The Codeless Code: Case 131 Don't Think 
======

 A new monk of Elephant's Footprint Clan noticed that all
brothers under master Bawan’s tutelage answered questions
promptly, without the slightest pause. Those who hesitated
were given a swift rap on the head with the master’s staff,
after which they were to remain silent for the rest of the
day—assuming, of course, that they had not been knocked
unconscious by the blow.

The young monk asked one of the brothers, “Why does Bawan
punish those who delay in their answers?”

“Because he believes them to be thinking,” said the elder
monk. He indicated a row of skulls set on a ledge above the
master’s door. Some were dull and dusty while others
appeared to be freshly-parted from their previous owners,
but carved into the forehead of each were the words DON’T
THINK in the master’s unmistakable script.

The elder monk departed, leaving the younger to ponder
Bawan’s algorithm.

Some time later these same two monks were working furiously
through the night to upgrade one of the clan’s venerable
document databases. Critical systems were offlined while the
old documents were migrated to the new servers.

The conversion script ran for hours, yet failed near the end
due to a minor problem. A second run was started, but since
dawn was fast approaching the monks specified that any
documents which had already been written by the first run
should be skipped.

As the second run sped through the portion of the database
that the first already processed, Bawan noticed something
curious.  Many thousands of status messages scrolled past
which looked like this:

document 2677091: skipped (already exists) document 2677092:
skipped (already exists) document 2677093: skipped (already
exists)

Yet once in a while one would appear which looked like this:

document 2677094: skipped (already exists) (** source is
newer)

“Why the difference?” demanded Bawan.

“I cannot say,” said the elder monk quickly. Bawan snorted
and struck the man’s cheek with the back of his hand. Then
he turned to the younger monk.

“Why the difference?” he repeated.

In that instant—his mind racing between thoughts of the
master’s hand and the master’s staff—the young monk received
a flash of insight.

“Clock skew,” declared the young monk. “When we pull a
source document from the old server we preserve its
modification time, and then we create the target document.
Yet if the system clocks disagree, the script will sometimes
believe that the source is newer than the target.”

The master indeed found a small time discrepancy between the
two servers. He nodded approvingly and departed, leaving the
young monk to bask in the satisfaction of having understood
Bawan’s algorithm.

One day later Bawan ordered the clan to assemble outside his
office. As all waited for the master to appear, the elder
monk whispered that Bawan had spent the whole day assembling
definitive evidence that clock skew was responsible for the
odd messages.

“What did he find?” asked a nun.

“Nothing of the sort,” said the elder monk. “In truth, one
server had accidentally been left running during the
migration, so users were still making edits in the old
database. The second conversion skipped these documents with
the observed warning.  When traffic was diverted to the new
database, subsequent user edits made restoration of the lost
edits impossible. It will be a great embarrassment for the
clan.”

The discussion halted abruptly as Bawan emerged from his
office with a ladder, which he then ascended to place a
glistening new skull on the ledge above his door. The
skull’s features recalled those of the young monk, who had
not been seen all day.  As before, the words DON’T THINK
were inscribed on the forehead. And on the jawbone—invisible
to anyone standing below the ledge but quite legible as the
master carried it up—was the single word, KNOW.