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[5.3] Added database slave failover #15553

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merged 5 commits into from
Nov 2, 2016
Merged

[5.3] Added database slave failover #15553

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4a839cf
Added database slave failover to laravel framework
Data33 Sep 21, 2016
9f8dfee
Replaced tabs with spaces
Data33 Sep 22, 2016
ae4b2f9
Fixed a couple of code style issues
Data33 Sep 22, 2016
bd9acdf
Added empty comment and sorted imports by length
Data33 Sep 22, 2016
c9125f3
PDOException is now handled by ExceptionHandler
Data33 Sep 23, 2016
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59 changes: 53 additions & 6 deletions src/Illuminate/Database/Connectors/ConnectionFactory.php
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
namespace Illuminate\Database\Connectors;

use PDO;
use PDOException;
use Illuminate\Support\Arr;
use InvalidArgumentException;
use Illuminate\Database\MySqlConnection;
Expand Down Expand Up @@ -95,6 +96,58 @@ protected function createReadPdo(array $config)
* @return \Closure
*/
protected function createPdoResolver(array $config)
{
if (array_key_exists('host', $config)) {
return $this->createPdoResolverWithHosts($config);
}

return $this->createPdoResolverWithoutHosts($config);
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@taylorotwell taylorotwell Oct 13, 2016 •
edited
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Why would a database configuration ever not have a host property?

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As far as I could see, sqlite configurations don't have a host property, hence the two different methods.

}

/**
* Create a new Closure that resolves to a PDO instance with a specific host or an array of hosts.
*
* @param array $config
* @return \Closure
*/
protected function createPdoResolverWithHosts(array $config)
{
return function () use ($config) {
if (! is_array($config['host'])) {
$hosts = [$config['host']];
} else {
$hosts = $config['host'];
shuffle($hosts);
}

$lastHost = end($hosts);
foreach ($hosts as $host) {
$config['host'] = $host;

try {
return $this->createConnector($config)->connect($config);
} catch (PDOException $e) {
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Would this suppress any other exceptions? Such as the user not having access to the database or the database not existing? If so I'd think we would want to be much more narrow in scope and report all but the actual connection error.

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I guess it could suppress other exceptions.
Letting the exception bubble up would kind of defeat the purpose of having a failover.
Would logging connection errors be enough, or do we need to actually show the user why a specific host could not be connected to?

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Exceptions definitely need to bubble up to at lease the handler so we can report them to things like sentry. Otherwise your primary db could be failing and you would have no idea.

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That's an excellent point.
I'll edit the PR first thing tomorrow morning to fix that

if ($host !== $lastHost) {
$this->container->make('Illuminate\Contracts\Debug\ExceptionHandler')->report($e);
}
}
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An empty comment should be added.

} catch(PDOException $e) {
    //
}

}

if (empty($hosts)) {
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Why not making this check before the foreach loop.

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If I move the check above the foreach loop it will be tested even if a connection was actually made, which seems redundant to me
It really is mostly a check so $e actually exists, since it's created inside the foreach loop

throw new InvalidArgumentException('Database hosts array cannot be empty');
}

throw $e;
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What are you throwing here? You're not even in a try catch block.

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The only way for the code to reach that throw statement is if all hosts have failed. If so, the $e variable will be set from the catch block in the last iteration of the foreach loop.
If any host succeeded, the method would have returned already.

};
}

/**
* Create a new Closure that resolves to a PDO instance where there is no configured host.
*
* @param array $config
* @return \Closure
*/
protected function createPdoResolverWithoutHosts(array $config)
{
return function () use ($config) {
return $this->createConnector($config)->connect($config);
Expand All @@ -111,12 +164,6 @@ protected function getReadConfig(array $config)
{
$readConfig = $this->getReadWriteConfig($config, 'read');

if (isset($readConfig['host']) && is_array($readConfig['host'])) {
$readConfig['host'] = count($readConfig['host']) > 1
? $readConfig['host'][array_rand($readConfig['host'])]
: $readConfig['host'][0];
}

return $this->mergeReadWriteConfig($config, $readConfig);
}

Expand Down