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Add multi-batch change transaction support for datasync consumers

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Otherwise it was possible for the rattail transaction to fall out of
sync from consumer, if it was committing more often than us.
This commit is contained in:
Lance Edgar 2016-04-21 19:26:28 -05:00
parent d7cb42a98b
commit 295f2d53c4
2 changed files with 31 additions and 10 deletions
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19
rattail/datasync/consumers.py
View file

@ -45,9 +45,26 @@ class DataSyncConsumer(object):
This method is called when the consumer thread is first started.
"""
def begin_transaction(self):
"""
Called just before the consumer is asked to process changes, possibly
via multiple batches.
"""
def process_changes(self, session, changes):
"""
Process (consume) a set of changes.
Process (consume) a batch of changes.
"""
def rollback_transaction(self):
"""
Called when any batch of changes failed to process.
"""
def commit_transaction(self):
"""
Called just after the consumer has successfully finished processing
changes, possibly via multiple batches.
"""

14
rattail/datasync/daemon.py
View file

@ -201,14 +201,15 @@ def consume_changes(profile, consumers):
session = Session()
for consumer in consumers:
changes = session.query(model.DataSyncChange).filter(
model.DataSyncChange.source == profile.key,
model.DataSyncChange.consumer == consumer.key)\
changes = session.query(model.DataSyncChange)\
.filter(model.DataSyncChange.source == profile.key)\
.filter(model.DataSyncChange.consumer == consumer.key)\
.order_by(model.DataSyncChange.obtained)\
.all()
if changes:
log.debug("found {0} changes to process".format(len(changes)))
log.debug("found {} changes to process".format(len(changes)))
consumer.begin_transaction()
# Process (consume) changes in batches, according to timestamp.
batch = []
@ -235,13 +236,16 @@ def consume_changes(profile, consumers):
log.debug("processed {} changes in {} batches{}".format(
changecount, batchcount, " (with errors)" if error else ""))
if error:
consumer.rollback_transaction()
break
else:
consumer.commit_transaction()
if error:
session.rollback()
session.close()
break
else:
session.commit()
session.close()