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Postgres FD Implementation
Commit b7f61685 authored by Thomas G. Lockhart's avatar Thomas G. Lockhart
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<Chapter Id="libpq-chapter">
<Title id="libpq">libpq</Title>
<Para>
<FileName>libpq</FileName> is the <acronym>C</acronym> application programmer's interface to
<ProductName>PostgreSQL</ProductName>. <FileName>libpq</FileName> is a set
of library routines that allow client programs to pass queries to the
<ProductName>Postgres</ProductName> backend server and to receive the
results of these queries. <FileName>libpq</FileName> is also the
underlying engine for several other <ProductName>PostgreSQL</ProductName>
application interfaces, including <FileName>libpq++</FileName> (C++),
<FileName>libpgtcl</FileName> (Tcl), <ProductName>Perl</ProductName>, and
<FileName>ecpg</FileName>. So some aspects of libpq's behavior will be
important to you if you use one of those packages.
Three short programs are included at the end of this section to show how
to write programs that use <FileName>libpq</FileName>. There are several
complete examples of <FileName>libpq</FileName> applications in the
following directories:
<ProgramListing>
../src/test/regress
../src/test/examples
../src/bin/psql
</ProgramListing>
</Para>
<Para>
Frontend programs which use <FileName>libpq</FileName> must include the
header file <FileName>libpq-fe.h</FileName> and must link with the
<FileName>libpq</FileName> library.
</Para>
<Sect1>
<Title>Database Connection Functions</Title>
<Para>
The following routines deal with making a connection to
a <ProductName>Postgres</ProductName> backend server. The application
program can have several backend connections open at one time.
(One reason to do that is to access more than one database.)
Each connection is represented by a PGconn object which is obtained
from PQconnectdb() or PQsetdbLogin(). Note that these functions
will always return a non-null object pointer, unless perhaps
there is too little memory even to allocate the PGconn object.
The PQstatus function should be called
to check whether a connection was successfully made
before queries are sent via the connection object.
<ItemizedList>
<ListItem>
<Para>
<Function>PQconnectdb</Function>
Makes a new connection to the database server.
<synopsis>
<chapter id="libpq-chapter">
<title id="libpq">libpq</title>
<para>
<filename>libpq</filename> is the <acronym>C</acronym>
application programmer's interface to
<productname>PostgreSQL</productname>. <filename>libpq</filename> is a set
of library routines that allow client programs to pass queries to the
<productname>Postgres</productname> backend server and to receive the
results of these queries. <filename>libpq</filename> is also the
underlying engine for several other <productname>PostgreSQL</productname>
application interfaces, including <filename>libpq++</filename> (C++),
<filename>libpgtcl</filename> (Tcl), <productname>Perl</productname>, and
<filename>ecpg</filename>. So some aspects of libpq's behavior will be
important to you if you use one of those packages.
</para>
<para>
Three short programs are included at the end of this section to show how
to write programs that use <filename>libpq</filename>. There are several
complete examples of <filename>libpq</filename> applications in the
following directories:
<programlisting>
../src/test/regress
../src/test/examples
../src/bin/psql
</programlisting>
</para>
<para>
Frontend programs which use <filename>libpq</filename> must include the
header file <filename>libpq-fe.h</filename> and must link with the
<filename>libpq</filename> library.
</para>
<sect1>
<title>Database Connection Functions</title>
<para>
The following routines deal with making a connection to
a <productname>Postgres</productname> backend server. The application
program can have several backend connections open at one time.
(One reason to do that is to access more than one database.)
Each connection is represented by a PGconn object which is obtained
from PQconnectdb() or PQsetdbLogin(). Note that these functions
will always return a non-null object pointer, unless perhaps
there is too little memory even to allocate the PGconn object.
The PQstatus function should be called
to check whether a connection was successfully made
before queries are sent via the connection object.
<itemizedlist>
<listitem>
<para>
<function>PQconnectdb</function>
Makes a new connection to the database server.
<synopsis>
PGconn *PQconnectdb(const char *conninfo)
</synopsis>
</synopsis>
This routine opens a new database connection using the parameters taken
from the string <literal>conninfo</literal>. Unlike PQsetdbLogin() below,
the parameter set can be extended without changing the function signature,
......@@ -64,8 +66,9 @@ PGconn *PQconnectdb(const char *conninfo)
/ PQconnectPoll is prefered for application programming. The passed string
can be empty to use all default parameters, or it can contain one or more
parameter settings separated by whitespace.
</Para>
<Para>
</para>
<para>
Each parameter setting is in the form <literal>keyword = value</literal>.
(To write a null value or a value containing
spaces, surround it with single quotes, e.g.,
......@@ -74,27 +77,28 @@ PGconn *PQconnectdb(const char *conninfo)
Spaces around the equal sign are optional.) The currently recognized
parameter keywords are:
<VariableList>
<VarListEntry>
<variablelist>
<varlistentry>
<term><literal>host</literal></term>
<ListItem>
<Para>
Name of host to connect to. If a non-zero-length string is specified, TCP/IP
<listitem>
<para>
Name of host to connect to. If a non-zero-length string is
specified, TCP/IP
communication is used. Using this parameter causes a hostname look-up.
See hostaddr.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>hostaddr</literal></term>
<ListItem>
<Para>
<listitem>
<para>
IP address of host to connect to. This should be in standard
numbers-and-dots form, as used by the BSD functions inet_aton et al. If
a non-zero-length string is specified, TCP/IP communication is used.
</Para>
<Para>
</para>
<para>
Using hostaddr instead of host 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
......@@ -107,69 +111,69 @@ PGconn *PQconnectdb(const char *conninfo)
is used for Kerberos authentication. Note that authentication is likely
to fail if libpq is passed a host name which is not the name of the
machine at hostaddr.
</Para>
<Para>
</para>
<para>
Without both a host name and host address, libpq will connect using a
local Unix domain socket.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>port</literal></term>
<ListItem>
<Para>
<listitem>
<para>
Port number to connect to at the server host,
or socket filename extension for Unix-domain connections.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>dbname</literal></term>
<ListItem>
<Para>
<listitem>
<para>
The database name.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>user</literal></term>
<ListItem>
<Para>
<listitem>
<para>
User name to connect as.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>password</literal></term>
<ListItem>
<Para>
<listitem>
<para>
Password to be used if the server demands password authentication.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>options</literal></term>
<ListItem>
<Para>
<listitem>
<para>
Trace/debug options to be sent to the server.
</Para>
</ListItem>
</VarListEntry>
</para>
</listitem>
</varlistentry>
<VarListEntry>
<varlistentry>
<term><literal>tty</literal></term>
<ListItem>
<Para>
<listitem>
<para>
A file or tty for optional debug output from the backend.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</para>
</listitem>
</varlistentry>
</variablelist>
If any parameter is unspecified, then the corresponding
environment variable (see "Environment Variables" section)
......@@ -177,15 +181,16 @@ PGconn *PQconnectdb(const char *conninfo)
then hardwired defaults are used.
The return value is a pointer to an abstract struct
representing the connection to the backend.
</Para>
<Para>
</para>
<para>
This function is not thread-safe.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQsetdbLogin</Function> Makes a new connection to the database server.
<listitem>
<para>
<function>PQsetdbLogin</function>
Makes a new connection to the database server.
