After the fork occured recently my geth 1.5 client process blocks too slowly is it another DDos attack? if not how to deal with this problem
a similar question was posted today on reddit: https://www.reddit.com/r/ethereum/comments/5egco7/is_there_a_new_dos_attack_im_running_geth_152_and/
the answer comes from Vitalik, indicating that this is the result of the state clearing process :
This is the state clearing process working as intended. It looks like a DoS, because it's "poking" about 20 million accounts by zero-value calling each one, and each call causes the protocol to notice that the account is empty and thereby delete it from the state. The process of deleting the account from the state takes O(log(n)) disk writes, but the zero-value call only costs 700 gas, and so it these transactions take longer than usual to process.
Note that any state clearing mechanism that we could have implemented would still have required making these 20 million account deletions, so this is unfortunately an unavoidable temporary side effect; we can dial down the speed of the process if users find the current level too difficult to deal with, though that will increase the length of time the spam will have to go on.
The only way to do it is to poke empty accounts, and once all ~20 million empty accounts have been poked it will no longer be possible to do this; all modifications to the account tree will cost at least 5700 gas per modification.