Snapshot API

Model a set of read-only queries to a database as a snapshot.

class google.cloud.spanner_v1.snapshot.Snapshot(session, read_timestamp=None, min_read_timestamp=None, max_staleness=None, exact_staleness=None, multi_use=False)

Allow a set of reads / SQL statements with shared staleness.

See https://cloud.google.com/spanner/reference/rpc/google.spanner.v1#google.spanner.v1.TransactionOptions.ReadOnly

If no options are passed, reads will use the strong model, reading at a timestamp where all previously committed transactions are visible.

  • Parameters

    • session (Session) – The session used to perform the commit.

    • read_timestamp (datetime.datetime) – Execute all reads at the given timestamp.

    • min_read_timestamp (datetime.datetime) – Execute all reads at a timestamp >= min_read_timestamp.

    • max_staleness (datetime.timedelta) – Read data at a timestamp >= NOW - max_staleness seconds.

    • exact_staleness (datetime.timedelta) – Execute all reads at a timestamp that is exact_staleness old.

    • multi_use (bool) – If true, multiple read() / execute_sql() calls can be performed with the snapshot in the context of a read-only transaction, used to ensure isolation / consistency. Incompatible with max_staleness and min_read_timestamp.

begin()

Begin a read-only transaction on the database.

  • Return type

    bytes

  • Returns

    the ID for the newly-begun transaction.

  • Raises

    ValueError – if the transaction is already begun, committed, or rolled back.

execute_sql(sql, params=None, param_types=None, query_mode=None, query_options=None, request_options=None, partition=None, retry=<_MethodDefault._DEFAULT_VALUE:

Perform an ExecuteStreamingSql API request.

  • Parameters

    • sql (str) – SQL query statement

    • params (dict, **{str -> column value}) – values for parameter replacement. Keys must match the names used in sql.

    • param_types (dict[str -> Union[dict, *[types.Type](spanner_v1/types.md#google.cloud.spanner_v1.types.Type)]*]) – (Optional) maps explicit types for one or more param values; required if parameters are passed.

    • query_mode (QueryMode) – Mode governing return of results / query plan. See: QueryMode.

    • query_options – (Optional) Query optimizer configuration to use for the given query. If a dict is provided, it must be of the same form as the protobuf message QueryOptions

    • request_options (google.cloud.spanner_v1.types.RequestOptions) – (Optional) Common options for this request. If a dict is provided, it must be of the same form as the protobuf message RequestOptions.

    • partition (bytes) – (Optional) one of the partition tokens returned from partition_query().

    • retry (Retry) – (Optional) The retry settings for this request.

    • timeout (float) – (Optional) The timeout for this request.

  • Return type

    StreamedResultSet

  • Returns

    a result set instance which can be used to consume rows.

  • Raises

    ValueError – for reuse of single-use snapshots, or if a transaction ID is already pending for multiple-use snapshots.

partition_query(sql, params=None, param_types=None, partition_size_bytes=None, max_partitions=None, *, retry=<_MethodDefault._DEFAULT_VALUE:

Perform a PartitionQuery API request.

  • Parameters

    • sql (str) – SQL query statement

    • params (dict, **{str -> column value}) – values for parameter replacement. Keys must match the names used in sql.

    • param_types (dict[str -> Union[dict, *[types.Type](spanner_v1/types.md#google.cloud.spanner_v1.types.Type)]*]) – (Optional) maps explicit types for one or more param values; required if parameters are passed.

    • partition_size_bytes (int) – (Optional) desired size for each partition generated. The service uses this as a hint, the actual partition size may differ.

    • max_partitions (int) – (Optional) desired maximum number of partitions generated. The service uses this as a hint, the actual number of partitions may differ.

    • retry (Retry) – (Optional) The retry settings for this request.

    • timeout (float) – (Optional) The timeout for this request.

  • Return type

    iterable of bytes

  • Returns

    a sequence of partition tokens

  • Raises

    ValueError – for single-use snapshots, or if a transaction ID is already associated with the snapshot.

partition_read(table, columns, keyset, index='', partition_size_bytes=None, max_partitions=None, *, retry=<_MethodDefault._DEFAULT_VALUE:

Perform a PartitionRead API request for rows in a table.

  • Parameters

    • table (str) – name of the table from which to fetch data

    • columns (list of str) – names of columns to be retrieved

    • keyset (KeySet) – keys / ranges identifying rows to be retrieved

    • index (str) – (Optional) name of index to use, rather than the table’s primary key

    • partition_size_bytes (int) – (Optional) desired size for each partition generated. The service uses this as a hint, the actual partition size may differ.

    • max_partitions (int) – (Optional) desired maximum number of partitions generated. The service uses this as a hint, the actual number of partitions may differ.

    • retry (Retry) – (Optional) The retry settings for this request.

    • timeout (float) – (Optional) The timeout for this request.

  • Return type

    iterable of bytes

  • Returns

    a sequence of partition tokens

  • Raises

    ValueError – for single-use snapshots, or if a transaction ID is already associated with the snapshot.

read(table, columns, keyset, index='', limit=0, partition=None, request_options=None, *, retry=<_MethodDefault._DEFAULT_VALUE:

Perform a StreamingRead API request for rows in a table.

  • Parameters

    • table (str) – name of the table from which to fetch data

    • columns (list of str) – names of columns to be retrieved

    • keyset (KeySet) – keys / ranges identifying rows to be retrieved

    • index (str) – (Optional) name of index to use, rather than the table’s primary key

    • limit (int) – (Optional) maximum number of rows to return. Incompatible with partition.

    • partition (bytes) – (Optional) one of the partition tokens returned from partition_read(). Incompatible with limit.

    • request_options (google.cloud.spanner_v1.types.RequestOptions) – (Optional) Common options for this request. If a dict is provided, it must be of the same form as the protobuf message RequestOptions. Please note, the transactionTag setting will be ignored for snapshot as it’s not supported for read-only transactions.

    • retry (Retry) – (Optional) The retry settings for this request.

    • timeout (float) – (Optional) The timeout for this request.

  • Return type

    StreamedResultSet

  • Returns

    a result set instance which can be used to consume rows.

  • Raises

    ValueError – for reuse of single-use snapshots, or if a transaction ID is already pending for multiple-use snapshots.