IBM 000-8697 Manual Do Utilizador

System Architecture

The minimum value of

DBSPACES

 is 1, representing the root dbspace.

The latch table is not a table in the same sense as other tables, but it functions
in a similar manner to track all latches in the OnLine system. Refer to

for a detailed discussion of how OnLine uses latches to control and

manage modifications to OnLine shared memory.

The number of latch entries is equal to the number of shared-memory
resources configured for the OnLine system. As OnLine administrator, you
cannot modify the number of latches.

You can obtain information about latches from the tbstat -s output. You can
use the user process information from the tbstat -u output to determine if a
user process is holding a latch.

The lock table represents the pool of available locks. Each entry in the lock
table represents one lock. A single transaction can own multiple locks. A
single user process is limited to 32 concurrent table locks. The lock table
includes an associated hash table.

When an entry in the lock table is used, a lock is created. The information
stored in the table describes the lock. The lock description includes the
following four items:

■

The address of the user process that owns the lock

■

The type of lock (exclusive, update, shared, byte, or intent)

■

The page and/or rowid that is locked

■

The tblspace where the lock is placed

The number of entries in the lock table is equal to the maximum number of
locks in this OnLine system, specified as

LOCKS

in the configuration file. Each

entry in the lock table occupies 32 bytes.

Refer to

utorial for an explanation of locking and

SQL

 statements. Refer to

 for a detailed explanation of the effect of

locks on buffer management. Refer to

 for information on

monitoring locks with tbstat -k.