As alleged, this was a due to a family clan feud over a political dynasty. I am not going to go into specifics about what happened and why; there is plenty already on the news and news sites. What I am going to discuss is the safety in Davao.
The massacre occurred in southern region of Maguindanao, which is located in the ARMM, Autonomous Region in Muslim Mindanao. This is an area of Mindanao comprised mostly of peoples of the Muslim faith. This region has for years wanted self-rule and has had many instances of terror.
How does this affect Davao, actually, except for grief and sorrow for the people who lost their lives, and something to follow in the news, not much. Davao is a safe city run by Mayor Duterte. He is very strong against political wars and crime.
When something happens, or threats occur, he tightens security in the city. I have seen checkpoints set up at different locations manned by Army members who stop all vehicles and inspect the contents if felt necessary.
At times during the year where there are more than normal amounts of people at certain locations, check points are again set up since terrorists like to target these locations. The beginning on November, during All Souls and All Saints Day, the police and Army checkpoints were set up near the cemeteries. At Easter and Christmas times, there will be Army presence at the malls.
Is any place in this world safe? Of course not, but the added security and presence of the Army and their checkpoints help keep Davao a safe location for Foreigners and Filipinos to live.