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Diffstat (limited to 'synapse/storage/stream.py')
| -rw-r--r-- | synapse/storage/stream.py | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/synapse/storage/stream.py b/synapse/storage/stream.py index 87fc978813..18c1002e2c 100644 --- a/synapse/storage/stream.py +++ b/synapse/storage/stream.py @@ -13,6 +13,26 @@ # See the License for the specific language governing permissions and # limitations under the License. +""" This module is responsible for getting events from the DB for pagination +and event streaming. + +The order it returns events in depend on whether we are streaming forwards or +are paginating backwards. We do this because we want to handle out of order +messages nicely, while still returning them in the correct order when we +paginate bacwards. + +This is implemented by keeping two ordering columns: stream_ordering and +topological_ordering. Stream ordering is basically insertion/received order +(except for events from backfill requests). The topolgical_ordering is a +weak ordering of events based on the pdu graph. + +This means that we have to have two different types of tokens, depending on +what sort order was used: + - stream tokens are of the form: "s%d", which maps directly to the column + - topological tokems: "t%d-%d", where the integers map to the topological + and stream ordering columns respectively. +""" + from twisted.internet import defer from ._base import SQLBaseStore |