synapse-product/synapse/storage/background_updates.py

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# Copyright 2014-2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
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import logging
from types import TracebackType
from typing import (
TYPE_CHECKING,
Any,
AsyncContextManager,
Awaitable,
Callable,
Dict,
Iterable,
List,
Optional,
Type,
)
import attr
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.types import Connection, Cursor
from synapse.types import JsonDict
from synapse.util import Clock, json_encoder
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from . import engines
if TYPE_CHECKING:
from synapse.server import HomeServer
from synapse.storage.database import DatabasePool, LoggingTransaction
logger = logging.getLogger(__name__)
ON_UPDATE_CALLBACK = Callable[[str, str, bool], AsyncContextManager[int]]
DEFAULT_BATCH_SIZE_CALLBACK = Callable[[str, str], Awaitable[int]]
MIN_BATCH_SIZE_CALLBACK = Callable[[str, str], Awaitable[int]]
@attr.s(slots=True, frozen=True, auto_attribs=True)
class _BackgroundUpdateHandler:
"""A handler for a given background update.
Attributes:
callback: The function to call to make progress on the background
update.
oneshot: Wether the update is likely to happen all in one go, ignoring
the supplied target duration, e.g. index creation. This is used by
the update controller to help correctly schedule the update.
"""
callback: Callable[[JsonDict, int], Awaitable[int]]
oneshot: bool = False
class _BackgroundUpdateContextManager:
def __init__(
self, sleep: bool, clock: Clock, sleep_duration_ms: int, update_duration: int
):
self._sleep = sleep
self._clock = clock
self._sleep_duration_ms = sleep_duration_ms
self._update_duration_ms = update_duration
async def __aenter__(self) -> int:
if self._sleep:
await self._clock.sleep(self._sleep_duration_ms / 1000)
return self._update_duration_ms
async def __aexit__(
self,
exc_type: Optional[Type[BaseException]],
exc: Optional[BaseException],
tb: Optional[TracebackType],
) -> None:
pass
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class BackgroundUpdatePerformance:
"""Tracks the how long a background update is taking to update its items"""
def __init__(self, name: str):
self.name = name
self.total_item_count = 0
self.total_duration_ms = 0.0
self.avg_item_count = 0.0
self.avg_duration_ms = 0.0
def update(self, item_count: int, duration_ms: float) -> None:
"""Update the stats after doing an update"""
self.total_item_count += item_count
self.total_duration_ms += duration_ms
# Exponential moving averages for the number of items updated and
# the duration.
self.avg_item_count += 0.1 * (item_count - self.avg_item_count)
self.avg_duration_ms += 0.1 * (duration_ms - self.avg_duration_ms)
def average_items_per_ms(self) -> Optional[float]:
"""An estimate of how long it takes to do a single update.
Returns:
A duration in ms as a float
"""
# We want to return None if this is the first background update item
if self.total_item_count == 0:
return None
# Avoid dividing by zero
elif self.avg_duration_ms == 0:
return 0
else:
# Use the exponential moving average so that we can adapt to
# changes in how long the update process takes.
return float(self.avg_item_count) / float(self.avg_duration_ms)
def total_items_per_ms(self) -> Optional[float]:
"""An estimate of how long it takes to do a single update.
Returns:
A duration in ms as a float
"""
if self.total_duration_ms == 0:
return 0
elif self.total_item_count == 0:
return None
else:
return float(self.total_item_count) / float(self.total_duration_ms)
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class BackgroundUpdater:
"""Background updates are updates to the database that run in the
background. Each update processes a batch of data at once. We attempt to
limit the impact of each update by monitoring how long each batch takes to
process and autotuning the batch size.
"""
def __init__(self, hs: "HomeServer", database: "DatabasePool"):
self._clock = hs.get_clock()
self.db_pool = database
self._database_name = database.name()
# if a background update is currently running, its name.
self._current_background_update: Optional[str] = None
self._on_update_callback: Optional[ON_UPDATE_CALLBACK] = None
self._default_batch_size_callback: Optional[DEFAULT_BATCH_SIZE_CALLBACK] = None
self._min_batch_size_callback: Optional[MIN_BATCH_SIZE_CALLBACK] = None
self._background_update_performance: Dict[str, BackgroundUpdatePerformance] = {}
self._background_update_handlers: Dict[str, _BackgroundUpdateHandler] = {}
self._all_done = False
# Whether we're currently running updates
self._running = False
# Whether background updates are enabled. This allows us to
# enable/disable background updates via the admin API.
self.enabled = True
self.minimum_background_batch_size = hs.config.background_updates.min_batch_size
self.default_background_batch_size = (
hs.config.background_updates.default_batch_size
)
self.update_duration_ms = hs.config.background_updates.update_duration_ms
self.sleep_duration_ms = hs.config.background_updates.sleep_duration_ms
self.sleep_enabled = hs.config.background_updates.sleep_enabled
def register_update_controller_callbacks(
self,
on_update: ON_UPDATE_CALLBACK,
default_batch_size: Optional[DEFAULT_BATCH_SIZE_CALLBACK] = None,
min_batch_size: Optional[DEFAULT_BATCH_SIZE_CALLBACK] = None,
) -> None:
"""Register callbacks from a module for each hook."""
