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ReadOnly(mapping=None, *, ignore_unknown_fields=False, **kwargs)
Message type to initiate a read-only transaction.
Attributes | |
---|---|
Name | Description |
strong |
bool
Read at a timestamp where all previously committed transactions are visible. |
min_read_timestamp |
Executes all reads at a timestamp >= min_read_timestamp .
This is useful for requesting fresher data than some
previous read, or data that is fresh enough to observe the
effects of some previously committed transaction whose
timestamp is known.
Note that this option can only be used in single-use
transactions.
A timestamp in RFC3339 UTC "Zulu" format, accurate to
nanoseconds. Example: "2014-10-02T15:01:23.045123456Z" .
|
max_staleness |
Read data at a timestamp >= NOW - max_staleness seconds.
Guarantees that all writes that have committed more than the
specified number of seconds ago are visible. Because Cloud
Spanner chooses the exact timestamp, this mode works even if
the client's local clock is substantially skewed from Cloud
Spanner commit timestamps.
Useful for reading the freshest data available at a nearby
replica, while bounding the possible staleness if the local
replica has fallen behind.
Note that this option can only be used in single-use
transactions.
|
read_timestamp |
Executes all reads at the given timestamp. Unlike other modes, reads at a specific timestamp are repeatable; the same read at the same timestamp always returns the same data. If the timestamp is in the future, the read will block until the specified timestamp, modulo the read's deadline. Useful for large scale consistent reads such as mapreduces, or for coordinating many reads against a consistent snapshot of the data. A timestamp in RFC3339 UTC "Zulu" format, accurate to nanoseconds. Example: "2014-10-02T15:01:23.045123456Z" .
|
exact_staleness |
Executes all reads at a timestamp that is exact_staleness old. The timestamp is chosen soon after
the read is started.
Guarantees that all writes that have committed more than the
specified number of seconds ago are visible. Because Cloud
Spanner chooses the exact timestamp, this mode works even if
the client's local clock is substantially skewed from Cloud
Spanner commit timestamps.
Useful for reading at nearby replicas without the
distributed timestamp negotiation overhead of
max_staleness .
|
return_read_timestamp |
bool
If true, the Cloud Spanner-selected read timestamp is included in the Transaction][google.spanner.v1.Transaction]
message that describes the transaction.
|