Types of Lock Modes
There are four types of lock modes in the SAP System:
1.
S (Shared)
mode for shared lock.
2.
E (Exclusive)
mode for exclusive locks.
3.
X (eXclusive
non-cumulative) mode for exclusive but not cumulative locks
4.
(Optimistic) mode for optimistic lock
Shared
lock uses S (Shared) mode – where several
users (transactions) can access locked data at the same time in display mode. A
request for another shared lock is accepted, even if it comes from another
user. An exclusive lock set on an object that already has a shared lock will be
rejected.
Exclusive
lock uses E (Exclusive) mode – where an exclusive
lock protects the locked object against all types of locks from other
transactions. Only the same lock owner can reset the lock (accumulate).
Exclusive locks can be requested several times from the same transaction and
are processed successively.
Exclusive
but not cumulative lock uses X (eXclusive non-cumulative) mode – where
in contrast to Exclusive locks, exclusive but not cumulative locks can be
called only once from the same transaction. Each further lock request will be
rejected.
Optimistic
lock uses (Optimistic)
mode – where optimistic locks initially behave
like shared locks and can be converted into exclusive locks.
Shared
lock uses S (Shared) mode – where several
users (transactions) can access locked data at the same time in display mode. A
request for another shared lock is accepted, even if it comes from another
user. An exclusive lock set on an object that already has a shared lock will be
rejected.
Exclusive
lock uses E (Exclusive) mode – where an exclusive
lock protects the locked object against all types of locks from other
transactions. Only the same lock owner can reset the lock (accumulate).
Exclusive locks can be requested several times from the same transaction and
are processed successively.
Exclusive
but not cumulative lock uses X (eXclusive non-cumulative) mode – where
in contrast to Exclusive locks, exclusive but not cumulative locks can be
called only once from the same transaction. Each further lock request will be
rejected.
Optimistic
lock uses (Optimistic)
mode – where optimistic locks initially behave
like shared locks and can be converted into exclusive locks.
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