if self._on_update_callback is not None:
logger.warning(
"More than one module tried to register callbacks for controlling"
" background updates. Only the callbacks registered by the first module"
" (in order of appearance in Synapse's configuration file) that tried to"
" do so will be called."
)
return
self._on_update_callback = on_update
if default_batch_size is not None:
self._default_batch_size_callback = default_batch_size
if min_batch_size is not None:
self._min_batch_size_callback = min_batch_size
def _get_context_manager_for_update(
self,
sleep: bool,
update_name: str,
database_name: str,
oneshot: bool,
) -> AsyncContextManager[int]:
"""Get a context manager to run a background update with.
If a module has registered a `update_handler` callback, use the context manager
it returns.
Otherwise, returns a context manager that will return a default value, optionally
sleeping if needed.
Args:
sleep: Whether we can sleep between updates.
update_name: The name of the update.
database_name: The name of the database the update is being run on.
oneshot: Whether the update will complete all in one go, e.g. index creation.
In such cases the returned target duration is ignored.
Returns:
The target duration in milliseconds that the background update should run for.
Note: this is a *target*, and an iteration may take substantially longer or
shorter.
"""
if self._on_update_callback is not None:
return self._on_update_callback(update_name, database_name, oneshot)
return _BackgroundUpdateContextManager(
sleep, self._clock, self.sleep_duration_ms, self.update_duration_ms
)
async def _default_batch_size(self, update_name: str, database_name: str) -> int:
"""The batch size to use for the first iteration of a new background
update.
"""
if self._default_batch_size_callback is not None:
return await self._default_batch_size_callback(update_name, database_name)
return self.default_background_batch_size
async def _min_batch_size(self, update_name: str, database_name: str) -> int:
"""A lower bound on the batch size of a new background update.
Used to ensure that progress is always made. Must be greater than 0.
"""
if self._min_batch_size_callback is not None:
return await self._min_batch_size_callback(update_name, database_name)
return self.minimum_background_batch_size
def get_current_update(self) -> Optional[BackgroundUpdatePerformance]:
"""Returns the current background update, if any."""
update_name = self._current_background_update
if not update_name:
return None
perf = self._background_update_performance.get(update_name)
if not perf:
perf = BackgroundUpdatePerformance(update_name)
return perf
def start_doing_background_updates(self) -> None:
if self.enabled:
# if we start a new background update, not all updates are done.
self._all_done = False
sleep = self.sleep_enabled
run_as_background_process(
"background_updates", self.run_background_updates, sleep
)
async def run_background_updates(self, sleep: bool) -> None:
if self._running or not self.enabled:
return
self._running = True
back_to_back_failures = 0
try:
logger.info(
"Starting background schema updates for database %s",
self._database_name,
)
while self.enabled:
try:
result = await self.do_next_background_update(sleep)
back_to_back_failures = 0
except Exception:
back_to_back_failures += 1
if back_to_back_failures >= 5:
raise RuntimeError(
"5 back-to-back background update failures; aborting."
)
logger.exception("Error doing update")
else:
if result:
logger.info(
"No more background updates to do."
" Unscheduling background update task."
)
self._all_done = True
return None
finally:
self._running = False
async def has_completed_background_updates(self) -> bool:
"""Check if all the background updates have completed
Returns:
True if all background updates have completed
"""
# if we've previously determined that there is nothing left to do, that
# is easy
if self._all_done:
return True
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# obviously, if we are currently processing an update, we're not done.
if self._current_background_update:
return False
# otherwise, check if there are updates to be run. This is important,
# as we may be running on a worker which doesn't perform the bg updates
# itself, but still wants to wait for them to happen.
updates = await self.db_pool.simple_select_onecol(
"background_updates",
keyvalues=None,
retcol="1",
desc="has_completed_background_updates",
)
if not updates:
self._all_done = True
return True
return False
async def has_completed_background_update(self, update_name: str) -> bool:
"""Check if the given background update has finished running."""
if self._all_done:
return True
if update_name == self._current_background_update:
return False
update_exists = await self.db_pool.simple_select_one_onecol(
"background_updates",
keyvalues={"update_name": update_name},
retcol="1",
desc="has_completed_background_update",
allow_none=True,
)
return not update_exists
async def do_next_background_update(self, sleep: bool = True) -> bool:
"""Does some amount of work on the next queued background update
Returns once some amount of work is done.
