Sift flour with soda and salt and set aside. In a large bowl, cream butter until light. Gradually beat in sugar. Add eggs and vanilla and continue beating until light and fluffy. Gradually blend in dry ingredients. Add pecans and mix well. Turn dough out onto lightly floured surface. Divide into 4 equal parts. Shape each into a roll about 10 inches long. Wrap in plastic wrap and refrigerate until firm about 8 hours. Slice dough 1/8 inch thick; place 2 inches apart on ungreased cookie sheet and bake at 375 degrees F for 7-10 minutes.