I recently performed a MySQL upgrade on Windows Server 2008R2.

I moved from MySQL 5.1 to MySQL 5.6.22 (Community Edition).

(NOTE: PHP is currently 5.3.0)

Things went just fine for all my WordPress installs (no problems on cutover); however, all my Drupal 7 sites are now generating 500 errors (coming from php-cgi.exe via php5ts.dll from what I can tell).

To address concerns about the broad nature of the question, this is the specific Windows Event Log message:

    Faulting application name: php-cgi.exe, version: 5.3.0.0, time stamp: 0x4a492a25
    Faulting module name: php5ts.dll, version: 5.3.0.0, time stamp: 0x4a4929bb
    Exception code: 0xc0000005
    Fault offset: 0x0015e1b0
    Faulting process id: 0x7bb4
    Faulting application start time: 0x01d01fa8dec6e9a6
    Faulting application path: C:\PHP\php-cgi.exe
    Faulting module path: C:\PHP\php5ts.dll
    Report Id: 2e661541-8b9c-11e4-a303-001b210e0a6a

I've checked database credentials, time zone defaults, and haven't changed IIS settings, folder permissions, or anything of that nature.

The one difference that stands out, is that Drupal uses PDO for access, and I'm wondering if there is a potential issue there (re: versions ... since all these sites worked fine under MySQL 5.1).

PDO seems to be showing version 5.0.5-dev (rev 1.3.2.27).

I can't locate anything that leads to identification, troubleshooting or resolution.

(I'm off to try to replicate with just a simple PDO test.)

Has anybody encountered this and/or have documentation that might help isolate/resolve things?

NOTE: The closest I've come is to somebody using PDO drivers for MSSQL (not MySQL) where there was a faulty Drupal layer on top of PDO. Details here - http://forums.iis.net/t/1181446.aspx?PHP+5+3+8+Problems

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UPDATE:

Not PDO...

The following example (with real values) works fine.

    $dsn = 'mysql:host=localhost;dbname=DBNAME';
    $username = 'USER';
    $password = 'PASS';
    $options = array();
    
    $dbh = new PDO($dsn, $username, $password, $options);
    
    if ($dbh) {
    
    	$stmt = $dbh->query('SELECT * FROM MYTABLE LIMIT 1');
    	$results = $stmt->fetchAll(PDO::FETCH_ASSOC);
    
    	print_r($results);
    
    }
    else {
    	echo 'Failed.';
    }

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UPDATE 2:

I have double checked any options set by the prior install of MySQL 5.1 that might not have been carried over. I realize more things are auto-set and defaults might have changed, which could be part of the issue.

The other issue that might come into play is changing the server collation default from **utf8** to **utf8mb4** ... It looks like Drupal 7 should support this (discussion, in the framework of Drupal 8 goes back to 2011 - https://www.drupal.org/node/1314214)