Database Reference
In-Depth Information
data consistency at all. Readers would read the current (modified) version of the row regardless of what happens next,
if changes would be rolled back, or if a row is modified multiple times. We can see that behavior in Figure
17-5
.
Figure 17-5.
Read uncommitted and shared lock behavior
In read committed transaction isolation level readers acquire and release shared (S) locks immediately. This
prevents readers from accessing uncommitted data modified by other sessions (shared (S) locks are incompatible
with exclusive (X) locks). We can see this behavior in Figure
17-6
.
Figure 17-6.
Read committed and shared lock behavior