Class BatchSnapshot (3.50.1)

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BatchSnapshot(
    database,
    read_timestamp=None,
    exact_staleness=None,
    session_id=None,
    transaction_id=None,
)

Wrapper for generating and processing read / query batches.

Parameters
Name	Description
database	Database database to use
read_timestamp	datetime.datetime Execute all reads at the given timestamp.
exact_staleness	datetime.timedelta Execute all reads at a timestamp that is exact_staleness old.

Methods

close

close()

Clean up underlying session.

Note: If the transaction has been shared across multiple machines, calling this on any machine would invalidate the transaction everywhere. Ideally this would be called when data has been read from all the partitions.

execute_sql

execute_sql(*args, **kw)

Convenience method: perform query operation via snapshot.

See execute_sql.

from_dict

from_dict(database, mapping)

Reconstruct an instance from a mapping.

Parameters
Name	Description
database	Database database to use
mapping	mapping serialized state of the instance

generate_query_batches

generate_query_batches(
    sql,
    params=None,
    param_types=None,
    partition_size_bytes=None,
    max_partitions=None,
    query_options=None,
    data_boost_enabled=False,
    directed_read_options=None,
    *,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE
)

Start a partitioned query operation.

Uses the PartitionQuery API request to start a partitioned query operation. Returns a list of batch information needed to perform the actual queries.

Parameters
Name	Description
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]] (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.
query_options	QueryOptions or dict (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
directed_read_options	DirectedReadOptions or dict (Optional) Request level option used to set the directed_read_options for ExecuteSqlRequests that indicates which replicas or regions should be used for non-transactional queries.
retry	google.api_core.retry.Retry (Optional) The retry settings for this request.
timeout	float (Optional) The timeout for this request.

Returns
Type	Description
iterable of dict	mappings of information used perform actual partitioned reads via process_read_batch.

generate_read_batches

generate_read_batches(
    table,
    columns,
    keyset,
    index="",
    partition_size_bytes=None,
    max_partitions=None,
    data_boost_enabled=False,
    directed_read_options=None,
    *,
    retry=_MethodDefault._DEFAULT_VALUE,
    timeout=_MethodDefault._DEFAULT_VALUE
)

Start a partitioned batch read operation.

Uses the PartitionRead API request to initiate the partitioned read. Returns a list of batch information needed to perform the actual reads.

Parameters
Name	Description
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.
directed_read_options	DirectedReadOptions or dict (Optional) Request level option used to set the directed_read_options for ReadRequests that indicates which replicas or regions should be used for non-transactional reads.
retry	google.api_core.retry.Retry (Optional) The retry settings for this request.
timeout	float (Optional) The timeout for this request.

Returns
Type	Description
iterable of dict	mappings of information used perform actual partitioned reads via process_read_batch.

process

process(batch)

Process a single, partitioned query or read.

Parameter
Name	Description
batch	mapping one of the mappings returned from an earlier call to generate_query_batches.

Exceptions
Type	Description
ValueError	if batch does not contain either 'read' or 'query'

Returns
Type	Description
StreamedResultSet	a result set instance which can be used to consume rows.

process_query_batch

process_query_batch(
    batch, *, retry=_MethodDefault._DEFAULT_VALUE, timeout=_MethodDefault._DEFAULT_VALUE
)

Process a single, partitioned query.

Parameters
Name	Description
batch	mapping one of the mappings returned from an earlier call to generate_query_batches.
retry	google.api_core.retry.Retry (Optional) The retry settings for this request.
timeout	float (Optional) The timeout for this request.

Returns
Type	Description
StreamedResultSet	a result set instance which can be used to consume rows.

process_read_batch

process_read_batch(
    batch, *, retry=_MethodDefault._DEFAULT_VALUE, timeout=_MethodDefault._DEFAULT_VALUE
)

Process a single, partitioned read.

Parameters
Name	Description
batch	mapping one of the mappings returned from an earlier call to generate_read_batches.
retry	google.api_core.retry.Retry (Optional) The retry settings for this request.
timeout	float (Optional) The timeout for this request.

Returns
Type	Description
StreamedResultSet	a result set instance which can be used to consume rows.

read

read(*args, **kw)

Convenience method: perform read operation via snapshot.

See read.

run_partitioned_query

run_partitioned_query(
    sql,
    params=None,
    param_types=None,
    partition_size_bytes=None,
    max_partitions=None,
    query_options=None,
    data_boost_enabled=False,
)

Start a partitioned query operation to get list of partitions and then executes each partition on a separate thread

Parameters
Name	Description
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]] (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.
query_options	QueryOptions or dict (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

Returns
Type	Description
MergedResultSet	a result set instance which can be used to consume rows.

to_dict

to_dict()

Return state as a dictionary.

Result can be used to serialize the instance and reconstitute it later using from_dict.