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async_transaction.py
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async_transaction.py
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# Copyright 2020 Google LLC All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Helpers for applying Google Cloud Firestore changes in a transaction."""
import asyncio
import random
from google.cloud.firestore_v1.base_transaction import (
_BaseTransactional,
BaseTransaction,
MAX_ATTEMPTS,
_CANT_BEGIN,
_CANT_ROLLBACK,
_CANT_COMMIT,
_WRITE_READ_ONLY,
_INITIAL_SLEEP,
_MAX_SLEEP,
_MULTIPLIER,
_EXCEED_ATTEMPTS_TEMPLATE,
)
from google.api_core import exceptions
from google.cloud.firestore_v1 import async_batch
from google.cloud.firestore_v1.async_document import AsyncDocumentReference
from google.cloud.firestore_v1.async_query import AsyncQuery
class AsyncTransaction(async_batch.AsyncWriteBatch, BaseTransaction):
"""Accumulate read-and-write operations to be sent in a transaction.
Args:
client (:class:`~google.cloud.firestore_v1.client.Client`):
The client that created this transaction.
max_attempts (Optional[int]): The maximum number of attempts for
the transaction (i.e. allowing retries). Defaults to
:attr:`~google.cloud.firestore_v1.transaction.MAX_ATTEMPTS`.
read_only (Optional[bool]): Flag indicating if the transaction
should be read-only or should allow writes. Defaults to
:data:`False`.
"""
def __init__(self, client, max_attempts=MAX_ATTEMPTS, read_only=False):
super(AsyncTransaction, self).__init__(client)
BaseTransaction.__init__(self, max_attempts, read_only)
def _add_write_pbs(self, write_pbs):
"""Add `Write`` protobufs to this transaction.
Args:
write_pbs (List[google.cloud.proto.firestore.v1.\
write.Write]): A list of write protobufs to be added.
Raises:
ValueError: If this transaction is read-only.
"""
if self._read_only:
raise ValueError(_WRITE_READ_ONLY)
super(AsyncTransaction, self)._add_write_pbs(write_pbs)
async def _begin(self, retry_id=None):
"""Begin the transaction.
Args:
retry_id (Optional[bytes]): Transaction ID of a transaction to be
retried.
Raises:
ValueError: If the current transaction has already begun.
"""
if self.in_progress:
msg = _CANT_BEGIN.format(self._id)
raise ValueError(msg)
transaction_response = await self._client._firestore_api.begin_transaction(
request={
"database": self._client._database_string,
"options": self._options_protobuf(retry_id),
},
metadata=self._client._rpc_metadata,
)
self._id = transaction_response.transaction
async def _rollback(self):
"""Roll back the transaction.
Raises:
ValueError: If no transaction is in progress.
"""
if not self.in_progress:
raise ValueError(_CANT_ROLLBACK)
try:
# NOTE: The response is just ``google.protobuf.Empty``.
await self._client._firestore_api.rollback(
request={
"database": self._client._database_string,
"transaction": self._id,
},
metadata=self._client._rpc_metadata,
)
finally:
self._clean_up()
async def _commit(self):
"""Transactionally commit the changes accumulated.
Returns:
List[:class:`google.cloud.proto.firestore.v1.write.WriteResult`, ...]:
The write results corresponding to the changes committed, returned
in the same order as the changes were applied to this transaction.
A write result contains an ``update_time`` field.
Raises:
ValueError: If no transaction is in progress.
"""
if not self.in_progress:
raise ValueError(_CANT_COMMIT)
commit_response = await _commit_with_retry(
self._client, self._write_pbs, self._id
)
self._clean_up()
return list(commit_response.write_results)
async def get_all(self, references):
"""Retrieves multiple documents from Firestore.
Args:
references (List[.AsyncDocumentReference, ...]): Iterable of document
references to be retrieved.
Yields:
.DocumentSnapshot: The next document snapshot that fulfills the
query, or :data:`None` if the document does not exist.
"""
return await self._client.get_all(references, transaction=self)
async def get(self, ref_or_query):
"""
Retrieve a document or a query result from the database.
Args:
ref_or_query The document references or query object to return.
Yields:
.DocumentSnapshot: The next document snapshot that fulfills the
query, or :data:`None` if the document does not exist.
"""
if isinstance(ref_or_query, AsyncDocumentReference):
return await self._client.get_all([ref_or_query], transaction=self)
elif isinstance(ref_or_query, AsyncQuery):
return await ref_or_query.stream(transaction=self)
else:
raise ValueError(
'Value for argument "ref_or_query" must be a AsyncDocumentReference or a AsyncQuery.'
)
class _AsyncTransactional(_BaseTransactional):
"""Provide a callable object to use as a transactional decorater.
This is surfaced via
:func:`~google.cloud.firestore_v1.async_transaction.transactional`.
Args:
to_wrap (Callable[[:class:`~google.cloud.firestore_v1.async_transaction.AsyncTransaction`, ...], Any]):
A callable that should be run (and retried) in a transaction.
"""
def __init__(self, to_wrap):
super(_AsyncTransactional, self).__init__(to_wrap)
async def _pre_commit(self, transaction, *args, **kwargs):
"""Begin transaction and call the wrapped callable.
If the callable raises an exception, the transaction will be rolled
back. If not, the transaction will be "ready" for ``Commit`` (i.e.
it will have staged writes).
