diff options
Diffstat (limited to 'synapse/storage/util/sequence.py')
| -rw-r--r-- | synapse/storage/util/sequence.py | 90 |
1 files changed, 88 insertions, 2 deletions
diff --git a/synapse/storage/util/sequence.py b/synapse/storage/util/sequence.py index ffc1894748..2dd95e2709 100644 --- a/synapse/storage/util/sequence.py +++ b/synapse/storage/util/sequence.py @@ -13,11 +13,34 @@ # See the License for the specific language governing permissions and # limitations under the License. import abc +import logging import threading from typing import Callable, List, Optional -from synapse.storage.engines import BaseDatabaseEngine, PostgresEngine -from synapse.storage.types import Cursor +from synapse.storage.engines import ( + BaseDatabaseEngine, + IncorrectDatabaseSetup, + PostgresEngine, +) +from synapse.storage.types import Connection, Cursor + +logger = logging.getLogger(__name__) + + +_INCONSISTENT_SEQUENCE_ERROR = """ +Postgres sequence '%(seq)s' is inconsistent with associated +table '%(table)s'. This can happen if Synapse has been downgraded and +then upgraded again, or due to a bad migration. + +To fix this error, shut down Synapse (including any and all workers) +and run the following SQL: + + SELECT setval('%(seq)s', ( + %(max_id_sql)s + )); + +See docs/postgres.md for more information. +""" class SequenceGenerator(metaclass=abc.ABCMeta): @@ -28,6 +51,19 @@ class SequenceGenerator(metaclass=abc.ABCMeta): """Gets the next ID in the sequence""" ... + @abc.abstractmethod + def check_consistency( + self, db_conn: Connection, table: str, id_column: str, positive: bool = True + ): + """Should be called during start up to test that the current value of + the sequence is greater than or equal to the maximum ID in the table. + + This is to handle various cases where the sequence value can get out + of sync with the table, e.g. if Synapse gets rolled back to a previous + version and the rolled forwards again. + """ + ... + class PostgresSequenceGenerator(SequenceGenerator): """An implementation of SequenceGenerator which uses a postgres sequence""" @@ -45,6 +81,50 @@ class PostgresSequenceGenerator(SequenceGenerator): ) return [i for (i,) in txn] + def check_consistency( + self, db_conn: Connection, table: str, id_column: str, positive: bool = True + ): + txn = db_conn.cursor() + + # First we get the current max ID from the table. + table_sql = "SELECT GREATEST(%(agg)s(%(id)s), 0) FROM %(table)s" % { + "id": id_column, + "table": table, + "agg": "MAX" if positive else "-MIN", + } + + txn.execute(table_sql) + row = txn.fetchone() + if not row: + # Table is empty, so nothing to do. + txn.close() + return + + # Now we fetch the current value from the sequence and compare with the + # above. + max_stream_id = row[0] + txn.execute( + "SELECT last_value, is_called FROM %(seq)s" % {"seq": self._sequence_name} + ) + last_value, is_called = txn.fetchone() + txn.close() + + # If `is_called` is False then `last_value` is actually the value that + # will be generated next, so we decrement to get the true "last value". + if not is_called: + last_value -= 1 + + if max_stream_id > last_value: + logger.warning( + "Postgres sequence %s is behind table %s: %d < %d", + last_value, + max_stream_id, + ) + raise IncorrectDatabaseSetup( + _INCONSISTENT_SEQUENCE_ERROR + % {"seq": self._sequence_name, "table": table, "max_id_sql": table_sql} + ) + GetFirstCallbackType = Callable[[Cursor], int] @@ -81,6 +161,12 @@ class LocalSequenceGenerator(SequenceGenerator): self._current_max_id += 1 return self._current_max_id + def check_consistency( + self, db_conn: Connection, table: str, id_column: str, positive: bool = True + ): + # There is nothing to do for in memory sequences + pass + def build_sequence_generator( database_engine: BaseDatabaseEngine, |