forked-synapse/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 typing import TYPE_CHECKING, Awaitable, Callable, Dict, Iterable, Optional
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.storage.types import Connection
from synapse.types import JsonDict
from synapse.util import 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__)
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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
"""
if self.avg_duration_ms == 0:
return 0
elif self.total_item_count == 0:
return None
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.
"""
MINIMUM_BACKGROUND_BATCH_SIZE = 100
DEFAULT_BACKGROUND_BATCH_SIZE = 100
BACKGROUND_UPDATE_INTERVAL_MS = 1000
BACKGROUND_UPDATE_DURATION_MS = 100
def __init__(self, hs: "HomeServer", database: "DatabasePool"):
self._clock = hs.get_clock()
self.db_pool = database
# if a background update is currently running, its name.
self._current_background_update: Optional[str] = None
self._background_update_performance: Dict[str, BackgroundUpdatePerformance] = {}
self._background_update_handlers: Dict[
str, Callable[[JsonDict, int], Awaitable[int]]
] = {}
self._all_done = False
def start_doing_background_updates(self) -> None:
run_as_background_process("background_updates", self.run_background_updates)
async def run_background_updates(self, sleep: bool = True) -> None:
logger.info("Starting background schema updates")
while True:
if sleep:
await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)
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try:
result = await self.do_next_background_update(
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self.BACKGROUND_UPDATE_DURATION_MS
)
except Exception:
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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
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, desired_duration_ms: float) -> bool:
"""Does some amount of work on the next queued background update
Returns once some amount of work is done.
Args:
desired_duration_ms: How long we want to spend updating.
Returns:
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True if we have finished running all the background updates, otherwise False
"""
def get_background_updates_txn(txn):
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"]
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]
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, self.MINIMUM_BACKGROUND_BATCH_SIZE)
else:
batch_size = self.DEFAULT_BACKGROUND_BATCH_SIZE
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
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,
)
performance.update(items_updated, duration_ms)
return len(self._background_update_performance)
def register_background_update_handler(
self,
update_name: str,
update_handler: Callable[[JsonDict, int], Awaitable[int]],
):
"""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] = update_handler
def register_noop_background_update(self, update_name: str) -> None:
"""Register a noop handler for a background update.
This is useful when we previously did a background update, but no
longer wish to do the update. In this case the background update should
be removed from the schema delta files, but there may still be some
users who have the background update queued, so this method should
also be called to clear the update.
Args:
update_name: Name of update
"""
async def noop_update(progress: JsonDict, batch_size: int) -> int:
await self._end_background_update(update_name)
return 1
self.register_background_update_handler(update_name, noop_update)
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,
) -> 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
unique: true to make a UNIQUE index
psql_only: true to only create this index on psql databases (useful
for virtual sqlite tables)
"""
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)
finally:
conn.set_session(autocommit=False) # type: ignore
def create_index_sqlite(conn: Connection) -> None:
# Sqlite doesn't support concurrent creation of indexes.
#
# We don't use partial indices on SQLite as it wasn't introduced
# until 3.8, and wheezy and CentOS 7 have 3.7
#
# 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)"
) % {
"unique": "UNIQUE" if unique else "",
"name": index_name,
"table": table,
"columns": ", ".join(columns),
}
c = conn.cursor()
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
async def updater(progress, batch_size):
if runner is not None:
logger.info("Adding index %s to %s", index_name, table)
await self.db_pool.runWithConnection(runner)
await self._end_background_update(update_name)
return 1
self.register_background_update_handler(update_name, updater)
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},
)