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pg_pconnect持続的な PostgreSQL 接続をオープンする


pg_pconnect(string $connection_string, int $connect_type = ?): resource

pg_pconnect() は PostgreSQL への接続を オープンします。この関数は、他の PostgreSQL関数 が必要とする 接続リソースを返します。

既存の接続と同じ connection_string を用いて pg_pconnect() が 2 回目にコールされた場合は、 既存の接続を返します。ただし、connect_typePGSQL_CONNECT_FORCE_NEW を指定している場合は 除きます。

持続的接続を有効にするには、php.ini のディレクティブ pgsql.allow_persistent を "On" に設定する必要があります(デフォルトは On です)。 持続的接続の最大数は php.ini ディレクティブ pgsql.max_persistent で設定可能です(デフォルトは制限無しを意味する -1 です)。 接続全体の数は php.ini ディレクティブ pgsql.max_links で設定可能です。

pg_close() は、 pg_pconnect() によりオープンされた持続的接続は 閉じません。



すべてデフォルトのパラメータを使用する場合には connection_string を空にすることが可能です。 または 1 つ以上のパラメータを空白で区切って指定することも可能です。 個々のパラメータは keyword = value の形式で 設定します。等号の前後の空白はあってもなくてもかまいません。 空の値や空白を含む値を指定する場合は、その値をシングルクォートで 囲みます(例: keyword = 'a value')。値の中に シングルクォートやバックスラッシュが含まれる場合は、それらを バックスラッシュでエスケープする必要があります(例: \' および \\)。

現在利用できるパラメータは以下のとおりです。 host, hostaddr, port, dbname, user, password, connect_timeout, options, tty(無視されます), sslmode, requiressl(非推奨。代わりに sslmode を推奨します) および service 。これらのうち実際にどの パラメータが使えるかは、PostgreSQL のバージョンに依存します。


PGSQL_CONNECT_FORCE_NEW が渡された場合は、 たとえ connection_string が既存の接続と まったく同一であっても新しい接続をオープンします。


成功した場合に PostgreSQL の接続リソース、失敗した場合に false を返します。

例1 pg_pconnect() の使用法

// "mary"という名前のデータベースに接続

$dbconn2 pg_pconnect("host=localhost port=5432 dbname=mary");
// "localhost"のポート"5432"にて"mary"という名前のデータベースに接続

$dbconn3 pg_pconnect("host=sheep port=5432 dbname=mary user=lamb password=foo");
// ユーザー名とパスワードを指定してホスト"sheep"上の"mary"という名前のデータベースに接続

$conn_string "host=sheep port=5432 dbname=test user=lamb password=bar";
$dbconn4 pg_pconnect($conn_string);
// ユーザー名とパスワードを指定してホスト"sheep"上の"test"という名前のデータベースへ接続


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User Contributed Notes 10 notes

12 years ago
You 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:

* PostgreSQL pooling article by
Dennis Fogg
13 years ago
As of Aug 2007, some suggestions from the postgresql forums
on pg_pconnect(), faster postgres connections, and connection pooling:


Good details:
info at karl-philipp dot de
17 years ago
A contribution to the transaction issue raised by "garrett at bgb dot cc".

In a German book about PostgreSQL in connection with PHP (Cornelia Boenigk, PostgreSQL - Grundlagen, Praxis, Anwendungsentwicklung mit PHP) one can read in chapter 19.3 about persistent connections:
If the page processing aborts and the transaction is not finished yet, the next script using the same persistent connection will be considered as the continuation of the transaction. In particular a lock of a table will persist. The explanation is as follows: After the abort of the script no COMMIT or ROLLBACK was sent to the db server.

The author describes a hint to avoid the scenario above:
You can create a function for resolving transactions and locks erroneously not closed. For invoking the function after execution of a script it has to be registered with the function register_shutdown_function():
herve at elma dot fr
20 years ago
For resetting an apache web server and in same time the persistent connections you may use :
./apachectl graceful
dmitri at graphictype dot com
21 years ago
How to reset persistent connections:

killall -USR1 httpd
garrett at bgb dot cc
19 years ago
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.
Spiros Ioannou
18 years ago
Instead 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.
raggaflo at libertysurf dot fr
19 years ago
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"
etsysx dot i dot hate dot spam at teleline dot es
19 years ago
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.
ts at dev dot websafe dot pl
13 years ago
// 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
$this->conn =
                or die(

// 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');
'<br>pgsql.max_persistent: ' . ini_get('pgsql.max_persistent');
'<br>pgsql.max_links: ' . ini_get('pgsql.max_links');

// 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 => $object)
'%s: Object %s: using db %s<br>',
get_class($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
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