
2-40 IBM Informix OnLine Database Server Administrator’s Guide
Managing Shared-Memory Resources
Considerwhathappenswhentwo OnLineserverprocessesattemptto attach
to shared memory simultaneously. Both server processes attempt to access
thenextavailable slot intheuser table. OnLinerequirestechniques 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
Figure 2-5
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
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