Args:
sleep: Whether to limit how quickly we run background updates or
not.
Returns:
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True if we have finished running all the background updates, otherwise False
"""
def get_background_updates_txn(txn: Cursor) -> List[Dict[str, Any]]:
txn.execute(
"""
SELECT update_name, depends_on FROM background_updates
ORDER BY ordering, update_name
"""
)
return self.db_pool.cursor_to_dict(txn)
if not self._current_background_update:
all_pending_updates = await self.db_pool.runInteraction(
"background_updates",
get_background_updates_txn,
)
if not all_pending_updates:
# no work left to do
return True
# find the first update which isn't dependent on another one in the queue.
pending = {update["update_name"] for update in all_pending_updates}
for upd in all_pending_updates:
depends_on = upd["depends_on"]
if not depends_on or depends_on not in pending:
break
logger.info(
"Not starting on bg update %s until %s is done",
upd["update_name"],
depends_on,
)
else:
# if we get to the end of that for loop, there is a problem
raise Exception(
"Unable to find a background update which doesn't depend on "
"another: dependency cycle?"
)
self._current_background_update = upd["update_name"]
# We have a background update to run, otherwise we would have returned
# early.
assert self._current_background_update is not None
update_info = self._background_update_handlers[self._current_background_update]
async with self._get_context_manager_for_update(
sleep=sleep,
update_name=self._current_background_update,
database_name=self._database_name,
oneshot=update_info.oneshot,
) as desired_duration_ms:
await self._do_background_update(desired_duration_ms)
return False
async def _do_background_update(self, desired_duration_ms: float) -> int:
assert self._current_background_update is not None
update_name = self._current_background_update
logger.info("Starting update batch on background update '%s'", update_name)
update_handler = self._background_update_handlers[update_name].callback
performance = self._background_update_performance.get(update_name)
if performance is None:
performance = BackgroundUpdatePerformance(update_name)
self._background_update_performance[update_name] = performance
items_per_ms = performance.average_items_per_ms()
if items_per_ms is not None:
batch_size = int(desired_duration_ms * items_per_ms)
# Clamp the batch size so that we always make progress
batch_size = max(
batch_size,
await self._min_batch_size(update_name, self._database_name),
)
else:
batch_size = await self._default_batch_size(
update_name, self._database_name
)
progress_json = await self.db_pool.simple_select_one_onecol(
"background_updates",
keyvalues={"update_name": update_name},
retcol="progress_json",
)
# Avoid a circular import.
from synapse.storage._base import db_to_json
progress = db_to_json(progress_json)
time_start = self._clock.time_msec()
items_updated = await update_handler(progress, batch_size)
time_stop = self._clock.time_msec()
duration_ms = time_stop - time_start
performance.update(items_updated, duration_ms)
logger.info(
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"Running background update %r. Processed %r items in %rms."
" (total_rate=%r/ms, current_rate=%r/ms, total_updated=%r, batch_size=%r)",
update_name,
items_updated,
duration_ms,
performance.total_items_per_ms(),
performance.average_items_per_ms(),
performance.total_item_count,
batch_size,
)
return len(self._background_update_performance)
def register_background_update_handler(
self,
update_name: str,
update_handler: Callable[[JsonDict, int], Awaitable[int]],
) -> None:
"""Register a handler for doing a background update.
The handler should take two arguments:
* A dict of the current progress
* An integer count of the number of items to update in this batch.
The handler should return a deferred or coroutine which returns an integer count
of items updated.
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The handler is responsible for updating the progress of the update.
Args:
update_name: The name of the update that this code handles.
update_handler: The function that does the update.
"""
self._background_update_handlers[update_name] = _BackgroundUpdateHandler(
update_handler
)
def register_background_index_update(
self,
update_name: str,
index_name: str,
table: str,
columns: Iterable[str],
where_clause: Optional[str] = None,
unique: bool = False,
psql_only: bool = False,
replaces_index: Optional[str] = None,
) -> None:
"""Helper for store classes to do a background index addition
To use:
1. use a schema delta file to add a background update. Example:
INSERT INTO background_updates (update_name, progress_json) VALUES
('my_new_index', '{}');
2. In the Store constructor, call this method
Args:
update_name: update_name to register for
index_name: name of index to add
table: table to add index to
columns: columns/expressions to include in index
where_clause: A WHERE clause to specify a partial unique index.
unique: true to make a UNIQUE index
psql_only: true to only create this index on psql databases (useful
for virtual sqlite tables)
replaces_index: The name of an index that this index replaces.
The named index will be dropped upon completion of the new index.