<synopsis>
PGconn *PQsetdbLogin(const char *pghost,
const char *pgport,
......@@ -198,15 +203,15 @@ PGconn *PQsetdbLogin(const char *pghost,
This is the predecessor of <function>PQconnectdb</function> with a fixed number
of parameters but the same functionality.
</Para>
<Para>
</para>
<para>
This function is not thread-safe.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQsetdb</Function> Makes a new connection to the database server.
<listitem>
<para>
<function>PQsetdb</function> Makes a new connection to the database server.
<synopsis>
PGconn *PQsetdb(char *pghost,
char *pgport,
......@@ -217,13 +222,13 @@ PGconn *PQsetdb(char *pghost,
This is a macro that calls <function>PQsetdbLogin()</function> with null pointers
for the login and pwd parameters. It is provided primarily
for backward compatibility with old programs.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQconnectStart</Function>
<Function>PQconnectPoll</Function>
<listitem>
<para>
<function>PQconnectStart</function>
<function>PQconnectPoll</function>
Make a connection to the database server in a non-blocking manner.
<synopsis>
PGconn *PQconnectStart(const char *conninfo)
......@@ -234,49 +239,49 @@ PostgresPollingStatusType *PQconnectPoll(PQconn *conn)
These two routines 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.
</Para>
<Para>
</para>
<para>
The database connection is made using the parameters taken from the string
<literal>conninfo</literal>, passed to PQconnectStart. This string is in
the same format as described above for PQconnectdb.
</Para>
<Para>
</para>
<para>
Neither PQconnectStart nor PQconnectPoll will block, as long as a number of
restrictions are met:
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
The hostaddr and host parameters are used appropriately to ensure that
name and reverse name queries are not made. See the documentation of
these parameters under PQconnectdb above for details.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<listitem>
<para>
If you call PQtrace, ensure that the stream object into which you trace
will not block.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<listitem>
<para>
You ensure for yourself that the socket is in the appropriate state
before calling PQconnectPoll, as described below.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
To begin, call conn=PQconnectStart("&lt;connection_info_string&gt;"). If
conn is NULL, then libpq has been unable to allocate a new PGconn
structure. Otherwise, a valid PGconn pointer is returned (though not yet
representing a valid connection to the database). On return from
PQconnectStart, call status=PQstatus(conn). If status equals
CONNECTION_BAD, PQconnectStart has failed.
</Para>
<Para>
</para>
<para>
If PQconnectStart succeeds, the next stage is to poll libpq so that it may
proceed with the connection sequence. Loop thus: Consider a connection
'inactive' by default. If PQconnectPoll last returned PGRES_POLLING_ACTIVE,
......@@ -290,13 +295,13 @@ PostgresPollingStatusType *PQconnectPoll(PQconn *conn)
again. If this call returns PGRES_POLLING_FAILED, the connection procedure
has failed. If this call returns PGRES_POLLING_OK, the connection has been
successfully made.
</Para>
<Para>
</para>
<para>
Note that the use of select() to ensure that the socket is ready is merely
a (likely) example; those with other facilities available, such as a
poll() call, may of course use that instead.
</Para>
<Para>
</para>
<para>
At any time during connection, the status of the connection may be
checked, by calling PQstatus. If this is CONNECTION_BAD, then the
connection procedure has failed; if this is CONNECTION_OK, then the
......@@ -305,50 +310,50 @@ PostgresPollingStatusType *PQconnectPoll(PQconn *conn)
shown 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 may include:
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
CONNECTION_STARTED: Waiting for connection to be made.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_MADE: Connection OK; waiting to send.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_AWAITING_RESPONSE: Waiting for a response from the backend.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_AUTH_RESPONSE: Got an authentication response; about to deal
with it.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_ERROR_RESPONSE: Got an error response; about to deal with it.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_AUTH_OK: Received authentication; waiting for ReadyForQuery etc.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
CONNECTION_SETENV: Negotiating environment.
</Para>
</ListItem>
</ItemizedList>
</para>
</listitem>
</itemizedlist>
Note that, although these constants will remain (in order to maintain
compatibility) an application should never rely upon these appearing in a
particular order, or at all, or on the status always being one of these
documented values. An application may do something like this:
<ProgramListing>
<programlisting>
switch(PQstatus(conn))
{
case CONNECTION_STARTED:
......@@ -364,32 +369,32 @@ PostgresPollingStatusType *PQconnectPoll(PQconn *conn)
default:
feedback = "Connecting...";
}
</ProgramListing>
</Para>
<Para>
</programlisting>
</para>
<para>
Note that if PQconnectStart returns a non-NULL pointer, you must call
PQfinish upon that, when you are finished with it, in order to dispose of
the structure and any associated memory blocks. This must be done even if a
call to PQconnectStart or PQconnectPoll failed.
</Para>
<Para>
</para>
<para>
PQconnectPoll will currently block if libpq is compiled with USE_SSL
defined. This restriction may be removed in the future.
</Para>
<Para>
</para>
<para>
PQconnectPoll will currently block under Windows, unless libpq is compiled
with WIN32_NON_BLOCKING_CONNECTIONS defined. This code has not yet been
tested under Windows, and so it is currently off by default. This may be
changed in the future.
</Para>
<Para>
</para>
<para>
These functions are not thread-safe.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQconndefaults</Function> Returns the default connection options.
<listitem>
<para>
<function>PQconndefaults</function> Returns the default connection options.
<synopsis>
PQconninfoOption *PQconndefaults(void)
......@@ -416,15 +421,15 @@ struct PQconninfoOption
keyword pointer. Note that the default values ("val" fields)
will depend on environment variables and other context.
Callers must treat the connection options data as read-only.
</Para>
<Para>
</para>
<para>
This function is not thread-safe.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQfinish</Function>
<listitem>
<para>
<function>PQfinish</function>
Close the connection to the backend. Also frees
memory used by the PGconn object.
<synopsis>
......@@ -434,12 +439,12 @@ void PQfinish(PGconn *conn)
indicated by PQstatus), the application should call PQfinish
to free the memory used by the PGconn object.
The PGconn pointer should not be used after PQfinish has been called.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQreset</Function>
<listitem>
<para>
<function>PQreset</function>
Reset the communication port with the backend.
<synopsis>
void PQreset(PGconn *conn)
......@@ -449,13 +454,13 @@ void PQreset(PGconn *conn)
connection to the same postmaster, using all the same
parameters previously used. This may be useful for
error recovery if a working connection is lost.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQresetStart</Function>
<Function>PQresetPoll</Function>
<listitem>
<para>
<function>PQresetStart</function>
<function>PQresetPoll</function>
Reset the communication port with the backend, in a non-blocking manner.
<synopsis>
int PQresetStart(PGconn *conn);
......@@ -469,31 +474,31 @@ PostgresPollingStatusType PQresetPoll(PGconn *conn);
working connection is lost. They differ from PQreset (above) in that they
act in a non-blocking manner. These functions suffer from the same
restrictions as PQconnectStart and PQconnectPoll.
</Para>
<Para>
</para>
<para>
Call PQresetStart. If it returns 0, the reset has failed. If it returns 1,
poll the reset using PQresetPoll in exactly the same way as you would
create the connection using PQconnectPoll.
</Para>
</ListItem>
</para>
</listitem>
</ItemizedList>
</Para>
</itemizedlist>
</para>
<Para>
<para>
libpq application programmers should be careful to
maintain the PGconn abstraction. Use the accessor functions below to get
at the contents of PGconn. Avoid directly referencing the fields of the
PGconn structure because they are subject to change in the future.
