#870 √ resolved
Anthony

Issues with DboSource::$methodCache

Reported by Anthony | June 28th, 2010 @ 10:55 PM | in 1.3.2

We are using Cake 1.3 final and have been trying to get to the bottom of a bug in our app for weeks. There is a script in which we do hundreds of thousands of queries, and every so often, completely nonsensical WHERE condition strings show up in a query - ones that seem like they belong in a different query. This is despite the fact that our logic uses the correct conditions in Model::find().

Finally, we were able to trace it back to the $methodCache in DboSource. As it turns out, the DboSource analyzes the conditions, generates a hash key using crc32(), and sets the value equal to the processed condition string. If new conditions match the hash, it outputs the processed condition string, rather than rebuilding it from scratch. The problem is, crc32() isn't always unique, and for scripts with many queries, collisions are possible, as evidenced in our app.

Now, I realize this can potentially be classified as a feature, seeing as how crc32() is fast, and there is a way to manually disable method caching if you desire. However, I don't believe it's documented, and this potential issue isn't really explained in any capacity.

So I propose 1 of 2 solutions:
1. The documentation should warn developers about this potential pitfall
2. The code should be updated to use a hashing method that's guaranteed unique, and thus avoid the issue in the first place

Comments and changes to this ticket

  • Mark Story

    Mark Story June 29th, 2010 @ 05:07 PM

    • → Tag set to “dbosource, documentation, methodcache”
    • → Assigned user set to “Mark Story”
    • → Milestone set to “1.3.2”

    I think documentation is a good approach. Fully unique hashes can be slower than crc32 which is why it was chosen. Disabling the cache when its not helpful and providing good documentation on how to do that is probably more pertinent.

  • CakePHP

    CakePHP June 30th, 2010 @ 07:53 AM

    • → State changed from “new” to “resolved”
  • johnnymoped

    johnnymoped August 21st, 2010 @ 04:39 PM

    Sorry for hijacking this bugreport, but I ran into the same problem and couldn't find help anywhere.
    Is there a way to disable the methodCache (setting $cacheMethods to false) from within a cake shell?
    I tried the following (on cake 1.3.3), but without success:

    class MyShell extends Shell
    {

    var $uses = array(....);

function initialize()
{
    App::import("Core","ConnectionManager");
    $db =&ConnectionManager::getDataSource('local');
    $db->cacheMethods = false;
    parent::initialize();
}

function main()
{
    ....
}
  • ADmad

    ADmad August 21st, 2010 @ 04:51 PM

    Well this is still a bug tracker not a help forum. Post your question on cakeqs.org or cake-php google group.

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