Args:
transaction
(:class:`~google.cloud.firestore_v1.async_transaction.AsyncTransaction`):
A transaction to execute the callable within.
args (Tuple[Any, ...]): The extra positional arguments to pass
along to the wrapped callable.
kwargs (Dict[str, Any]): The extra keyword arguments to pass
along to the wrapped callable.
Returns:
Any: result of the wrapped callable.
Raises:
Exception: Any failure caused by ``to_wrap``.
"""
# Force the ``transaction`` to be not "in progress".
transaction._clean_up()
await transaction._begin(retry_id=self.retry_id)
# Update the stored transaction IDs.
self.current_id = transaction._id
if self.retry_id is None:
self.retry_id = self.current_id
try:
return self.to_wrap(transaction, *args, **kwargs)
except: # noqa
# NOTE: If ``rollback`` fails this will lose the information
# from the original failure.
await transaction._rollback()
raise
async def _maybe_commit(self, transaction):
"""Try to commit the transaction.
If the transaction is read-write and the ``Commit`` fails with the
``ABORTED`` status code, it will be retried. Any other failure will
not be caught.
Args:
transaction
(:class:`~google.cloud.firestore_v1.transaction.Transaction`):
The transaction to be ``Commit``-ed.
Returns:
bool: Indicating if the commit succeeded.
"""
try:
await transaction._commit()
return True
except exceptions.GoogleAPICallError as exc:
if transaction._read_only:
raise
if isinstance(exc, exceptions.Aborted):
# If a read-write transaction returns ABORTED, retry.
return False
else:
raise
async def __call__(self, transaction, *args, **kwargs):
"""Execute the wrapped callable within a transaction.
Args:
transaction
(:class:`~google.cloud.firestore_v1.transaction.Transaction`):
A transaction to execute the callable within.
args (Tuple[Any, ...]): The extra positional arguments to pass
along to the wrapped callable.
kwargs (Dict[str, Any]): The extra keyword arguments to pass
along to the wrapped callable.
Returns:
Any: The result of the wrapped callable.
Raises:
ValueError: If the transaction does not succeed in
``max_attempts``.
"""
self._reset()
for attempt in range(transaction._max_attempts):
result = await self._pre_commit(transaction, *args, **kwargs)
succeeded = await self._maybe_commit(transaction)
if succeeded:
return result
# Subsequent requests will use the failed transaction ID as part of
# the ``BeginTransactionRequest`` when restarting this transaction
# (via ``options.retry_transaction``). This preserves the "spot in
# line" of the transaction, so exponential backoff is not required
# in this case.
await transaction._rollback()
msg = _EXCEED_ATTEMPTS_TEMPLATE.format(transaction._max_attempts)
raise ValueError(msg)
def async_transactional(to_wrap):
"""Decorate a callable so that it runs in a transaction.
Args:
to_wrap
(Callable[[:class:`~google.cloud.firestore_v1.transaction.Transaction`, ...], Any]):
A callable that should be run (and retried) in a transaction.
Returns:
Callable[[:class:`~google.cloud.firestore_v1.transaction.Transaction`, ...], Any]:
the wrapped callable.
"""
return _AsyncTransactional(to_wrap)
async def _commit_with_retry(client, write_pbs, transaction_id):
"""Call ``Commit`` on the GAPIC client with retry / sleep.
Retries the ``Commit`` RPC on Unavailable. Usually this RPC-level
retry is handled by the underlying GAPICd client, but in this case it
doesn't because ``Commit`` is not always idempotent. But here we know it
is "idempotent"-like because it has a transaction ID. We also need to do
our own retry to special-case the ``INVALID_ARGUMENT`` error.
Args:
client (:class:`~google.cloud.firestore_v1.client.Client`):
A client with GAPIC client and configuration details.
write_pbs (List[:class:`google.cloud.proto.firestore.v1.write.Write`, ...]):
A ``Write`` protobuf instance to be committed.
transaction_id (bytes):
ID of an existing transaction that this commit will run in.
Returns:
:class:`google.cloud.firestore_v1.types.CommitResponse`:
The protobuf response from ``Commit``.
Raises:
~google.api_core.exceptions.GoogleAPICallError: If a non-retryable
exception is encountered.
"""
current_sleep = _INITIAL_SLEEP
while True:
try:
return await client._firestore_api.commit(
request={
"database": client._database_string,
"writes": write_pbs,
"transaction": transaction_id,
},
metadata=client._rpc_metadata,
)
except exceptions.ServiceUnavailable:
# Retry
pass
current_sleep = await _sleep(current_sleep)
async def _sleep(current_sleep, max_sleep=_MAX_SLEEP, multiplier=_MULTIPLIER):
"""Sleep and produce a new sleep time.
.. _Exponential Backoff And Jitter: https://www.awsarchitectureblog.com/\
2015/03/backoff.html
Select a duration between zero and ``current_sleep``. It might seem
counterintuitive to have so much jitter, but
`Exponential Backoff And Jitter`_ argues that "full jitter" is
the best strategy.
Args:
current_sleep (float): The current "max" for sleep interval.
max_sleep (Optional[float]): Eventual "max" sleep time
multiplier (Optional[float]): Multiplier for exponential backoff.
Returns:
float: Newly doubled ``current_sleep`` or ``max_sleep`` (whichever
is smaller)
"""
actual_sleep = random.uniform(0.0, current_sleep)
await asyncio.sleep(actual_sleep)
return min(multiplier * current_sleep, max_sleep)