ReadLockMode(value)ReadLockMode is used to set the read lock mode for read-write
transactions.
- If isolation level is
`REPEATABLE_READ][google.spanner.v1.TransactionOptions.IsolationLevel.REPEATABLE_READ]`,
then it is an error to specify `read_lock_mode`. Locking
semantics default to `OPTIMISTIC`. No validation checks
are done for reads, except to validate that the data that
was served at the snapshot time is unchanged at commit
time in the following cases:
1. reads done as part of queries that use
`SELECT FOR UPDATE`
2. reads done as part of statements with a
`LOCK_SCANNED_RANGES` hint
3. reads done as part of DML statements
- At all other isolation levels, if `read_lock_mode` is
the default value, then pessimistic read locks are used.
PESSIMISTIC (1):
Pessimistic lock mode.
Read locks are acquired immediately on read. Semantics
described only applies to
`SERIALIZABLE][google.spanner.v1.TransactionOptions.IsolationLevel.SERIALIZABLE]`
isolation.
OPTIMISTIC (2):
Optimistic lock mode.
Locks for reads within the transaction are not acquired on
read. Instead the locks are acquired on a commit to validate
that read/queried data has not changed since the transaction
started. Semantics described only applies to
`SERIALIZABLE][google.spanner.v1.TransactionOptions.IsolationLevel.SERIALIZABLE]`
isolation.
Enum |
|
|---|---|
| Name | Description |
READ_LOCK_MODE_UNSPECIFIED |
Default value. |