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.