"""
async def updater(progress: JsonDict, batch_size: int) -> int:
await self.create_index_in_background(
index_name=index_name,
table=table,
columns=columns,
where_clause=where_clause,
unique=unique,
psql_only=psql_only,
replaces_index=replaces_index,
)
await self._end_background_update(update_name)
return 1
self._background_update_handlers[update_name] = _BackgroundUpdateHandler(
updater, oneshot=True
)
async def create_index_in_background(
self,
index_name: str,
table: str,
columns: Iterable[str],
where_clause: Optional[str] = None,
unique: bool = False,
psql_only: bool = False,
replaces_index: Optional[str] = None,
) -> None:
"""Add an index in the background.
Args:
update_name: update_name to register for
index_name: name of index to add
table: table to add index to
columns: columns/expressions to include in index
where_clause: A WHERE clause to specify a partial unique index.
unique: true to make a UNIQUE index
psql_only: true to only create this index on psql databases (useful
for virtual sqlite tables)
replaces_index: The name of an index that this index replaces.
The named index will be dropped upon completion of the new index.
"""
def create_index_psql(conn: Connection) -> None:
conn.rollback()
# postgres insists on autocommit for the index
conn.set_session(autocommit=True) # type: ignore
try:
c = conn.cursor()
# If a previous attempt to create the index was interrupted,
# we may already have a half-built index. Let's just drop it
# before trying to create it again.
sql = "DROP INDEX IF EXISTS %s" % (index_name,)
logger.debug("[SQL] %s", sql)
c.execute(sql)
sql = (
"CREATE %(unique)s INDEX CONCURRENTLY %(name)s"
" ON %(table)s"
" (%(columns)s) %(where_clause)s"
) % {
"unique": "UNIQUE" if unique else "",
"name": index_name,
"table": table,
"columns": ", ".join(columns),
"where_clause": "WHERE " + where_clause if where_clause else "",
}
logger.debug("[SQL] %s", sql)
c.execute(sql)
if replaces_index is not None:
# We drop the old index as the new index has now been created.
sql = f"DROP INDEX IF EXISTS {replaces_index}"
logger.debug("[SQL] %s", sql)
c.execute(sql)
finally:
conn.set_session(autocommit=False) # type: ignore
def create_index_sqlite(conn: Connection) -> None:
# Sqlite doesn't support concurrent creation of indexes.
#
# We assume that sqlite doesn't give us invalid indices; however
# we may still end up with the index existing but the
# background_updates not having been recorded if synapse got shut
# down at the wrong moment - hance we use IF NOT EXISTS. (SQLite
# has supported CREATE TABLE|INDEX IF NOT EXISTS since 3.3.0.)
sql = (
"CREATE %(unique)s INDEX IF NOT EXISTS %(name)s ON %(table)s"
" (%(columns)s) %(where_clause)s"
) % {
"unique": "UNIQUE" if unique else "",
"name": index_name,
"table": table,
"columns": ", ".join(columns),
"where_clause": "WHERE " + where_clause if where_clause else "",
}
c = conn.cursor()
logger.debug("[SQL] %s", sql)
c.execute(sql)
if replaces_index is not None:
# We drop the old index as the new index has now been created.
sql = f"DROP INDEX IF EXISTS {replaces_index}"
logger.debug("[SQL] %s", sql)
c.execute(sql)
if isinstance(self.db_pool.engine, engines.PostgresEngine):
runner: Optional[Callable[[Connection], None]] = create_index_psql
elif psql_only:
runner = None
else:
runner = create_index_sqlite
if runner is None:
return
logger.info("Adding index %s to %s", index_name, table)
await self.db_pool.runWithConnection(runner)
async def _end_background_update(self, update_name: str) -> None:
"""Removes a completed background update task from the queue.
Args:
update_name:: The name of the completed task to remove
Returns:
None, completes once the task is removed.
"""
if update_name != self._current_background_update:
raise Exception(
"Cannot end background update %s which isn't currently running"
% update_name
)
self._current_background_update = None
await self.db_pool.simple_delete_one(
"background_updates", keyvalues={"update_name": update_name}
)
async def _background_update_progress(
self, update_name: str, progress: dict
) -> None:
"""Update the progress of a background update
Args:
update_name: The name of the background update task
progress: The progress of the update.
"""
await self.db_pool.runInteraction(
"background_update_progress",
self._background_update_progress_txn,
update_name,
progress,
)
def _background_update_progress_txn(
self, txn: "LoggingTransaction", update_name: str, progress: JsonDict
) -> None:
"""Update the progress of a background update
Args:
txn: The transaction.
update_name: The name of the background update task
progress: The progress of the update.
"""
progress_json = json_encoder.encode(progress)
self.db_pool.simple_update_one_txn(
txn,
"background_updates",
keyvalues={"update_name": update_name},
updatevalues={"progress_json": progress_json},
)