Short answers, pulled from the story.
The exchange system broke down in mid-1863 when the Confederacy refused to treat black prisoners as equal to white prisoners. Before that collapse, most prisoners were swapped relatively quickly between 1861 and 1863.
About 56,000 soldiers died in prisons during the war accounting for almost 10% of all Civil War fatalities. Camp Sumter near Andersonville Georgia saw 13,000 of the 45,000 Union soldiers confined there die over a period of 14 months.
Andersonville located near Andersonville Georgia became the deadliest prison in the Civil War where 13,000 of the 45,000 Union soldiers imprisoned there died. A larger prison called Camp Lawton was constructed near Lawton Depot in Millen Georgia in summer 1864 to relieve conditions at Andersonville.
Henry Wirz served as commander at Andersonville and was executed for war crimes following postwar legal proceedings. The trial examined documents including Captain Henry Wirz's official records and reports from Harper's Weekly published between 1863 and 1864.
On the 11th of December 1861, Congress passed a joint resolution calling on President Lincoln to inaugurate systematic measures for prisoner exchange. This action followed public opinion changes after the First Battle of Bull Run when over one thousand Union soldiers were captured by Confederates.