Be careful when utilizing mssql_pconnect to connect to multiple databases on the same server using different credentials. For example:
/* first connection */
$conn1 = mssql_pconnect('production-server','sa','1234');
$row = mssql_query('select top 10 * from invoices', $conn1);
/* open another connection, same server different */
$conn2 = mssql_pconnect('production-server','loweruser','6789');
Results in the error:
PHP Warning: mssql_select_db(): Unable to select database: someotherdb
I suspect mssql_pconnect detects a connect opened to "production-server" and just re-uses it, regardless of whether or not the credentials are the same. We did not notice this until consolidating two different MSSQL servers onto one server with two databases with different users/permissions. Reverting back to mssql_connect() solves the problem.
(PHP 4, PHP 5, PECL odbtp >= 1.1.1)
mssql_pconnect — Open persistent MS SQL connection
$new_link= false ]]]] )
mssql_pconnect() acts very much like mssql_connect() with two major differences.
First, when connecting, the function would first try to find a (persistent) link that's already open with the same host, username and password. If one is found, an identifier for it will be returned instead of opening a new connection.
Second, the connection to the SQL server will not be closed when the execution of the script ends. Instead, the link will remain open for future use ( mssql_close() will not close links established by mssql_pconnect()).
This type of links is therefore called 'persistent'.
The MS SQL server. It can also include a port number. e.g. hostname:port.
If a second call is made to mssql_pconnect() with the same arguments, no new link will be established, but instead, the link identifier of the already opened link will be returned. This parameter modifies this behavior and makes mssql_pconnect() always open a new link, even if mssql_pconnect() was called before with the same parameters.
Returns a positive MS SQL persistent link identifier on success, or
FALSE on error.
Example #1 mssql_pconnect() using the
// Connect to MSSQL and select the database
$link1 = mssql_pconnect('MANGO\SQLEXPRESS', 'sa', 'phpfi');
// Create a new link
$link2 = mssql_pconnect('MANGO\SQLEXPRESS', 'sa', 'phpfi', true);
Be careful with pconnect!
Platform: RH Linux 7.3, PHP 4.2.1. FreeTDS.
pconnect does give you better time than connect (about 0.25-0.4 seconds gain) BUT:
- occasionally, I've experienced "quirks" when fetch() would randomly return empty recordsets from stored procedurest that can_not return empty recordsets by definition.
- if you restart MSSQL server while some of the connections did not time out, next pconnect() will not establish a new connection! It will return an old one, so next time you do execute() or query() your script will just _hang_ until timeouted by Apache.
All of the above I believe are FreeTDS problems, not PHP. I wonder if somebody with PHP+Sybase lib got pconnect to work.
Please note that mssql_pconnect creates a connection for the pool for *each process*. If you have "ThreadsPerChild" set to 50 in apache, and mssql.max_procs set to 25 in php, then eventually you will get mssql_pconnect failing to give you a connection to the database. This has stumped me for quite a while, and the answer finally presented itself thanks to the people in #php.
If you are running PHP/Apache combination on a Windows machine that is part of a domain, using NT Authentication to connect to a MS SQL Server, you must to do the following things:
1) Turn NT Authentication On (under MSSQL in php.ini)
2) Configure the Apache service to run as the user that is authorized to access the MS SQL server.
Hope this helps save someone the time that it took me to track down!