Merge pull request #994 from bigchaindb/feat/927/implement-mongodb-changefeed

[WIP] Implement mongodb changefeed

bigchaindb/backend/mongodb/__init__.py

@@ -16,7 +16,7 @@ generic backend interfaces to the implementations in this module.
 """
 
 # Register the single dispatched modules on import.
-from bigchaindb.backend.mongodb import schema, query  # noqa no changefeed for now
+from bigchaindb.backend.mongodb import schema, query, changefeed  # noqa
 
 # MongoDBConnection should always be accessed via
 # ``bigchaindb.backend.connect()``.

bigchaindb/backend/mongodb/changefeed.py

@@ -0,0 +1,94 @@
+import logging
+import time
+
+import pymongo
+from pymongo.errors import ConnectionFailure, OperationFailure
+
+from bigchaindb import backend
+from bigchaindb.backend.changefeed import ChangeFeed
+from bigchaindb.backend.utils import module_dispatch_registrar
+from bigchaindb.backend.mongodb.connection import MongoDBConnection
+
+
+logger = logging.getLogger(__name__)
+register_changefeed = module_dispatch_registrar(backend.changefeed)
+
+
+class MongoDBChangeFeed(ChangeFeed):
+    """This class implements a MongoDB changefeed.
+
+    We emulate the behaviour of the RethinkDB changefeed by using a tailable
+    cursor that listens for events on the oplog.
+    """
+
+    def run_forever(self):
+        for element in self.prefeed:
+            self.outqueue.put(element)
+
+        while True:
+            try:
+                self.run_changefeed()
+                break
+            except (ConnectionFailure, OperationFailure) as exc:
+                logger.exception(exc)
+                time.sleep(1)
+
+    def run_changefeed(self):
+        dbname = self.connection.dbname
+        table = self.table
+        namespace = '{}.{}'.format(dbname, table)
+        # last timestamp in the oplog. We only care for operations happening
+        # in the future.
+        last_ts = self.connection.conn.local.oplog.rs.find()\
+                      .sort('$natural', pymongo.DESCENDING).limit(1)\
+                      .next()['ts']
+        # tailable cursor. A tailable cursor will remain open even after the
+        # last result was returned. ``TAILABLE_AWAIT`` will block for some
+        # timeout after the last result was returned. If no result is received
+        # in the meantime it will raise a StopIteration excetiption.
+        cursor = self.connection.conn.local.oplog.rs.find(
+            {'ns': namespace, 'ts': {'$gt': last_ts}},
+            cursor_type=pymongo.CursorType.TAILABLE_AWAIT
+        )
+
+        while cursor.alive:
+            try:
+                record = cursor.next()
+            except StopIteration:
+                continue
+
+            is_insert = record['op'] == 'i'
+            is_delete = record['op'] == 'd'
+            is_update = record['op'] == 'u'
+
+            # mongodb documents uses the `_id` for the primary key.
+            # We are not using this field at this point and we need to
+            # remove it to prevent problems with schema validation.
+            # See https://github.com/bigchaindb/bigchaindb/issues/992
+            if is_insert and (self.operation & ChangeFeed.INSERT):
+                record['o'].pop('_id', None)
+                doc = record['o']
+            elif is_delete and (self.operation & ChangeFeed.DELETE):
+                # on delete it only returns the id of the document
+                doc = record['o']
+            elif is_update and (self.operation & ChangeFeed.UPDATE):
+                # the oplog entry for updates only returns the update
+                # operations to apply to the document and not the
+                # document itself. So here we first read the document
+                # and then return it.
+                doc = self.connection.conn[dbname][table]\
+                        .find_one(record['o2'], projection={'_id': False})
+            self.outqueue.put(doc)
+
+
+@register_changefeed(MongoDBConnection)
+def get_changefeed(connection, table, operation, *, prefeed=None):
+    """Return a MongoDB changefeed.
+
+    Returns:
+        An instance of
+        :class:`~bigchaindb.backend.mongodb.MongoDBChangeFeed`.
+    """
+
+    return MongoDBChangeFeed(table, operation, prefeed=prefeed,
+                             connection=connection)

bigchaindb/backend/mongodb/query.py

@@ -20,10 +20,12 @@ def write_transaction(conn, signed_transaction):
 
 @register_query(MongoDBConnection)
 def update_transaction(conn, transaction_id, doc):
+    # with mongodb we need to add update operators to the doc
+    doc = {'$set': doc}
     return conn.db['backlog']\
-            .find_one_and_update({'id': transaction_id},
-                                 doc,
-                                 return_document=ReturnDocument.AFTER)
+               .find_one_and_update({'id': transaction_id},
+                                    doc,
+                                    return_document=ReturnDocument.AFTER)
 
 
 @register_query(MongoDBConnection)
@@ -38,10 +40,20 @@ def get_stale_transactions(conn, reassign_delay):
 
