I got my invite for hackday today.
Anyone else coming?
CakePHP’s invisible query cache
I just wanted to document something that was driving me nuts in Cake PHP.
I do a simple find on a model:
$thing = $this->Model->find(array('id' => 123), NULL, NULL, 1);
Then later on, I make the same query again. Only the first query appears in the SQL debug output. Why call it again? Well, I’ve made some manual queries in between the calls using SQL that is inconvenient to emulate in Cake functions, in particular INSERT IGNORE. It turns out that Cake has a largely undocumented query cache, but Cake has no idea that its cache is dirty because of the manual queries. The _clearCache function is not yet implemented for the query cache, so the only choice is to disable it before the first query, and you can do that during a single instantiation by saying:
$this->Model->cacheQueries = false;
Note that the query has 1 level of recursion, which means that all the sub-queries are also cached. Setting cacheQueries to false on this one model means that all queries through it don’t get cached, including those that may be in other models via relationships.
Who’s the Daddy?
3Ware RAID rebuilding
I’ve had the dubious honour of seeing some RAID failures and rebuilds lately. It’s the kind of thing that doesn’t get written about in the manuals very well, in particular what your RAID will report when it’s having trouble. So, here are a couple of examples from a 3Ware RAID controller using tw_cli software. This is what tw_cli /c4 show displays when we have a dead drive:
Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 RAID-1 DEGRADED - - - 149.05 ON - Port Status Unit Size Blocks Serial --------------------------------------------------------------- p0 OK u0 149.05 GB 312581808 G2109NHG p1 DEGRADED u0 149.05 GB 312581808 G20X1BWG
So, we swap the drive, and it looks like this while rebuilding:
Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 RAID-1 REBUILDING 89 - - 149.05 ON - Port Status Unit Size Blocks Serial --------------------------------------------------------------- p0 OK u0 149.05 GB 312581808 G2109NHG p1 DEGRADED u0 149.05 GB 312581808 G209Y0HG
and after a little while…
Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 RAID-1 OK - - - 149.05 ON - Port Status Unit Size Blocks Serial --------------------------------------------------------------- p0 OK u0 149.05 GB 312581808 G2109NHG p1 OK u0 149.05 GB 312581808 G209Y0HG
There are plenty of obvious strings to match in this output (though there are many other reports available), so it’s a reasonable thing to base a monitoring script on.
It’s nice to see it actually work, and makes me extremely grateful that I bothered getting RAID n the first place. This would be a much unhappier post if I hadn’t.