The logged error is not very useful without more context...
Also spotted for [POST LAYERGROUP ERROR].
Tried locally by killing redis or sql-api but in both cases the error that comes out is still nicely prefixes.
I suspect the error comes deep from the tryGetTileOrGrid, and specifically from torque renderer, not prefixing the error raised by the sql adapter here: https://github.com/CartoDB/Windshaft/blob/0.19.1/lib/windshaft/renderers/torque.js#L376
On our side (windshaft-cartodb) we could prefix the error where we catch it (during layers test, I suppose)
ERR, that's still done in windshaft, so nothing for us here, all delegated to CartoDB/Windshaft#164
Upgrade windshaft to 0.19.2
Fixes obscure "ECONNREFUSED" error message (closes #171)
Change some http status responses to be more appropriate to the case