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MDL-51245 sqlsrv: Diagnose missing READ_COMMITTED_SNAPSHOT mode

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Without it, transactions are executed in standard READ_COMMITED
mode, without snapshoting/row versioning, leading to update
conflicts under high concurrency.
This commit is contained in:
Eloy Lafuente (stronk7) 2015-09-04 03:00:52 +02:00
parent a9daab4927
commit 48657a6713
1 changed files with 31 additions and 0 deletions
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31
lib/dml/sqlsrv_native_moodle_database.php
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@ -117,6 +117,37 @@ class sqlsrv_native_moodle_database extends moodle_database {
return get_string('nativesqlsrvhelp', 'install');
}
/**
* Diagnose database and tables, this function is used
* to verify database and driver settings, db engine types, etc.
*
* @return string null means everything ok, string means problem found.
*/
public function diagnose() {
// Verify the database is running with READ_COMMITTED_SNAPSHOT enabled.
// (that's required to get snapshots/row versioning on READ_COMMITED mode).
$correctrcsmode = false;
$sql = "SELECT is_read_committed_snapshot_on
FROM sys.databases
WHERE name = '{$this->dbname}'";
$this->query_start($sql, null, SQL_QUERY_AUX);
$result = sqlsrv_query($this->sqlsrv, $sql);
$this->query_end($result);
if ($result) {
if ($row = sqlsrv_fetch_array($result)) {
$correctrcsmode = (bool)reset($row);
}
}
$this->free_result($result);
if (!$correctrcsmode) {
return get_string('mssqlrcsmodemissing', 'error');
}
// Arrived here, all right.
return null;
}
/**
* Connect to db
* Must be called before most other methods. (you can call methods that return connection configuration parameters)