2-40 IBM Informix OnLine Database Server Administrator’s Guide
Managing Shared-Memory Resources
Considerwhat happens when two OnLine server processes attempt to attach
to shared memory simultaneously. Both server processes attempt to access
thenext available slot in the user table. OnLine requires techniques by which
it can control concurrent access to individual shared-memory resources.
OnLine employs four mechanisms as part of shared-memory resource
management:
■Buffer locks
■Latches
■Timestamps
■Hash tables
Figure2-5
Components of
shared
memory. The
shared-
memory header
contains
pointers to all other
shared-
memory
structures.
Shared-
memory header User table
Lock table
Hash table
Dbspace table
Transaction table
Latch table
Tblspace table
Hash table
Buffer header table
Hash table
Chunk table
Page-cleaner table
Buffer pool