8d544d643d
This patch forces MessageController.claimed to always query the primary in order to resolve a race condition in ClaimController.create. The latter method tags a batch of messages with a claim ID, then immediately calles claimed() to get a list of messages that were actually updated. MessageController.claimed is also used by ClaimController.update, so that request will no longer read from secondaries either. This shouldn't put much more load on the primary, and may even be desired behavior in the case that a client creates a claim and immediately attempts to update it, in which case they could get a "not found" if the new claim hasn't propagated yet to the secondary being queried. Change-Id: I8b5cfee1cc6f185ebf53e98fad95a5fc30e021da Partial-Bug: #1218990
233 lines
7.8 KiB
Python
233 lines
7.8 KiB
Python
# Copyright (c) 2013 Red Hat, Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
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# implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Implements the MongoDB storage controller for claims.
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Field Mappings:
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In order to reduce the disk / memory space used,
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field names will be, most of the time, the first
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letter of their long name.
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"""
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import datetime
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from bson import objectid
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import marconi.openstack.common.log as logging
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from marconi.openstack.common import timeutils
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from marconi import storage
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from marconi.storage import exceptions
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from marconi.storage.mongodb import utils
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LOG = logging.getLogger(__name__)
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class ClaimController(storage.ClaimBase):
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"""Implements claim resource operations using MongoDB.
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No dedicated collection is being used
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for claims.
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Claims are created in the messages
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collection and live within messages, that is,
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in the c field.
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This implementation certainly uses more space
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on disk but reduces the number of queries to
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be executed and the time needed to retrieve
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claims and claimed messages.
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As for the memory usage, this implementation
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requires less memory since a single index is
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required. The index is a compound index between
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the claim id and it's expiration timestamp.
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"""
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@utils.raises_conn_error
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def get(self, queue, claim_id, project=None):
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msg_ctrl = self.driver.message_controller
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# Base query, always check expire time
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now = timeutils.utcnow()
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cid = utils.to_oid(claim_id)
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if cid is None:
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raise exceptions.ClaimDoesNotExist(queue, project, claim_id)
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def messages(msg_iter):
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msg = next(msg_iter)
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yield msg.pop('claim')
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yield msg
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# Smoke it!
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for msg in msg_iter:
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del msg['claim']
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yield msg
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try:
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# Lets get claim's data
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# from the first message
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# in the iterator
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msgs = messages(msg_ctrl.claimed(queue, cid, now,
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project=project))
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claim = next(msgs)
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update_time = claim['e'] - datetime.timedelta(seconds=claim['t'])
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age = timeutils.delta_seconds(update_time, now)
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claim = {
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'age': int(age),
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'ttl': claim.pop('t'),
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'id': str(claim['id']),
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}
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except StopIteration:
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raise exceptions.ClaimDoesNotExist(cid, queue, project)
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return (claim, msgs)
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@utils.raises_conn_error
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def create(self, queue, metadata, project=None, limit=10):
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"""Creates a claim.
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This implementation was done in a best-effort fashion.
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In order to create a claim we need to get a list
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of messages that can be claimed. Once we have that
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list we execute a query filtering by the ids returned
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by the previous query.
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Since there's a lot of space for race conditions here,
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we'll check if the number of updated records is equal to
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the max number of messages to claim. If the number of updated
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messages is lower than limit we'll try to claim the remaining
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number of messages.
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This 2 queries are required because there's no way, as for the
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time being, to execute an update on a limited number of records.
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"""
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msg_ctrl = self.driver.message_controller
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ttl = metadata['ttl']
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grace = metadata['grace']
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oid = objectid.ObjectId()
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now = timeutils.utcnow()
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ttl_delta = datetime.timedelta(seconds=ttl)
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claim_expires = now + ttl_delta
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grace_delta = datetime.timedelta(seconds=grace)
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message_expires = claim_expires + grace_delta
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message_ttl = ttl + grace
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meta = {
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'id': oid,
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't': ttl,
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'e': claim_expires,
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}
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# Get a list of active, not claimed nor expired
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# messages that could be claimed.
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msgs = msg_ctrl.active(queue, fields={'_id': 1}, project=project)
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msgs = msgs.limit(limit)
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messages = iter([])
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ids = [msg['_id'] for msg in msgs]
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if len(ids) == 0:
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return (None, messages)
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now = timeutils.utcnow()
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# Set claim field for messages in ids
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updated = msg_ctrl._col.update({'_id': {'$in': ids},
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'$or': [
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{'c.id': None},
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{
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'c.id': {'$ne': None},
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'c.e': {'$lte': now}
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}
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]},
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{'$set': {'c': meta}}, upsert=False,
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multi=True)['n']
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# NOTE(flaper87): Dirty hack!
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# This sets the expiration time to
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# `expires` on messages that would
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# expire before claim.
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new_values = {'e': message_expires, 't': message_ttl}
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msg_ctrl._col.update({'q': queue,
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'p': project,
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'e': {'$lt': message_expires},
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'c.id': oid},
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{'$set': new_values},
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upsert=False, multi=True)
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if updated != 0:
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# NOTE(kgriffs): This extra step is necessary because
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# in between having gotten a list of active messages
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# and updating them, some of them may have been
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# claimed by a parallel request. Therefore, we need
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# to find out which messages were actually tagged
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# with the claim ID successfully.
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claim, messages = self.get(queue, oid, project=project)
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return (str(oid), messages)
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@utils.raises_conn_error
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def update(self, queue, claim_id, metadata, project=None):
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cid = utils.to_oid(claim_id)
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if cid is None:
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raise exceptions.ClaimDoesNotExist(claim_id, queue, project)
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now = timeutils.utcnow()
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ttl = int(metadata.get('ttl', 60))
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ttl_delta = datetime.timedelta(seconds=ttl)
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expires = now + ttl_delta
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msg_ctrl = self.driver.message_controller
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claimed = msg_ctrl.claimed(queue, cid, expires=now,
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limit=1, project=project)
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try:
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next(claimed)
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except StopIteration:
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raise exceptions.ClaimDoesNotExist(claim_id, queue, project)
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meta = {
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'id': cid,
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't': ttl,
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'e': expires,
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}
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msg_ctrl._col.update({'q': queue, 'p': project, 'c.id': cid},
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{'$set': {'c': meta}},
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upsert=False, multi=True)
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# NOTE(flaper87): Dirty hack!
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# This sets the expiration time to
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# `expires` on messages that would
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# expire before claim.
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msg_ctrl._col.update({'q': queue,
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'p': project,
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'e': {'$lt': expires},
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'c.id': cid},
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{'$set': {'e': expires, 't': ttl}},
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upsert=False, multi=True)
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@utils.raises_conn_error
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def delete(self, queue, claim_id, project=None):
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msg_ctrl = self.driver.message_controller
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msg_ctrl.unclaim(queue, claim_id, project=project)
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