(Beginning in <ProductName>PostgreSQL</ProductName> release 6.4, the
(Beginning in <productname>PostgreSQL</productname> release 6.4, the
definition of struct PGconn is not even provided in <filename>libpq-fe.h</filename>.
If you have old code that accesses PGconn fields directly, you can keep using it
by including <filename>libpq-int.h</filename> too, but you are encouraged to fix the code
soon.)
<ItemizedList>
<ListItem>
<Para>
<Function>PQdb</Function>
<itemizedlist>
<listitem>
<para>
<function>PQdb</function>
Returns the database name of the connection.
<synopsis>
const char *PQdb(const PGconn *conn)
......@@ -501,196 +506,215 @@ const char *PQdb(const PGconn *conn)
PQdb and the next several functions return the values established
at connection. These values are fixed for the life of the PGconn
object.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQuser</Function>
<listitem>
<para>
<function>PQuser</function>
Returns the user name of the connection.
<synopsis>
const char *PQuser(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQpass</Function>
<listitem>
<para>
<function>PQpass</function>
Returns the password of the connection.
<synopsis>
const char *PQpass(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQhost</Function>
<listitem>
<para>
<function>PQhost</function>
Returns the server host name of the connection.
<synopsis>
const char *PQhost(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQport</Function>
<listitem>
<para>
<function>PQport</function>
Returns the port of the connection.
<synopsis>
const char *PQport(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQtty</Function>
<listitem>
<para>
<function>PQtty</function>
Returns the debug tty of the connection.
<synopsis>
const char *PQtty(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQoptions</Function>
<listitem>
<para>
<function>PQoptions</function>
Returns the backend options used in the connection.
<synopsis>
const char *PQoptions(const PGconn *conn)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQstatus</Function>
<listitem>
<para>
<function>PQstatus</function>
Returns the status of the connection.
<synopsis>
ConnStatusType PQstatus(const PGconn *conn)
</synopsis>
</Para>
<Para>
The status can be one of a number of values. However, only two of these are
seen outside of an asynchronous connection procedure -
<literal>CONNECTION_OK</literal> or <literal>CONNECTION_BAD</literal>. A good
connection to the database has the status CONNECTION_OK. A failed connection
attempt is signaled by status <literal>CONNECTION_BAD</literal>. Ordinarily,
an OK status will remain so until <function>PQfinish</function>, but a
communications failure might result in the status changing to
<literal>CONNECTION_BAD</literal> prematurely. In that case the application
could try to recover by calling <function>PQreset</function>.
</Para>
<Para>
See the entry for PQconnectStart and PQconnectPoll with regards to other status codes
that might be seen.
</ListItem>
<ListItem>
<Para>
<Function>PQerrorMessage</Function>
Returns the error message most recently generated by
an operation on the connection.
<synopsis>
</para>
<para>
The status can be one of a number of values.
However, only two of these are
seen outside of an asynchronous connection procedure -
<literal>CONNECTION_OK</literal> or
<literal>CONNECTION_BAD</literal>. A good
connection to the database has the status CONNECTION_OK.
A failed connection
attempt is signaled by status
<literal>CONNECTION_BAD</literal>.
Ordinarily, an OK status will remain so until
<function>PQfinish</function>, but a
communications failure might result in the status changing to
<literal>CONNECTION_BAD</literal> prematurely.
In that case the application
could try to recover by calling <function>PQreset</function>.
</para>
<para>
See the entry for PQconnectStart and PQconnectPoll with regards
to other status codes
that might be seen.
</para>
</listitem>
<listitem>
<para>
<function>PQerrorMessage</function>
Returns the error message most recently generated by
an operation on the connection.
<synopsis>
const char *PQerrorMessage(const PGconn* conn);
</synopsis>
</Para>
<Para>
Nearly all libpq functions will set <function>PQerrorMessage</function> if they fail.
Note that by libpq convention, a non-empty <function>PQerrorMessage</function> will
include a trailing newline.
</Para>
</ListItem>
<ListItem>
<Para>
<Function>PQbackendPID</Function>
Returns the process <acronym>ID</acronym> of the backend server handling this
connection.
<synopsis>
</synopsis>
</para>
<para>
Nearly all libpq functions will set
<function>PQerrorMessage</function> if they fail.
Note that by libpq convention, a non-empty
<function>PQerrorMessage</function> will
include a trailing newline.
</para>
</listitem>
<listitem>
<para>
<function>PQbackendPID</function>
Returns the process <acronym>ID</acronym> of the backend server
handling this connection.
<synopsis>
int PQbackendPID(const PGconn *conn);
</synopsis>
The backend <acronym>PID</acronym> is useful for debugging purposes and for comparison
to NOTIFY messages (which include the <acronym>PID</acronym> of the notifying backend).
Note that the <acronym>PID</acronym> belongs to a process executing on the database
server host, not the local host!
</Para>
</ListItem>
<ListItem>
<Para>
<Function>PQsetenvStart</Function>
<Function>PQsetenvPoll</Function>
<Function>PQsetenvAbort</Function>
Perform an environment negotiation.
<synopsis>
</synopsis>
The backend <acronym>PID</acronym> is useful for debugging
purposes and for comparison
to NOTIFY messages (which include the <acronym>PID</acronym> of
the notifying backend).
Note that the <acronym>PID</acronym> belongs to a process
executing on the database
server host, not the local host!
</para>
</listitem>
<listitem>
<para>
<function>PQsetenvStart</function>
<function>PQsetenvPoll</function>
<function>PQsetenvAbort</function>
Perform an environment negotiation.
<synopsis>
PGsetenvHandle *PQsetenvStart(PGconn *conn)
</synopsis>
<synopsis>
</synopsis>
<synopsis>
PostgresPollingStatusType *PQsetenvPoll(PGsetenvHandle handle)
</synopsis>
<synopsis>
</synopsis>
<synopsis>
void PQsetenvAbort(PGsetenvHandle handle)
</synopsis>
These two routines can be used to re-perform the environment negotiation
that occurs during the opening of a connection to a database server. I have
no idea why this might be useful (XXX anyone?) but it might prove useful
for users to be able to reconfigure their character encodings on-the-fly,
for example.
</Para>
<Para>
These functions will not block, subject to the restrictions applied to
PQconnectStart and PQconnectPoll.
</Para>
<Para>
To begin, call handle=PQsetenvStart(conn), where conn is an open connection
to the database server. If handle is NULL, then libpq has been unable to
allocate a new PGsetenvHandle structure. Otherwise, a valid handle is
returned. This handle is intended to be opaque - you may only use it to
call other functions in libpq (PQsetenvPoll, for example).
</Para>
<Para>
Poll the procedure using PQsetenvPoll, in exactly the same way as you would
create a connection using PQconnectPoll.
</Para>
<Para>
The procedure may be aborted at any time by calling PQsetenvAbort(handle).
</Para>
<Para>
These functions are not thread-safe.
</Para>
</ListItem>
<ListItem>
<Para>
<Function>PQsetenv</Function>
Perform an environment negotiation.
<synopsis>
</synopsis>
These two routines can be used to re-perform the environment negotiation
that occurs during the opening of a connection to a database
server. I have
no idea why this might be useful (XXX anyone?) but it might prove useful
for users to be able to reconfigure their character encodings
on-the-fly, for example.
