Both of these phenomena tend to cause government spending to go up.
Pork barrel spending is spending on specific projects that are to be be carried out in specific areas of the country. They are generally given out to the various representatives so that those people can brag about the amount of government spending they have gotten for their districts. Logrolling is the trading of votes where Representative A votes for Representative B's bill and Representative B reciprocates. By making these deals, the representatives vote for each other's spending bills and help to pass bills that create more government spending.
Pork barrel legislation and logrolling, then, encourage more and more government spending because all legislators have incentive to vote for spending and no one has much incentive to vote against it.