When you create a Material, the Material IDs are not in sequence.
For Example: From 1500000 to 1500022, material IDs are in sequence. But afterwards number range for materials is not in sequence.
For performance reasons the drawing of numbers for products is buffered, i.e. when a new number is requested, 10 numbers are determined and reserved immediately. This helps to speed up mass creation of products significantly, but it has the side effect that after some time the reserved numbers in the buffer are invalidated and thus not used in scenarios where for a longer period no new numbers are needed.
So, in a productive scenario where usually lots of new products are created within the system within a short time, you barely notice any "missing" numbers while you profit from the performance improvement.
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