Huck Keys anxiously surveys the floor of the Harvard Square HMV Records, looking for customers who may need assistance and for managers who may be scrutinizing his performance.

It's a Friday night, exactly two weeks before Christmas Eve, and Keys, a 27-year-old Somerville resident in Pumas and slim gray cords, hasn't been working at HMV a week.

The same weekend, across the river at Boston's Prudential Center, Ed Savage lets forth a hearty chuckle as he sits easily on top of his sleigh, decked out a furry red and white Santa Claus costume. A tot riding by in a stroller waves and laughs when Santa waves back.

The solidly built Savage, 54, is clearly enjoying the respite from his day job as a postal worker in his seventh year as the Prudential Center Santa.

With his Santa-like physique and festive clothing, Savage in his sleigh seems worlds apart from the nervous Keys, but they're filling similar slots this holiday season.

With a public intent on efficient holiday shopping, the demand for short-term holiday workers like these two is particularly high this year.

As the Dow continues to rise and unemployment figures fall to record lows, a tight labor market challenges retail store managers who need extra staff to maximize profits from holiday shoppers.

"It's extremely difficult to find help [right now]," says Gerald Olbach, the president of the Cambridge Chamber of Commerce.