Jim Gray, 63, the noted database researcher, veteran of stints at IBM, Tandem Computers, and most recently Microsoft, is missing at sea. He set out Sunday morning to do something that I have done twice, sail from San Francisco's Golden Gate Bridge across 27 miles of ocean to the Farallon Islands. He hasn't returned.I once did a long interview with Jim Gray on parallel processing and database operation. Relational databases presented a good opportunity to take advantage of parallel processing, he said, and patiently explained how both the SQL query and the access of records in the database itself could be broken down into parallel functions.

He had a teacher's patience with my questions. We talked for over an hour until I felt the subject was exhausted, or at least the limits of my understanding had been exhausted. But I felt he was willing to continue and dive deeper, if I had been so inclined. I was grateful for such open sharing of knowledge.

Now the Coast Guard's helicopter, its C-130 search plane, two 87-foot patrol boats, a 41-foot Coast Guard utility boat, and an Alameda County maritime patrol boat are searching 1,750 square miles of ocean for him. That's not very reassuring.

The route to the Farallons is a straightforward one. It follows the commercial shipping channel, marked by buoys on each side, for about half the distance. As you reach the area where the container ships and other commercial vessels take on their San Francisco Bay pilots to guide them through the Golden Gate, you have another 13 to 14 nautical miles to traverse, but as you leave the San Francisco shoreline behind, there's only a brief interlude of an hour or two of open water before the Farallon Islands appear in front of you. They're on a compass heading similar to the shipping channel's path. By regulation, sailboats carry VHF radios, life preservers, fire extinguishers, flare signals, all the simple lifesaving gear that will get you out of many of the extremities you might stumble into. Near the Farallon Islands, it's possible a radio distress call wouldn't reach back to land, but there are almost always ships within the radio's 22 to 23 mile range to pick up the signal. No such signal was reported from any quarter.

Experienced sailors are asking, did the one calamity that can befall a single-handed sailing vessel occur? That is, did the skipper fall overboard and his boat sail away from him before he could get a hold on it? Single-handers typically wear a harness that keeps them linked to the boat, even if pitched overboard. Besides, where's the boat, we're asking?

The weather was clear, the winds were light, the waves 4-feet to 5-feet high, according to weather reports. With Gray's 40-foot boat, Tenacious, these conditions should not have presented a big challenge. My boat, the 25-foot Calypso Poet, took the waves at 6 feet to 7 feet without incident on previous expeditions and an acquaintance has shown several times you can get there and back in a 22-foot Cal.

I hope Jim Gray will yet be found in some unexpected quarter. The rudder jammed and he ended up far off course. Perhaps Tenacious developed a leak that overwhelmed the bilge pump, and he's astride the hull somewhere, waiting to be picked up. Sailboat hulls float, even when waterlogged. But the water is cold. Experienced sailors are worried about Jim Gray.