</para>
<para>
These functions will not block, subject to the restrictions applied to
PQconnectStart and PQconnectPoll.
</para>
<para>
To begin, call handle=PQsetenvStart(conn), where conn is an open connection
to the database server. If handle is NULL, then libpq has been unable to
allocate a new PGsetenvHandle structure. Otherwise, a valid handle is
returned. This handle is intended to be opaque - you may only use it to
call other functions in libpq (PQsetenvPoll, for example).
</para>
<para>
Poll the procedure using PQsetenvPoll, in exactly the same way as you would
create a connection using PQconnectPoll.
</para>
<para>
The procedure may be aborted at any time by calling PQsetenvAbort(handle).
</para>
<para>
These functions are not thread-safe.
</para>
</listitem>
<listitem>
<para>
<function>PQsetenv</function>
Perform an environment negotiation.
<synopsis>
int PQsetenv(PGconn *conn)
</synopsis>
This function performs the same duties as PQsetenvStart and PQsetenvPoll, but
blocks to do so. It returns 1 on success and 0 on failure.
</Para>
</ItemizedList>
</Para>
</Sect1>
<Sect1>
<Title>Query Execution Functions</Title>
<Para>
</synopsis>
This function performs the same duties as PQsetenvStart and
PQsetenvPoll, but
blocks to do so. It returns 1 on success and 0 on failure.
</para>
</listitem>
</itemizedlist>
</para>
</sect1>
<sect1>
<title>Query Execution Functions</title>
<para>
Once a connection to a database server has been successfully
established, the functions described here are used to perform
SQL queries and commands.
<ItemizedList>
<ListItem>
<Para>
<Function>PQexec</Function>
Submit a query to <ProductName>Postgres</ProductName>
<itemizedlist>
<listitem>
<para>
<function>PQexec</function>
Submit a query to <productname>Postgres</productname>
and wait for the result.
<synopsis>
PGresult *PQexec(PGconn *conn,
......@@ -703,59 +727,59 @@ PGresult *PQexec(PGconn *conn,
If a NULL is returned, it
should be treated like a PGRES_FATAL_ERROR result. Use
PQerrorMessage to get more information about the error.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
The <Function>PGresult</Function> structure encapsulates the query result
<para>
The <function>PGresult</function> structure encapsulates the query result
returned by the backend.
<FileName>libpq</FileName> application programmers should be careful to
<filename>libpq</filename> application programmers should be careful to
maintain the PGresult abstraction. Use the accessor functions below to get
at the contents of PGresult. Avoid directly referencing the fields of the
PGresult structure because they are subject to change in the future.
(Beginning in <ProductName>Postgres</ProductName> release 6.4, the
(Beginning in <productname>Postgres</productname> release 6.4, the
definition of struct PGresult is not even provided in libpq-fe.h. If you
have old code that accesses PGresult fields directly, you can keep using it
by including libpq-int.h too, but you are encouraged to fix the code
soon.)
<ItemizedList>
<ListItem>
<Para>
<Function>PQresultStatus</Function>
<itemizedlist>
<listitem>
<para>
<function>PQresultStatus</function>
Returns the result status of the query.
<synopsis>
ExecStatusType PQresultStatus(const PGresult *res)
</synopsis>
PQresultStatus can return one of the following values:
<ItemizedList>
<ListItem>
<Para><literal>PGRES_EMPTY_QUERY</literal> -- The string sent to the backend was empty.</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_COMMAND_OK</literal> -- Successful completion of a command returning no data</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_TUPLES_OK</literal> -- The query successfully executed</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_COPY_OUT</literal> -- Copy Out (from server) data transfer started</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_COPY_IN</literal> -- Copy In (to server) data transfer started</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_BAD_RESPONSE</literal> -- The server's response was not understood</Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_NONFATAL_ERROR</literal></Para>
</ListItem>
<ListItem>
<Para><literal>PGRES_FATAL_ERROR</literal></Para>
</ListItem>
</ItemizedList>
<itemizedlist>
<listitem>
<para><literal>PGRES_EMPTY_QUERY</literal> -- The string sent to the backend was empty.</para>
</listitem>
<listitem>
<para><literal>PGRES_COMMAND_OK</literal> -- Successful completion of a command returning no data</para>
</listitem>
<listitem>
<para><literal>PGRES_TUPLES_OK</literal> -- The query successfully executed</para>
</listitem>
<listitem>
<para><literal>PGRES_COPY_OUT</literal> -- Copy Out (from server) data transfer started</para>
</listitem>
<listitem>
<para><literal>PGRES_COPY_IN</literal> -- Copy In (to server) data transfer started</para>
</listitem>
<listitem>
<para><literal>PGRES_BAD_RESPONSE</literal> -- The server's response was not understood</para>
</listitem>
<listitem>
<para><literal>PGRES_NONFATAL_ERROR</literal></para>
</listitem>
<listitem>
<para><literal>PGRES_FATAL_ERROR</literal></para>
</listitem>
</itemizedlist>
If the result status is <literal>PGRES_TUPLES_OK</literal>, then the
routines described below can be used to retrieve the
......@@ -764,23 +788,23 @@ happens to retrieve zero tuples still shows <literal>PGRES_TUPLES_OK</literal>.
<literal>PGRES_COMMAND_OK</literal> is for commands that can never return tuples
(INSERT, UPDATE, etc.). A response of <literal>PGRES_EMPTY_QUERY</literal> often
exposes a bug in the client software.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQresStatus</Function>
<listitem>
<para>
<function>PQresStatus</function>
Converts the enumerated type returned by PQresultStatus into
a string constant describing the status code.
<synopsis>
const char *PQresStatus(ExecStatusType status);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQresultErrorMessage</Function>
<listitem>
<para>
<function>PQresultErrorMessage</function>
returns the error message associated with the query, or an empty string
if there was no error.
<synopsis>
......@@ -794,75 +818,75 @@ until destroyed, whereas the connection's error message will change when
subsequent operations are done. Use <function>PQresultErrorMessage</function> when you want to
know the status associated with a particular PGresult; use <function>PQerrorMessage</function>
when you want to know the status from the latest operation on the connection.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQntuples</Function>
<listitem>
<para>
<function>PQntuples</function>
Returns the number of tuples (instances)
in the query result.
<synopsis>
int PQntuples(const PGresult *res);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQnfields</Function>
<listitem>
<para>
<function>PQnfields</function>
Returns the number of fields
(attributes) in each tuple of the query result.
<synopsis>
int PQnfields(const PGresult *res);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQbinaryTuples</Function>
<listitem>
<para>
<function>PQbinaryTuples</function>
Returns 1 if the PGresult contains binary tuple data,
0 if it contains ASCII data.
<synopsis>
int PQbinaryTuples(const PGresult *res);
</synopsis>
Currently, binary tuple data can only be returned by a query that
extracts data from a <Acronym>BINARY</Acronym> cursor.
</Para>
</ListItem>
extracts data from a <acronym>BINARY</acronym> cursor.
</para>
</listitem>
<ListItem>
<Para>
<Function>PQfname</Function>
<listitem>
<para>
<function>PQfname</function>
Returns the field (attribute) name associated with the given field index.
Field indices start at 0.
