Shared-Memory Lower-Boundary Address

When the database server attaches shared-memory segments subsequent to the first segment, it assumes that the segment can be attached contiguous with the previous one; that is, that a segment can be attached at the address of the previous segment plus the size of that segment. However, your operating system might set a parameter that defines a lower-boundary address for attaching shared-memory segments. If the size of a segment would cause it to cross the lower-boundary address, the segment is attached at a point beyond the end of the previous segment, creating a gap between shared-memory segments. For an illustration of this situation, refer to How Virtual Processors Attach to Shared Memory.