"
>poll()</CODE
>, or
   similar system function).
   Then call <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> again.
   Conversely, if <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> last returned
   <TT
CLASS="SYMBOL"
>PGRES_POLLING_WRITING</TT
>, wait until the socket is ready
   to write, then call <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> again.
   If you have yet to call
   <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, i.e., just after the call to
   <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>, behave as if it last returned
   <TT
CLASS="SYMBOL"
>PGRES_POLLING_WRITING</TT
>.  Continue this loop until
   <CODE
CLASS="FUNCTION"
>PQconnectPoll(conn)</CODE
> returns
   <TT
CLASS="SYMBOL"
>PGRES_POLLING_FAILED</TT
>, indicating the connection procedure
   has failed, or <TT
CLASS="SYMBOL"
>PGRES_POLLING_OK</TT
>, indicating the connection
   has been successfully made.
  </P
><P
>    At any time during connection, the status of the connection may be
    checked by calling <CODE
CLASS="FUNCTION"
>PQstatus</CODE
>. If this gives <TT
CLASS="SYMBOL"
>CONNECTION_BAD</TT
>, then the
    connection procedure has failed; if it gives <CODE
CLASS="FUNCTION"
>CONNECTION_OK</CODE
>, then the
    connection is ready.  Both of these states are equally detectable
    from the return value of <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>, described above. Other states may also occur
    during (and only during) an asynchronous connection procedure. These
    indicate the current stage of the connection procedure and may be useful
    to provide feedback to the user for example. These statuses are:

    <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_STARTED</TT
></DT
><DD
><P
>        Waiting for connection to be made.
       </P
></DD
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_MADE</TT
></DT
><DD
><P
>        Connection OK; waiting to send.
       </P
></DD
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_AWAITING_RESPONSE</TT
></DT
><DD
><P
>        Waiting for a response from the server.
       </P
></DD
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_AUTH_OK</TT
></DT
><DD
><P
>        Received authentication; waiting for backend start-up to finish.
       </P
></DD
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_SSL_STARTUP</TT
></DT
><DD
><P
>        Negotiating SSL encryption.
       </P
></DD
><DT
><TT
CLASS="SYMBOL"
>CONNECTION_SETENV</TT
></DT
><DD
><P
>        Negotiating environment-driven parameter settings.
       </P
></DD
></DL
></DIV
><P>

    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:
</P><PRE
CLASS="PROGRAMLISTING"
>switch(PQstatus(conn))
{
    case CONNECTION_STARTED:
        feedback = "Connecting...";
        break;

    case CONNECTION_MADE:
        feedback = "Connected to server...";
        break;
.
.
.
    default:
        feedback = "Connecting...";
}</PRE
><P>
  </P
><P
>   The <TT
CLASS="LITERAL"
>connect_timeout</TT
> connection parameter is ignored
   when using <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>; it is the application's
   responsibility to decide whether an excessive amount of time has elapsed.
   Otherwise, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> followed by a
   <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> loop is equivalent to
   <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
>.
  </P
><P
>   Note that if <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> returns a non-null pointer, you must call
   <CODE
CLASS="FUNCTION"
>PQfinish</CODE
> 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.
  </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQconndefaults</CODE
><A
NAME="AEN26783"
></A
></DT
><DD
><P
>   Returns the default connection options.
</P><PRE
CLASS="SYNOPSIS"
>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;  /* Character to display for 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;</PRE
><P></P
><P
>   Returns a connection options array.  This may be used to determine
   all possible <CODE
CLASS="FUNCTION"
>PQconnectdb</CODE
> options and their
   current default values.  The return value points to an array of
   <TT
CLASS="STRUCTNAME"
>PQconninfoOption</TT
> structures, which ends
   with an entry having a null <TT
CLASS="STRUCTFIELD"
>keyword</TT
> pointer.  The
   null pointer is returned if memory could not be allocated. Note that
   the current default values (<TT
CLASS="STRUCTFIELD"
>val</TT
> fields)
   will depend on environment variables and other context.  Callers
   must treat the connection options data as read-only.
   </P
><P
>    After processing the options array, free it by passing it to
    <CODE
CLASS="FUNCTION"
>PQconninfoFree</CODE
>.  If this is not done, a small amount of memory
    is leaked for each call to <CODE
CLASS="FUNCTION"
>PQconndefaults</CODE
>.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQfinish</CODE
><A
NAME="AEN26799"
></A
></DT
><DD
><P
>   Closes  the  connection to the server.  Also frees
   memory used by the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
</P><PRE
CLASS="SYNOPSIS"
>void PQfinish(PGconn *conn);</PRE
><P></P
><P
>   Note that even if the server connection attempt fails (as
   indicated by <CODE
CLASS="FUNCTION"
>PQstatus</CODE
>), the application should call <CODE
CLASS="FUNCTION"
>PQfinish</CODE
>
   to free the memory used by the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
   The <TT
CLASS="STRUCTNAME"
>PGconn</TT
> pointer must not be used again after
   <CODE
CLASS="FUNCTION"
>PQfinish</CODE
> has been called.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQreset</CODE
><A
NAME="AEN26814"
></A
></DT
><DD
><P
>   Resets the communication channel to the server.
</P><PRE
CLASS="SYNOPSIS"
>void PQreset(PGconn *conn);</PRE
><P></P
><P
>   This function will close the connection
   to the server and attempt to  reestablish  a  new
   connection to the same server, using all the same
   parameters previously used.  This may be useful for
   error recovery if a working connection is lost.
   </P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQresetStart</CODE
><A
NAME="AEN26823"
></A
><BR><CODE
CLASS="FUNCTION"
>PQresetPoll</CODE
><A
NAME="AEN26827"
></A
></DT
><DD
><P
>   Reset the communication channel to the server, in a nonblocking manner.
</P><PRE
CLASS="SYNOPSIS"
>int PQresetStart(PGconn *conn);</PRE
><P>
</P><PRE
CLASS="SYNOPSIS"
>PostgresPollingStatusType PQresetPoll(PGconn *conn);</PRE
><P></P
><P
>    These functions will close the connection to the server and attempt to
    reestablish a new connection to the same server, using all the same
    parameters previously used. This may be useful for error recovery if a
    working connection is lost. They differ from <CODE
CLASS="FUNCTION"
>PQreset</CODE
> (above) in that they
    act in a nonblocking manner. These functions suffer from the same
    restrictions as <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>.
   </P
><P
>    To initiate a connection reset, call <CODE
CLASS="FUNCTION"
>PQresetStart</CODE
>. If it returns 0, the reset has failed. If it returns 1,
    poll the reset using <CODE
CLASS="FUNCTION"
>PQresetPoll</CODE
> in exactly the same way as you would
    create the connection using <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
>.
   </P
></DD
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