<synopsis>
const char *PQfname(const PGresult *res,
int field_index);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQfnumber</Function>
<listitem>
<para>
<function>PQfnumber</function>
Returns the field (attribute) index
associated with the given field name.
<synopsis>
int PQfnumber(const PGresult *res,
const char *field_name);
</synopsis>
</Para>
</para>
<Para>
<para>
-1 is returned if the given name does not match any field.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQftype</Function>
<listitem>
<para>
<function>PQftype</function>
Returns the field type associated with the
given field index. The integer returned is an
internal coding of the type. Field indices start
......@@ -875,12 +899,12 @@ You can query the system table <literal>pg_type</literal> to obtain
the name and properties of the various datatypes. The <acronym>OID</acronym>s
of the built-in datatypes are defined in <filename>src/include/catalog/pg_type.h</filename>
in the source tree.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQfsize</Function>
<listitem>
<para>
<function>PQfsize</function>
Returns the size in bytes of the field
associated with the given field index.
Field indices start at 0.
......@@ -891,12 +915,12 @@ int PQfsize(const PGresult *res,
PQfsize returns the space allocated for this field in a database
tuple, in other words the size of the server's binary representation
of the data type. -1 is returned if the field is variable size.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQfmod</Function>
<listitem>
<para>
<function>PQfmod</function>
Returns the type-specific modification data of the field
associated with the given field index.
Field indices start at 0.
......@@ -904,12 +928,12 @@ int PQfsize(const PGresult *res,
int PQfmod(const PGresult *res,
int field_index);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQgetvalue</Function>
<listitem>
<para>
<function>PQgetvalue</function>
Returns a single field (attribute) value of one tuple
of a PGresult.
Tuple and field indices start at 0.
......@@ -932,12 +956,12 @@ part of the PGresult structure. One should not modify it,
and one must explicitly
copy the value into other storage if it is to
be used past the lifetime of the PGresult structure itself.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQgetlength</Function>
<listitem>
<para>
<function>PQgetlength</function>
Returns the length of a field (attribute) in bytes.
Tuple and field indices start at 0.
<synopsis>
......@@ -948,12 +972,12 @@ int PQgetlength(const PGresult *res,
This is the actual data length for the particular data value, that is the
size of the object pointed to by PQgetvalue. Note that for ASCII-represented
values, this size has little to do with the binary size reported by PQfsize.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQgetisnull</Function>
<listitem>
<para>
<function>PQgetisnull</function>
Tests a field for a NULL entry.
Tuple and field indices start at 0.
<synopsis>
......@@ -965,23 +989,23 @@ int PQgetisnull(const PGresult *res,
it contains a non-null value. (Note that PQgetvalue
will return an empty string, not a null pointer, for a NULL
field.)
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQcmdStatus</Function>
<listitem>
<para>
<function>PQcmdStatus</function>
Returns the command status string from the SQL command that
generated the PGresult.
<synopsis>
const char * PQcmdStatus(const PGresult *res);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQcmdTuples</Function>
<listitem>
<para>
<function>PQcmdTuples</function>
Returns the number of rows affected by the SQL command.
<synopsis>
const char * PQcmdTuples(const PGresult *res);
......@@ -990,24 +1014,24 @@ const char * PQcmdTuples(const PGresult *res);
PGresult was INSERT, UPDATE or DELETE, this returns a
string containing the number of rows affected. If the
command was anything else, it returns the empty string.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQoidValue</Function>
<listitem>
<para>
<function>PQoidValue</function>
Returns the object id of the tuple
inserted, if the <acronym>SQL</acronym> command was an INSERT.
Otherwise, returns <literal>InvalidOid</literal>.
<synopsis>
Oid PQoidValue(const PGresult *res);
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQoidStatus</Function>
<listitem>
<para>
<function>PQoidStatus</function>
Returns a string with the object id of the tuple
inserted, if the <acronym>SQL</acronym> command was an INSERT.
Otherwise, returns an empty string.
......@@ -1015,12 +1039,12 @@ Oid PQoidValue(const PGresult *res);
const char * PQoidStatus(const PGresult *res);
</synopsis>
The function is deprecated in favor of <function>PQoidValue</function>.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQprint</Function>
<listitem>
<para>
<function>PQprint</function>
Prints out all the tuples and, optionally, the
attribute names to the specified output stream.
<synopsis>
......@@ -1042,14 +1066,14 @@ struct _PQprintOpt {
}
</synopsis>
This function is intended to replace PQprintTuples(), which is
now obsolete. The <FileName>psql</FileName> program uses
now obsolete. The <filename>psql</filename> program uses
<function>PQprint()</function> to display query results.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQprintTuples</Function>
<listitem>
<para>
<function>PQprintTuples</function>
Prints out all the tuples and, optionally, the
attribute names to the specified output stream.
<synopsis>
......@@ -1059,12 +1083,12 @@ void PQprintTuples(const PGresult *res,
int terseOutput, /* delimiter bars or not?*/
int width); /* width of column, variable width if 0*/
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQdisplayTuples</Function>
<listitem>
<para>
<function>PQdisplayTuples</function>
Prints out all the tuples and, optionally, the
attribute names to the specified output stream.
<synopsis>
......@@ -1078,11 +1102,11 @@ void PQdisplayTuples(const PGresult* res,
<function>PQdisplayTuples()</function> was intended to supersede
<function>PQprintTuples()</function>, and
is in turn superseded by <function>PQprint()</function>.
</Para>
</ListItem>
<ListItem>
<Para>
<Function>PQclear</Function>
</para>
</listitem>
<listitem>
<para>
<function>PQclear</function>
Frees the storage associated with the PGresult.
Every query result should be freed via PQclear when
it is no longer needed.
......@@ -1094,12 +1118,12 @@ void PQclear(PQresult *res);
nor even if you close the connection. To get rid of it,
you must call <function>PQclear</function>. Failure to do this will
result in memory leaks in the frontend application.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQmakeEmptyPGresult</Function>
<listitem>
<para>
<function>PQmakeEmptyPGresult</function>
Constructs an empty PGresult object with the given status.
<synopsis>
PGresult* PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status);
......@@ -1111,56 +1135,56 @@ status) themselves. If conn is not NULL and status indicates an error,
the connection's current errorMessage is copied into the PGresult.
Note that PQclear should eventually be called on the object, just
as with a PGresult returned by libpq itself.
</Para>
</ListItem>
</para>
</listitem>
</ItemizedList>
</Para>
</Sect1>
</itemizedlist>
</para>
</sect1>
<Sect1>
<Title>Asynchronous Query Processing</Title>
<sect1>
<title>Asynchronous Query Processing</title>
<Para>
<para>
The <function>PQexec</function> function is adequate for submitting queries in
simple synchronous
applications. It has a couple of major deficiencies however:
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
<function>PQexec</function> waits for the query to be completed. The application may have other
work to do (such as maintaining a user interface), in which case it won't
want to block waiting for the response.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
Since control is buried inside <function>PQexec</function>, it is hard for the frontend
to decide it would like to try to cancel the ongoing query. (It can be
done from a signal handler, but not otherwise.)
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<function>PQexec</function> can return only one PGresult structure. If the submitted query
string contains multiple <acronym>SQL</acronym> commands, all but the last PGresult are
discarded by <function>PQexec</function>.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
Applications that do not like these limitations can instead use the
underlying functions that <function>PQexec</function> is built from:
<function>PQsendQuery</function> and <function>PQgetResult</function>.
