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Fig. 9.1
Lock-compatibility
matrix for multi-granular
locking with the lock modes
S, X, IS, IX, SIX
Fig. 9.2
Lock-upgrade
matrix for multi-granular
locking with the lock modes
S, X, IS, IX, SIX
Fig. 9.3
The lattice of the
multi-granular lock modes S,
X, IS, IX, SIX
There is no ordering relation between the lock modes IX and S. Their supremum
(smallest common upper bound) in the lattice is SIX.
Example 9.2
The following two scenarios are possible in the multi-granular locking
protocol (Fig.
9.4
a, b):
(a) Transaction T
1
holds an IS lock on relation r andanSlockonthekeyx of a
tuple in r . At the same time, another transaction T
2
holds an IX lock on r ,an
Slockonx, and an X lock on another key y that is also present in r . In addition,
a third transaction T
3
holds an IX lock on r and an X lock on a third key
z
that
also exists in r .
(b) Transactions T
1
and T
2
hold IS locks on relation r and S locks on a key x in r .
At the same time, transaction T
3
holds a SIX lock on r and an X lock on another
key y that is also present in r .
The following scenario is not possible (Fig.
9.4
c):
(c) Transaction T
1
holds an IX lock on relation r andanXlockonkeyx in r .At
the same time T
2
holds a SIX lock on r .
