CodeIgniter：MSSQL Server 2008 R2上发生数据库错误

Question

I am connecting to MS SQL Server 2008 R2 and my php version is 5.3 and I use PHP Codeigniter 1.7.2. It was already running on live and there is a lot of members using it. But after days of deployment I always experiencing error:

A Database Error Occurred
Unable to connect to your database server using the provided settings.

Sometimes it's work properly but when the time that many members accessing it then the error is suddenly occurred. I need to restart the server in order the site works properly.

Here is my Database.php config

$active_group = "default";
$active_record = TRUE;

$db['default']['hostname'] = 'liveserver\server08r2'; 
$db['default']['username'] = 'xxx';
$db['default']['password'] = 'xxxxx';
$db['default']['database'] = 'DATABASE_NAME';
$db['default']['dbdriver'] = 'mssql';
$db['default']['dbprefix'] = '';
$db['default']['pconnect'] = TRUE;
$db['default']['db_debug'] = FALSE;
$db['default']['cache_on'] = FALSE;
$db['default']['cachedir'] = "";
$db['default']['char_set'] = "utf8";
$db['default']['dbcollat'] = "utf8_general_ci";

Can be a factor that the error occurred when many people using the site? Do I need to adjust something in my code in order not to experience this problem again? What would be the possible problem on this issue.

My Error Logs are here. Maybe these can help to solve the issue.

ERROR - 2013-08-23 11:44:07 --> Severity: Warning  --> mssql_select_db() [<a href='function.mssql-select-db'>function.mssql-select-db</a>]: Unable to select database:  [PROJECT_DATABASE] C:\xampp\htdocs\project\system\database\drivers\mssql\mssql_driver.php 112
ERROR - 2013-08-23 11:44:07 --> Unable to select database: PROJECT_DATABASE
ERROR - 2013-08-23 14:15:54 --> Severity: Warning  --> mssql_query() [<a href='function.mssql-query'>function.mssql-query</a>]: Query failed C:\xampp\htdocs\project\system\database\drivers\mssql\mssql_driver.php 143
ERROR - 2013-08-23 14:15:54 --> Severity: Warning  --> mssql_query() [<a href='function.mssql-query'>function.mssql-query</a>]: message: The ROLLBACK TRANSACTION request has no corresponding BEGIN TRANSACTION. (severity 16) C:\xampp\htdocs\project\system\database\drivers\mssql\mssql_driver.php 143
ERROR - 2013-08-23 14:15:54 --> Severity: Warning  --> mssql_query() [<a href='function.mssql-query'>function.mssql-query</a>]: Query failed C:\xampp\htdocs\project\system\database\drivers\mssql\mssql_driver.php 143
ERROR - 2013-08-23 15:44:07 --> Severity: Warning  --> mssql_select_db() [<a href='function.mssql-select-db'>function.mssql-select-db</a>]: Unable to select database:  [PROJECT_DATABASE] C:\xampp\htdocs\project\system\database\drivers\mssql\mssql_driver.php 112
ERROR - 2013-08-23 15:44:07 --> Unable to select database: PROJECT_DATABASE

Answer 1

This has happened to me a few times. In my case, PHP server failed to resolve SQL server address at random. I would suggest hard coding the IP address of 'liveserver\\server08r2' in your Windows hosts file (%windir%\\system32\\drivers\\etc\\hosts) on your PHP server.

In addition, change $db['default']['pconnect'] to false in your CodeIgniter config file.

Answer 2

a small list of things that I check (after checking the logs) when I have such errors in production and development/testing.

1. Check if there is enough disk space on the application partition. Make sure you have ENOUGH free space (not only 10-20MB).
2. Check if MSSQL (or MySQL) have any limit on open connections.
3. CPU/Ram? Maybe you are out of RAM on your shared hosting/VPS or whatever you are using?

Answer 3

My guess:

Your CI application has nothing to do with the issue. More than probably is your DDBB, and it's because of the peak of people using the site: The more people using the site, the more SQL you have to run, so your DDBB is saying "that was enough!" and rejecting the queries. When you restart the server, your issue dissapears because as you've cleaned the queries queue, now is free to keep launching queries.

For checking it and been totally sure, log the long time queries, and, if I'm right, it will appear a lot of them when the issue starts: http://dev.mysql.com/doc/refman/5.1/en/slow-query-log.html

That will give you a clue about where your bottle necks are, and if you optimize your long time queries, the server will be able of resolve more queries in less time, aka more users in your system without the issue appearing.

Anyway, if your application user number is growing up, you'll have to move to a bigger system hiring/buying a bigger server, or changing your infrastructure to the cloud: Amazon web services or Google APP Engine.

Answer 4

Change

$db['default']['pconnect'] = TRUE;

to

$db['default']['pconnect'] = FALSE;

Then restart your webserver.

EDIT:

Given that the problem occurs at rush time which means many connections to the database which leads to issuing many queries, then my best guess is; you're database is experiencing deadlocks or blocking, really can't judge since I'm not aware of how your SQL Server error log looks like.

What I can judge on, based on the information you've provided, is that it's definitely SQL Server issue.

Run the following query to check if there are any deadlocks on resources that you use in your application:

SELECT  L.request_session_id AS SPID, 
    DB_NAME(L.resource_database_id) AS DatabaseName,
    O.Name AS LockedObjectName, 
    P.object_id AS LockedObjectId, 
    L.resource_type AS LockedResource, 
    L.request_mode AS LockType,
    ST.text AS SqlStatementText,        
    ES.login_name AS LoginName,
    ES.host_name AS HostName,
    TST.is_user_transaction as IsUserTransaction,
    AT.name as TransactionName,
    CN.auth_scheme as AuthenticationMethod
FROM    sys.dm_tran_locks L
    JOIN sys.partitions P ON P.hobt_id = L.resource_associated_entity_id
    JOIN sys.objects O ON O.object_id = P.object_id
    JOIN sys.dm_exec_sessions ES ON ES.session_id = L.request_session_id
    JOIN sys.dm_tran_session_transactions TST ON ES.session_id = TST.session_id
    JOIN sys.dm_tran_active_transactions AT ON TST.transaction_id = AT.transaction_id
    JOIN sys.dm_exec_connections CN ON CN.session_id = ES.session_id
    CROSS APPLY sys.dm_exec_sql_text(CN.most_recent_sql_handle) AS ST
WHERE   resource_database_id = db_id()
ORDER BY L.request_session_id

If the query returns results on queries (used in your application), then you are on the right path and you may want to try to optimize the target query, drop recreate indexes, etc.. There are some useful information in SO or MSDN that can help you to resolve deadlocks or/and blocking.

Answer 5

This error occurred because you may not have enabled php mssql extension in php.ini. Please try once enabling mssql extension.