<ItemizedList>
<ListItem>
<Para>
<Function>PQsendQuery</Function>
Submit a query to <ProductName>Postgres</ProductName> without
<itemizedlist>
<listitem>
<para>
<function>PQsendQuery</function>
Submit a query to <productname>Postgres</productname> without
waiting for the result(s). TRUE is returned if the query was
successfully dispatched, FALSE if not (in which case, use
PQerrorMessage to get more information about the failure).
......@@ -1173,12 +1197,12 @@ int PQsendQuery(PGconn *conn,
times to obtain the query results. <function>PQsendQuery</function> may not be called
again (on the same connection) until <function>PQgetResult</function> has returned NULL,
indicating that the query is done.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQgetResult</Function>
<listitem>
<para>
<function>PQgetResult</function>
Wait for the next result from a prior <function>PQsendQuery</function>,
and return it. NULL is returned when the query is complete
and there will be no more results.
......@@ -1193,13 +1217,13 @@ PGresult *PQgetResult(PGconn *conn);
Don't forget to free each result object with <function>PQclear</function> when done with it.
Note that <function>PQgetResult</function> will block only if a query is active and the
necessary response data has not yet been read by <function>PQconsumeInput</function>.
</Para>
</ListItem>
</para>
</listitem>
</ItemizedList>
</Para>
</itemizedlist>
</para>
<Para>
<para>
Using <function>PQsendQuery</function> and <function>PQgetResult</function>
solves one of <function>PQexec</function>'s problems:
If a query string contains multiple <acronym>SQL</acronym> commands, the results of those
......@@ -1211,10 +1235,10 @@ still cause the frontend to block until the backend completes the
next <acronym>SQL</acronym> command. This can be avoided by proper use of three more
functions:
<ItemizedList>
<ListItem>
<Para>
<Function>PQconsumeInput</Function>
<itemizedlist>
<listitem>
<para>
<function>PQconsumeInput</function>
If input is available from the backend, consume it.
<synopsis>
int PQconsumeInput(PGconn *conn);
......@@ -1226,20 +1250,20 @@ whether any input data was actually collected. After calling
<function>PQconsumeInput</function>, the application may check
<function>PQisBusy</function> and/or <function>PQnotifies</function> to see if
their state has changed.
</Para>
<Para>
</para>
<para>
<function>PQconsumeInput</function> may be called even if the application is not
prepared to deal with a result or notification just yet. The
routine will read available data and save it in a buffer, thereby
causing a <function>select</function>(2) read-ready indication to go away. The
application can thus use <function>PQconsumeInput</function> to clear the
<function>select</function> condition immediately, and then examine the results at leisure.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQisBusy</Function>
<listitem>
<para>
<function>PQisBusy</function>
Returns 1 if a query is busy, that is, <function>PQgetResult</function> would block
waiting for input. A 0 return indicates that <function>PQgetResult</function> can
be called with assurance of not blocking.
......@@ -1249,12 +1273,12 @@ int PQisBusy(PGconn *conn);
<function>PQisBusy</function> will not itself attempt to read data from the backend;
therefore <function>PQconsumeInput</function> must be invoked first, or the busy
state will never end.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQsocket</Function>
<listitem>
<para>
<function>PQsocket</function>
Obtain the file descriptor number for the backend connection socket.
A valid descriptor will be >= 0; a result of -1 indicates that
no backend connection is currently open.
......@@ -1268,13 +1292,13 @@ If the result of <function>select</function>(2) indicates that data can be read
the backend socket, then <function>PQconsumeInput</function> should be called to read the
data; after which, <function>PQisBusy</function>, <function>PQgetResult</function>,
and/or <function>PQnotifies</function> can be used to process the response.
</Para>
</ListItem>
</para>
</listitem>
</ItemizedList>
</Para>
</itemizedlist>
</para>
<Para>
<para>
A typical frontend using these functions will have a main loop that uses
<function>select</function>(2) to wait for all the conditions that it must
respond to. One of the conditions will be input available from the backend,
......@@ -1286,19 +1310,19 @@ When the main loop detects input ready, it should call
if <function>PQisBusy</function> returns false (0). It can also call
<function>PQnotifies</function> to detect NOTIFY messages (see "Asynchronous
Notification", below).
</Para>
</para>
<Para>
<para>
A frontend that uses <function>PQsendQuery</function>/<function>PQgetResult</function>
can also attempt to cancel a query that is still being processed by the backend.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Function>PQrequestCancel</Function>
Request that <ProductName>Postgres</ProductName> abandon
</para>
<para>
<itemizedlist>
<listitem>
<para>
<function>PQrequestCancel</function>
Request that <productname>Postgres</productname> abandon
processing of the current query.
<synopsis>
int PQrequestCancel(PGconn *conn);
......@@ -1313,17 +1337,17 @@ is effective, the current query will terminate early and return
an error result. If the cancellation fails (say, because the
backend was already done processing the query), then there will
be no visible result at all.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
Note that if the current query is part of a transaction, cancellation
will abort the whole transaction.
</Para>
</para>
<Para>
<para>
<function>PQrequestCancel</function> can safely be invoked from a signal handler.
So, it is also possible to use it in conjunction with plain
<function>PQexec</function>, if the decision to cancel can be made in a signal
......@@ -1332,22 +1356,22 @@ handler. For example, <application>psql</application> invokes
interactive cancellation of queries that it issues through <function>PQexec</function>.
Note that <function>PQrequestCancel</function> will have no effect if the connection
is not currently open or the backend is not currently processing a query.
</Para>
</para>
</Sect1>
</sect1>
<Sect1>
<Title>Fast Path</Title>
<sect1>
<title>Fast Path</title>
<Para>
<ProductName>PostgreSQL</ProductName> provides a fast path interface to send
<para>
<productname>PostgreSQL</productname> provides a fast path interface to send
function calls to the backend. This is a trapdoor into system internals and
can be a potential security hole. Most users will not need this feature.
<ItemizedList>
<ListItem>
<Para>
<Function>PQfn</Function>
<itemizedlist>
<listitem>
<para>
<function>PQfn</function>
Request execution of a backend function via the fast path interface.
<synopsis>
PGresult* PQfn(PGconn* conn,
......@@ -1385,18 +1409,18 @@ typedef struct {
should be checked before the result is used. The
caller is responsible for freeing the PGresult with
<function>PQclear</function> when it is no longer needed.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
</Sect1>
</sect1>
<Sect1>
<Title>Asynchronous Notification</Title>
<sect1>
<title>Asynchronous Notification</title>
<Para>
<ProductName>PostgreSQL</ProductName> supports asynchronous notification via the
<para>
<productname>PostgreSQL</productname> supports asynchronous notification via the
LISTEN and NOTIFY commands. A backend registers its interest in a particular
notification condition with the LISTEN command (and can stop listening
with the UNLISTEN command). All backends listening on a
......@@ -1406,17 +1430,17 @@ passed from the notifier to the listener. Thus, typically, any actual data
that needs to be communicated is transferred through a database relation.
Commonly the condition name is the same as the associated relation, but it is
not necessary for there to be any associated relation.
</Para>
</para>
<Para>
<FileName>libpq</FileName> applications submit LISTEN and UNLISTEN
<para>
<filename>libpq</filename> applications submit LISTEN and UNLISTEN
commands as ordinary SQL queries. Subsequently, arrival of NOTIFY
messages can be detected by calling PQnotifies().