 
 @register_query(MongoDBConnection)
-def get_transaction_from_block(conn, block_id, tx_id):
-    # this is definitely wrong, but it's something like this
-    return conn.db['bigchain'].find_one({'id': block_id,
-                                         'block.transactions.id': tx_id})
+def get_transaction_from_block(conn, transaction_id, block_id):
+    return conn.db['bigchain'].aggregate([
+        {'$match': {'id': block_id}},
+        {'$project': {
+            'block.transactions': {
+                '$filter': {
+                    'input': '$block.transactions',
+                    'as': 'transaction',
+                    'cond': {
+                        '$eq': ['$$transaction.id', transaction_id]
+                    }
+                }
+            }
+        }}]).next()['block']['transactions'][0]
 
 
 @register_query(MongoDBConnection)
@@ -90,14 +102,16 @@ def get_owned_ids(conn, owner):
 @register_query(MongoDBConnection)
 def get_votes_by_block_id(conn, block_id):
     return conn.db['votes']\
-            .find({'vote.voting_for_block': block_id})
+            .find({'vote.voting_for_block': block_id},
+                  projection={'_id': False})
 
 
 @register_query(MongoDBConnection)
 def get_votes_by_block_id_and_voter(conn, block_id, node_pubkey):
     return conn.db['votes']\
             .find({'vote.voting_for_block': block_id,
-                   'node_pubkey': node_pubkey})
+                   'node_pubkey': node_pubkey},
+                  projection={'_id': False})
 
 
 @register_query(MongoDBConnection)
@@ -133,8 +147,9 @@ def write_vote(conn, vote):
 
 @register_query(MongoDBConnection)
 def get_genesis_block(conn):
-    return conn.db['bigchain'].find_one({'block.transactions.0.operation' ==
-                                         'GENESIS'})
+    return conn.db['bigchain'].find_one({
+        'block.transactions.0.operation': 'GENESIS'
+    })
 
 
 @register_query(MongoDBConnection)
@@ -142,7 +157,10 @@ def get_last_voted_block(conn, node_pubkey):
     last_voted = conn.db['votes']\
                   .find({'node_pubkey': node_pubkey},
                         sort=[('vote.timestamp', -1)])
-    if not last_voted:
+
+    # pymongo seems to return a cursor even if there are no results
+    # so we actually need to check the count
+    if last_voted.count() == 0:
         return get_genesis_block(conn)
 
     mapping = {v['vote']['previous_block']: v['vote']['voting_for_block']

bigchaindb/backend/mongodb/schema.py

@@ -61,13 +61,12 @@ def create_bigchain_secondary_index(conn, dbname):
 
     # to query the bigchain for a transaction id, this field is unique
     conn.conn[dbname]['bigchain'].create_index('block.transactions.id',
-                                               name='transaction_id',
-                                               unique=True)
+                                               name='transaction_id')
 
     # secondary index for asset uuid, this field is unique
     conn.conn[dbname]['bigchain']\
         .create_index('block.transactions.transaction.asset.id',
-                      name='asset_id', unique=True)
+                      name='asset_id')
 
 
 def create_backlog_secondary_index(conn, dbname):

bigchaindb/pipelines/stale.py

@@ -48,6 +48,8 @@ class StaleTransactionMonitor:
         Returns:
             transaction
         """
+        # NOTE: Maybe this is to verbose?
+        logger.info('Reassigning transaction with id %s', tx['id'])
         self.bigchain.reassign_transaction(tx)
         return tx
 

bigchaindb/pipelines/vote.py

@@ -5,10 +5,10 @@ of actions to do on transactions is specified in the ``create_pipeline``
 function.
 """
 
+import logging
 from collections import Counter
 
 from multipipes import Pipeline, Node
-from bigchaindb.common import exceptions
 
 import bigchaindb
 from bigchaindb import Bigchain
@@ -16,6 +16,10 @@ from bigchaindb import backend
 from bigchaindb.backend.changefeed import ChangeFeed
 from bigchaindb.consensus import BaseConsensusRules
 from bigchaindb.models import Transaction, Block
+from bigchaindb.common import exceptions
+
+
+logger = logging.getLogger(__name__)
 
 
 class Vote:
@@ -132,7 +136,9 @@ class Vote:
         Args:
             vote: the vote to write.
         """
-
+        validity = 'valid' if vote['vote']['is_block_valid'] else 'invalid'
+        logger.info("Voting '%s' for block %s", validity,
+                    vote['vote']['voting_for_block'])
         self.bigchain.write_vote(vote)
         return vote
 

tests/db/test_bigchain_api.py

@@ -153,14 +153,14 @@ class TestBigchainApi(object):
     def test_get_transaction_in_invalid_and_valid_block(self, monkeypatch, b):
         from bigchaindb.models import Transaction
 
-        monkeypatch.setattr('time.time', lambda: 1)
+        monkeypatch.setattr('time.time', lambda: 1000000000)
         tx1 = Transaction.create([b.me], [([b.me], 1)],
                                  metadata={'msg': random.random()})
         tx1 = tx1.sign([b.me_private])
         block1 = b.create_block([tx1])
         b.write_block(block1)
 
-        monkeypatch.setattr('time.time', lambda: 2222222222)
+        monkeypatch.setattr('time.time', lambda: 2000000000)
         tx2 = Transaction.create([b.me], [([b.me], 1)],
                                  metadata={'msg': random.random()})
         tx2 = tx2.sign([b.me_private])