(PHP 4, PHP 5, PHP 7, PHP 8)
pg_pconnect — Abre uma conexão PostgreSQL persistente
pg_pconnect() abre uma conexão com um banco de dados PostgreSQL. Ele retorna uma instância PgSql\Connection que é necessária para outras funções do PostgreSQL.
Se uma segunda chamada for feita para pg_pconnect() com
o mesmo connection_string de uma conexão existente, a
conexão existente será retornada a menos que você passe
PGSQL_CONNECT_FORCE_NEW como
flags.
Para ativar a conexão persistente, a diretiva pgsql.allow_persistent no php.ini deve ser definida como "On" (que é o padrão). O número máximo de conexões persistentes pode ser definido com a diretiva pgsql.max_persistent no php.ini (o padrão é -1 para nenhum limite). O número total de conexões pode ser definido com a diretiva pgsql.max_links no php.ini.
pg_close() não irá fechar conexões persistentes geradas por pg_pconnect().
connection_string
O connection_string pode estar vazio para usar todos os parâmetros padrão ou
pode conter uma ou mais configurações de parâmetro separadas por espaços em branco.
Cada configuração de parâmetro está no formato palavra-chave = valor. Os espaços ao redor
do sinal de igual são opcionais. Para escrever um valor vazio ou
contendo espaços, coloque-o entre aspas simples, por exemplo, palavra-chave =
'um valor'. Aspas simples e barras invertidas dentro do valor devem ser
escapadas com uma barra invertida, ou seja, \' e \\.
As palavras-chave de parâmetro atualmente reconhecidas são:
host, hostaddr, port,
dbname, user,
password, connect_timeout,
options, tty (ignorada), sslmode,
requiressl (descontinuada em favor de sslmode), e
service. Quais desses argumentos existem depende
da sua versão do PostgreSQL.
flags
Se PGSQL_CONNECT_FORCE_NEW for passado, então uma nova conexão
será criada, mesmo que connection_string seja idêntico a
uma conexão existente.
Retorna uma instância PgSql\Connection em caso de sucesso, ou false em caso de falha.
| Versão | Descrição |
|---|---|
| 8.1.0 | Retorna uma instância PgSql\Connection agora; anteriormente, um resource era retornado. |
Exemplo #1 Usando pg_pconnect()
<?php
$dbconn = pg_pconnect("dbname=mary");
//conecta a um banco de dados chamado "mary"
$dbconn2 = pg_pconnect("host=localhost port=5432 dbname=mary");
//conecta a um banco de dados chamado "mary" em "localhost" na porta "5432"
$dbconn3 = pg_pconnect("host=sheep port=5432 dbname=mary user=lamb password=foo");
//conecta a um banco de dados chamado "mary" no host "sheep" com usuário e senha
$conn_string = "host=sheep port=5432 dbname=test user=lamb password=bar";
$dbconn4 = pg_pconnect($conn_string);
//conecta a um banco de dados chamado "test" no host "sheep" com usuário e senha
?>As of Aug 2007, some suggestions from the postgresql forums
on pg_pconnect(), faster postgres connections, and connection pooling:
Summary:
http://archives.postgresql.org/pgsql-general/2007-08/msg01406.php
Good details: http://archives.postgresql.org/pgsql-general/2007-08/msg00660.php
Also: http://archives.postgresql.org/pgsql-general/2007-08/msg01489.phpYou should not use pg_pconnect - it's broken. It will work but it doesn't really pool, and it's behaviour is unpredictable. It will only make you rise the max_connections parameter in postgresql.conf file until you run out of resources (which will slow your database down).
If you have many concurrent connections to your database, you should use the PostgreSQL connection pooler PgBouncer (developed by the Skype-team). When using pgbouncer, make sure you use pg_connect and NOT pg_pconnect. Also, make sure you close your connections with pg_close.
* PGBouncer homepage:
http://developer.skype.com/SkypeGarage/DbProjects/PgBouncer
* PostgreSQL pooling article by Last.fm:
http://www.last.fm/user/Russ/journal/2008/02/21
/zd_postgres_connection_pools:_pgpool_vs._pgbouncerInstead of reducing MaxClients in apache you may try to
reduce pgsql.max_links in php to at least the number of
postmasters. It should work and leave
you with more available httpds for static html pages.If a transaction is in progress when page processing ends, is it aborted before the connection placed bak in the pool? Or is the connection added "as is"?
It would seem that the correct thing to do is to always 'ABORT' before adding to the pool.
As a note, this would be a good time to check and see if the connection is still open before readding it. Thus allowing closed connections to be cleaned up over time, instead of hanging around for ever as they do now.<?php
//
// Using pg_pconnect in a class.
//
// Why this? Because the manual says:
//
// If a second call is made to pg_pconnect() with the same
// connection_string as an existing connection, the existing
// connection will be returned unless you pass
// PGSQL_CONNECT_FORCE_NEW as connect_type.
//
// This is not always true.
//
/**
* MyClassA creates a postgresql connection using pg_pconnect
* and stores the resulting resource id to $this->conn
*/
class MyClassA
{
function __construct($connection_string)
{
$this->conn =
pg_pconnect($connection_string)
or die('Wrong CONN_STRING');
}
}
//
// Showing current php.ini settings to be sure
// that persistent connections s are allowed.
// -1 means 'unlimited'
//
echo '<br>pgsql.allow_persistent: ' . ini_get('pgsql.allow_persistent');
echo '<br>pgsql.max_persistent: ' . ini_get('pgsql.max_persistent');
echo '<br>pgsql.max_links: ' . ini_get('pgsql.max_links');
echo '<br><br>';
// setting one custom connection string for all objects
// (modify $connection_string to fit your needs)
$connection_string =
'host=localhost port=5432' .
' dbname=test user=test password=test';
//
// Creating 10 MyClassA objects using the same $connection_string
//
$objArr = Array();
for ($i = 0; $i < 10; $i++)
{
$objArr[] = new MyClassA($connection_string);
}
//
// Human readable result:
//
foreach($objArr as $id => $object)
{
printf(
'%s: Object %s: using db %s<br>',
get_class($object), $id, $object->conn
);
}
/* ------------------------------------------------------------- */
// The result
// pgsql.allow_persistent: 1
// pgsql.max_persistent: -1
// pgsql.max_links: -1
//
// MyClassA: Object 0: using db Resource id #2
// MyClassA: Object 1: using db Resource id #3
// MyClassA: Object 2: using db Resource id #4
// MyClassA: Object 3: using db Resource id #5
// MyClassA: Object 4: using db Resource id #6
// MyClassA: Object 5: using db Resource id #7
// MyClassA: Object 6: using db Resource id #8
// MyClassA: Object 7: using db Resource id #9
// MyClassA: Object 8: using db Resource id #10
// MyClassA: Object 9: using db Resource id #11
//
/* ------------------------------------------------------------- */
//
// Each MyClassA object will use its _own_ database Resource id
//
?>Be careful when using Apache/PHP dynamic module/PostgreSQL :
in httpd.conf (Apache conf) default MaxClients is 150, whereas default PG's max_connections is 32 which is much fewer than 150. You have to set max_connections to at least MaxClients (and pg's shared_buffers to 2*max_connections at least) to avoid PG's errors with pg_pconnect like : "Sorry, too many clients already connected"To setup a high availability server with apache as a static module and postgreSQL, change httpd.conf and set MaxClients to less than max postgreSQL simultaneous connections (like 32 or 64).
This way pg_pconnect will allways return a valid handle under heavy traffic or under a request flow attack without wasting resources and without connection problems.