<ItemizedList>
<ListItem>
<Para>
<Function>PQnotifies</Function>
<itemizedlist>
<listitem>
<para>
<function>PQnotifies</function>
Returns the next notification from a list of unhandled
notification messages received from the backend. Returns NULL if
there are no pending notifications. Once a notification is
......@@ -1433,33 +1457,33 @@ typedef struct pgNotify {
</synopsis>
After processing a PGnotify object returned by <function>PQnotifies</function>,
be sure to free it with <function>free()</function> to avoid a memory leak.
</Para>
<Note>
<Para>
</para>
<note>
<para>
In <productname>PostgreSQL</productname> 6.4 and later,
the <literal>be_pid</literal> is the notifying backend's,
whereas in earlier versions it was always your own backend's <acronym>PID</acronym>.
</Para>
</Note>
</ListItem>
</ItemizedList>
</Para>
</para>
</note>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
The second sample program gives an example of the use
of asynchronous notification.
</Para>
</para>
<Para>
<para>
<function>PQnotifies()</function> does not actually read backend data; it just
returns messages previously absorbed by another <application>libpq</application>
function. In prior releases of <Application>libpq</Application>, the only way
function. In prior releases of <application>libpq</application>, the only way
to ensure timely receipt of NOTIFY messages was to constantly submit queries,
even empty ones, and then check <function>PQnotifies()</function> after each
<function>PQexec()</function>. While this still works, it is
deprecated as a waste of processing power.
</Para>
<Para>
</para>
<para>
A better way to check for NOTIFY
messages when you have no useful queries to make is to call
<function>PQconsumeInput()</function>, then check <function>PQnotifies()</function>.
......@@ -1470,31 +1494,31 @@ to do. Note that this will work OK whether you use <function>PQsendQuery</funct
queries. You should, however, remember to check <function>PQnotifies()</function>
after each <function>PQgetResult</function> or <function>PQexec</function> to see
if any notifications came in during the processing of the query.
</Para>
</para>
</Sect1>
</sect1>
<Sect1>
<Title>Functions Associated with the COPY Command</Title>
<sect1>
<title>Functions Associated with the COPY Command</title>
<Para>
The COPY command in <ProductName>PostgreSQL</ProductName> has options to read from
or write to the network connection used by <FileName>libpq</FileName>.
<para>
The COPY command in <productname>PostgreSQL</productname> has options to read from
or write to the network connection used by <filename>libpq</filename>.
Therefore, functions are necessary to access this network
connection directly so applications may take advantage of this capability.
</Para>
</para>
<Para>
<para>
These functions should be executed only after obtaining a <literal>PGRES_COPY_OUT</literal>
or <literal>PGRES_COPY_IN</literal> result object from <function>PQexec</function>
or <function>PQgetResult</function>.
</Para>
</para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Function>PQgetline</Function>
<para>
<itemizedlist>
<listitem>
<para>
<function>PQgetline</function>
Reads a newline-terminated line of characters
(transmitted by the backend server) into a buffer
string of size length.
......@@ -1509,8 +1533,8 @@ the terminating newline into a null character.
<function>PQgetline</function> returns <literal>EOF</literal> at EOF, 0 if the
entire line has been read, and 1 if the buffer is full but the
terminating newline has not yet been read.
</Para>
<Para>
</para>
<para>
Notice that the application must check to see if a
new line consists of the two characters "\.",
which indicates that the backend server has finished sending
......@@ -1521,16 +1545,16 @@ care is needed to be sure one recognizes the "\." line correctly
(and does not, for example, mistake the end of a long data line
for a terminator line).
The code in
<FileName>
<filename>
src/bin/psql/copy.c
</FileName>
</filename>
contains example routines that correctly handle the copy protocol.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQgetlineAsync</Function>
<listitem>
<para>
<function>PQgetlineAsync</function>
Reads a newline-terminated line of characters
(transmitted by the backend server) into a buffer
without blocking.
......@@ -1552,8 +1576,8 @@ On each call, <function>PQgetlineAsync</function> will return data if a complete
terminated data line is available in libpq's input buffer, or if the
incoming data line is too long to fit in the buffer offered by the caller.
Otherwise, no data is returned until the rest of the line arrives.
</Para>
<Para>
</para>
<para>
The routine returns -1 if the end-of-copy-data marker has been recognized,
or 0 if no data is available, or a positive number giving the number of
bytes of data returned. If -1 is returned, the caller must next call
......@@ -1566,12 +1590,12 @@ last returned byte is <quote><literal>\n</literal></quote> or not.
The returned string is not null-terminated. (If you want to add a
terminating null, be sure to pass a bufsize one smaller than the room
actually available.)
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQputline</Function>
<listitem>
<para>
<function>PQputline</function>
Sends a null-terminated string to the backend server.
Returns 0 if OK, <literal>EOF</literal> if unable to send the string.
<synopsis>
......@@ -1581,12 +1605,12 @@ int PQputline(PGconn *conn,
Note the application must explicitly send the two
characters <quote><literal>\.</literal></quote> on a final line to indicate to
the backend that it has finished sending its data.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQputnbytes</Function>
<listitem>
<para>
<function>PQputnbytes</function>
Sends a non-null-terminated string to the backend server.
Returns 0 if OK, EOF if unable to send the string.
<synopsis>
......@@ -1597,12 +1621,12 @@ int PQputnbytes(PGconn *conn,
This is exactly like <function>PQputline</function>, except that the data buffer need
not be null-terminated since the number of bytes to send is
specified directly.
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQendcopy</Function>
<listitem>
<para>
<function>PQendcopy</function>
Syncs with the backend. This function waits until
the backend has finished the copy. It should
either be issued when the last string has been
......@@ -1617,12 +1641,12 @@ specified directly.
<synopsis>
int PQendcopy(PGconn *conn);
</synopsis>
</Para>
</para>
<Para>
<para>
As an example:
<ProgramListing>
<programlisting>
PQexec(conn, "create table foo (a int4, b char(16), d float8)");
PQexec(conn, "copy foo from stdin");
PQputline(conn, "3\thello world\t4.5\n");
......@@ -1630,13 +1654,13 @@ PQputline(conn,"4\tgoodbye world\t7.11\n");
...
PQputline(conn,"\\.\n");
PQendcopy(conn);
</ProgramListing>
</Para>
</ListItem>
</ItemizedList>
</Para>
</programlisting>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
When using <function>PQgetResult</function>, the application should respond to
a <literal>PGRES_COPY_OUT</literal> result by executing <function>PQgetline</function>
repeatedly, followed by <function>PQendcopy</function> after the terminator line is seen.
......@@ -1647,56 +1671,56 @@ result is processed by a series of <function>PQputline</function> calls followed
This arrangement will ensure that
a copy in or copy out command embedded in a series of <acronym>SQL</acronym> commands
will be executed correctly.
</Para>
<Para>
</para>
<para>
Older applications are likely to submit a copy in or copy out
via <function>PQexec</function> and assume that the transaction is done after
<function>PQendcopy</function>.
This will work correctly only if the copy in/out is the only
<acronym>SQL</acronym> command in the query string.
