I have written numerous times about pension problems in the US. Let's cross the Atlantic and take a peek at the setup in Spain, then let's compare the two setups.
Via translation from Libre Mercado, please consider The Chart That Will Shake Future Pensioners.
Workers vs. Pensioners
Given that eight million people age 65 and 16.7 million workers cannot sustain the current pension, imagine what will happen in the coming decades as the differential goes back even closer.
Pensions today promise Social Security payments of 100% of the average wage in the last 25 years for those with 37 years of Social Security contributions. Such payments are absolutely unsustainable. The relative income of pensioners relative to the average income of the society will sink (without massive tax looting of active workers).
Immigration could partially alleviate the problem, making the demographic transition somewhat smoother, but if new rights accrue to future pensions, immigration only delays the problem. In any case, it might be a good idea to allow free immigration to Spain in exchange for not accrue rights to Social Security.
The most important practical advice to draw from the above chart is simple: save and invest. If you trust your retirement to politicians, you will end up poor and feeling cheated.