Indicates how to choose the timestamp at which to read the data for Cloud Spanner read-only transactions.
If your application can tolerate some staleness when reading data, you can use a stale read,
which can execute much faster when compared to reading the latest data.
Executes all reads at a timestamp that is duration
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 MaxStaleness.
MaxStaleness
Read data at a timestamp >= NOW - duration. 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.
MinReadTimestamp
Executes all reads at a timestamp >= minReadTimestamp.
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.
ReadTimestamp
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.
Strong
Read at a timestamp where all previously committed transactions
are visible.
