When defining the IDENTITY column for the books table, we used the default numeric value of (18, 0), which provides a total of 999,999,999,999,999,999 ID numbers. For the identity burning set factor configuration parameter, we are using the default setting of 5000 (.05 percent of 999,999,999,999,999,999), which means that Adaptive Server allocates blocks of 500,000,000,000,000 numbers.
The server allocates the first 500,000,000,000,000 numbers in memory and stores the highest number of the block (500,000,000,000,000) on the table’s OAM page. When all the numbers are assigned to rows or burned, the server takes the next block of numbers (the next 500,000,000,000,000), starting with 500,000,000,000,001, and stores the number 1,000,000,000,000,000 as the highest number of the block.
Let’s say, after row number 500,000,000,000,022 the server fails. Only numbers 1 through 500,000,000,000,022 were used as ID numbers for books. Numbers 500,000,000,000,023 through 1,000,000,000,000,000 are burned. When the server is running again, it creates ID numbers starting from the highest number stored on the table’s OAM page plus one (1,000,000,000,000,001),which leaves a gap of 499,999,999,999,978 ID numbers.
To reduce this large gap in identity numbers for a specific table, you can set the identity gap as described in “Example of using identity_gap.”
