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    <p>Maybe late, but this may benefit someone searching on the same question.</p> <p>The underlying implementation is a simple 32 bit binary counter, which is incremented every 100th of a second, starting from when the database was last started.</p> <p>This binary counter is is being mapped onto a PL/SQL BINARY_INTEGER type - which is a signed 32-bit integer (there is no sign of it being changed to 64-bit on 64-bit machines).</p> <p>So, presuming the clock starts at zero it will hit the +ve integer limit after about 248 days, and then flip over to become a -ve value falling back down to zero.</p> <p>The good news is that provided both numbers are the same sign, you can do a simple subtraction to find duration - otherwise you can use the 32-bit remainder.</p> <pre><code> IF SIGN(:now) = SIGN(:then) THEN RETURN :now - :then; ELSE RETURN MOD(:now - :then + POWER(2,32),POWER(2,32)); END IF; </code></pre> <p>Edit : This code will blow the int limit and fail if the gap between the times is too large (248 days) but you shouldn't be using GET_TIME to compare durations measure in days anyway (see below).</p> <p>Lastly - there's the question of why you would ever use GET_TIME.</p> <p>Historically, it was the only way to get a sub-second time, but since the introduction of SYSTIMESTAMP, the only reason you would ever use GET_TIME is because it's fast - it is a simple mapping of a 32-bit counter, with no real type conversion, and doesn't make any hit on the underlying OS clock functions (SYSTIMESTAMP seems to).</p> <p>As it only measures relative time, it's only use is for measuring the duration between two points. For any task that takes a significant amount of time (you know, over 1/1000th of a second or so) the cost of using a timestamp instead is insignificant.</p> <p>The number of occasions on where it is actually useful is minimal (the only one I've found is checking the age of data in a cache, where doing a clock hit for every access becomes significant).</p>
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