</Para>
</para>
</Sect1>
</sect1>
<Sect1>
<Title><Application>libpq</Application> Tracing Functions</Title>
<sect1>
<title><application>libpq</application> Tracing Functions</title>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Function>PQtrace</Function>
<para>
<itemizedlist>
<listitem>
<para>
<function>PQtrace</function>
Enable tracing of the frontend/backend communication to a debugging file stream.
<synopsis>
void PQtrace(PGconn *conn
FILE *debug_port)
</synopsis>
</Para>
</ListItem>
</para>
</listitem>
<ListItem>
<Para>
<Function>PQuntrace</Function>
<listitem>
<para>
<function>PQuntrace</function>
Disable tracing started by PQtrace
<synopsis>
void PQuntrace(PGconn *conn)
</synopsis>
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect1>
<Sect1>
<Title>
<Application>libpq</Application> Control Functions</Title>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Function>PQsetNoticeProcessor</Function>
</para>
</listitem>
</itemizedlist>
</para>
</sect1>
<sect1>
<title>
<application>libpq</application> Control Functions</title>
<para>
<itemizedlist>
<listitem>
<para>
<function>PQsetNoticeProcessor</function>
Control reporting of notice and warning messages generated by libpq.
<synopsis>
typedef void (*PQnoticeProcessor) (void *arg, const char *message);
......@@ -1706,13 +1730,13 @@ PQsetNoticeProcessor(PGconn *conn,
PQnoticeProcessor proc,
void *arg);
</synopsis>
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
By default, <Application>libpq</Application> prints <quote>notice</quote> messages
<para>
By default, <application>libpq</application> prints <quote>notice</quote> messages
from the backend as well as a few error messages that it generates by itself
on <filename>stderr</filename>.
This behavior can be overridden by supplying a callback function that
......@@ -1721,169 +1745,169 @@ the text of the error message (which includes a trailing newline), plus
a void pointer that is the same one passed to <function>PQsetNoticeProcessor</function>.
(This pointer can be used to access application-specific state if needed.)
The default notice processor is simply
<ProgramListing>
<programlisting>
static void
defaultNoticeProcessor(void * arg, const char * message)
{
fprintf(stderr, "%s", message);
}
</ProgramListing>
</programlisting>
To use a special notice processor, call <function>PQsetNoticeProcessor</function> just after
creation of a new PGconn object.
</Para>
</para>
<Para>
<para>
The return value is the pointer to the previous notice processor. If you supply a callback
function pointer of NULL, no action is taken, but the current pointer is returned.
</Para>
</para>
</Sect1>
</sect1>
<Sect1 id="libpq-envars">
<Title>Environment Variables</Title>
<sect1 id="libpq-envars">
<title>Environment Variables</title>
<Para>
<para>
The following environment variables can be used to select default
connection parameter values, which will be used by <function>PQconnectdb</function> or
<function>PQsetdbLogin</function> if no value is directly specified by the calling code.
These are useful to avoid hard-coding database names into simple
application programs.
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
<envar>PGHOST</envar> sets the default server name.
If a non-zero-length string is specified, TCP/IP communication is used.
Without a host name, libpq will connect using a local Unix domain socket.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGPORT</envar> sets the default port or local Unix domain socket
file extension for communicating with the <ProductName>PostgreSQL</ProductName>
file extension for communicating with the <productname>PostgreSQL</productname>
backend.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGDATABASE</envar> sets the default
<ProductName>PostgreSQL</ProductName> database name.
</Para>
</ListItem>
<ListItem>
<Para>
<productname>PostgreSQL</productname> database name.
</para>
</listitem>
<listitem>
<para>
<envar>PGUSER</envar>
sets the username used to connect to the database and for authentication.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGPASSWORD</envar>
sets the password used if the backend demands password authentication.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGREALM</envar> sets the Kerberos realm to use with
<ProductName>PostgreSQL</ProductName>, if it is different from the local realm.
If <envar>PGREALM</envar> is set, <ProductName>PostgreSQL</ProductName>
<productname>PostgreSQL</productname>, if it is different from the local realm.
If <envar>PGREALM</envar> is set, <productname>PostgreSQL</productname>
applications will attempt authentication with servers for this realm and use
separate ticket files to avoid conflicts with local
ticket files. This environment variable is only
used if Kerberos authentication is selected by the backend.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGOPTIONS</envar> sets additional runtime options for
the <ProductName>PostgreSQL</ProductName> backend.
</Para>
</ListItem>
<ListItem>
<Para>
the <productname>PostgreSQL</productname> backend.
</para>
</listitem>
<listitem>
<para>
<envar>PGTTY</envar> sets the file or tty on which debugging
messages from the backend server are displayed.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
The following environment variables can be used to specify user-level default
behavior for every Postgres session:
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
<envar>PGDATESTYLE</envar>
sets the default style of date/time representation.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGTZ</envar>
sets the default time zone.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
The following environment variables can be used to specify default internal
behavior for every Postgres session:
<ItemizedList>
<ListItem>
<Para>
<itemizedlist>
<listitem>
<para>
<envar>PGGEQO</envar>
sets the default mode for the genetic optimizer.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGRPLANS</envar>
sets the default mode to allow or disable right-sided plans in the optimizer.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGCOSTHEAP</envar>
sets the default cost for heap searches for the optimizer.
</Para>
</ListItem>
<ListItem>
<Para>
</para>
</listitem>
<listitem>
<para>
<envar>PGCOSTINDEX</envar>
sets the default cost for indexed searches for the optimizer.
</Para>
</ListItem>
</ItemizedList>
</Para>
</para>
</listitem>
</itemizedlist>
</para>
<Para>
<para>
Refer to the <command>SET</command> <acronym>SQL</acronym> command
for information on correct values for these environment variables.
</Para>
</para>
</Sect1>
</sect1>
<Sect1>
<Title>Caveats</Title>
<sect1>
<title>Caveats</title>
<Para>
<para>
The query buffer is 8192 bytes long, and queries over
that length will be rejected.
</Para>
</Sect1>
</para>
</sect1>
<Sect1>
<Title>Sample Programs</Title>
<sect1>
<title>Sample Programs</title>
<Sect2>
<Title>Sample Program 1</Title>
<sect2>
<title>Sample Program 1</title>
<Para>
<ProgramListing>
<para>
<programlisting>
/*
* testlibpq.c Test the C version of Libpq, the Postgres frontend
* library.
......@@ -2008,15 +2032,15 @@ main()
/* fclose(debug); */
}
</ProgramListing>
</Para>
</Sect2>
</programlisting>
</para>
</sect2>
<Sect2>
<Title>Sample Program 2</Title>
<sect2>
<title>Sample Program 2</title>
<Para>
<ProgramListing>
<para>
<programlisting>
/*
* testlibpq2.c
* Test of the asynchronous notification interface
......@@ -2129,15 +2153,15 @@ main()
PQfinish(conn);
}
</ProgramListing>
</Para>
</Sect2>
</programlisting>
</para>
</sect2>
<Sect2>
<Title>Sample Program 3</Title>
<sect2>
<title>Sample Program 3</title>
<Para>
<ProgramListing>
<para>
<programlisting>
/*
* testlibpq3.c Test the C version of Libpq, the Postgres frontend
* library. tests the binary cursor interface
......@@ -2311,9 +2335,26 @@ main()
PQfinish(conn);
}
</ProgramListing>
</Para>
</Sect2>
</Sect1>
</Chapter>
</programlisting>
</para>
</sect2>
</sect1>
</chapter>
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