468 lines
17 KiB
Python
468 lines
17 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2014-2016 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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from typing import Optional
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from synapse.metrics.background_process_metrics import run_as_background_process
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from synapse.util import json_encoder
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from . import engines
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logger = logging.getLogger(__name__)
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class BackgroundUpdatePerformance:
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"""Tracks the how long a background update is taking to update its items"""
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def __init__(self, name):
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self.name = name
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self.total_item_count = 0
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self.total_duration_ms = 0
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self.avg_item_count = 0
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self.avg_duration_ms = 0
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def update(self, item_count, duration_ms):
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"""Update the stats after doing an update"""
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self.total_item_count += item_count
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self.total_duration_ms += duration_ms
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# Exponential moving averages for the number of items updated and
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# the duration.
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self.avg_item_count += 0.1 * (item_count - self.avg_item_count)
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self.avg_duration_ms += 0.1 * (duration_ms - self.avg_duration_ms)
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def average_items_per_ms(self):
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"""An estimate of how long it takes to do a single update.
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Returns:
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A duration in ms as a float
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"""
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if self.avg_duration_ms == 0:
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return 0
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elif self.total_item_count == 0:
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return None
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else:
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# Use the exponential moving average so that we can adapt to
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# changes in how long the update process takes.
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return float(self.avg_item_count) / float(self.avg_duration_ms)
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def total_items_per_ms(self):
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"""An estimate of how long it takes to do a single update.
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Returns:
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A duration in ms as a float
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"""
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if self.total_duration_ms == 0:
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return 0
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elif self.total_item_count == 0:
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return None
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else:
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return float(self.total_item_count) / float(self.total_duration_ms)
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class BackgroundUpdater:
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""" Background updates are updates to the database that run in the
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background. Each update processes a batch of data at once. We attempt to
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limit the impact of each update by monitoring how long each batch takes to
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process and autotuning the batch size.
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"""
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MINIMUM_BACKGROUND_BATCH_SIZE = 100
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DEFAULT_BACKGROUND_BATCH_SIZE = 100
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BACKGROUND_UPDATE_INTERVAL_MS = 1000
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BACKGROUND_UPDATE_DURATION_MS = 100
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def __init__(self, hs, database):
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self._clock = hs.get_clock()
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self.db_pool = database
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# if a background update is currently running, its name.
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self._current_background_update = None # type: Optional[str]
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self._background_update_performance = {}
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self._background_update_handlers = {}
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self._all_done = False
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def start_doing_background_updates(self):
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run_as_background_process("background_updates", self.run_background_updates)
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async def run_background_updates(self, sleep=True):
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logger.info("Starting background schema updates")
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while True:
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if sleep:
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await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)
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try:
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result = await self.do_next_background_update(
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self.BACKGROUND_UPDATE_DURATION_MS
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)
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except Exception:
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logger.exception("Error doing update")
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else:
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if result:
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logger.info(
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"No more background updates to do."
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" Unscheduling background update task."
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)
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self._all_done = True
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return None
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async def has_completed_background_updates(self) -> bool:
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"""Check if all the background updates have completed
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Returns:
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True if all background updates have completed
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"""
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# if we've previously determined that there is nothing left to do, that
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# is easy
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if self._all_done:
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return True
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# obviously, if we are currently processing an update, we're not done.
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if self._current_background_update:
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return False
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# otherwise, check if there are updates to be run. This is important,
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# as we may be running on a worker which doesn't perform the bg updates
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# itself, but still wants to wait for them to happen.
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updates = await self.db_pool.simple_select_onecol(
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"background_updates",
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keyvalues=None,
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retcol="1",
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desc="has_completed_background_updates",
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)
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if not updates:
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self._all_done = True
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return True
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return False
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async def has_completed_background_update(self, update_name) -> bool:
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"""Check if the given background update has finished running.
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"""
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if self._all_done:
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return True
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if update_name == self._current_background_update:
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return False
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update_exists = await self.db_pool.simple_select_one_onecol(
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"background_updates",
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keyvalues={"update_name": update_name},
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retcol="1",
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desc="has_completed_background_update",
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allow_none=True,
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)
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return not update_exists
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async def do_next_background_update(self, desired_duration_ms: float) -> bool:
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"""Does some amount of work on the next queued background update
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Returns once some amount of work is done.
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Args:
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desired_duration_ms(float): How long we want to spend
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updating.
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Returns:
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True if we have finished running all the background updates, otherwise False
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"""
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def get_background_updates_txn(txn):
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txn.execute(
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"""
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SELECT update_name, depends_on FROM background_updates
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ORDER BY ordering, update_name
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"""
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)
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return self.db_pool.cursor_to_dict(txn)
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if not self._current_background_update:
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all_pending_updates = await self.db_pool.runInteraction(
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"background_updates", get_background_updates_txn,
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)
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if not all_pending_updates:
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# no work left to do
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return True
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# find the first update which isn't dependent on another one in the queue.
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pending = {update["update_name"] for update in all_pending_updates}
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for upd in all_pending_updates:
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depends_on = upd["depends_on"]
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if not depends_on or depends_on not in pending:
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break
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logger.info(
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"Not starting on bg update %s until %s is done",
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upd["update_name"],
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depends_on,
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)
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else:
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# if we get to the end of that for loop, there is a problem
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raise Exception(
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"Unable to find a background update which doesn't depend on "
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"another: dependency cycle?"
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)
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self._current_background_update = upd["update_name"]
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await self._do_background_update(desired_duration_ms)
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return False
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async def _do_background_update(self, desired_duration_ms: float) -> int:
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update_name = self._current_background_update
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logger.info("Starting update batch on background update '%s'", update_name)
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update_handler = self._background_update_handlers[update_name]
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performance = self._background_update_performance.get(update_name)
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if performance is None:
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performance = BackgroundUpdatePerformance(update_name)
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self._background_update_performance[update_name] = performance
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items_per_ms = performance.average_items_per_ms()
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if items_per_ms is not None:
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batch_size = int(desired_duration_ms * items_per_ms)
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# Clamp the batch size so that we always make progress
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batch_size = max(batch_size, self.MINIMUM_BACKGROUND_BATCH_SIZE)
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else:
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batch_size = self.DEFAULT_BACKGROUND_BATCH_SIZE
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progress_json = await self.db_pool.simple_select_one_onecol(
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"background_updates",
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keyvalues={"update_name": update_name},
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retcol="progress_json",
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)
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# Avoid a circular import.
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from synapse.storage._base import db_to_json
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progress = db_to_json(progress_json)
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time_start = self._clock.time_msec()
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items_updated = await update_handler(progress, batch_size)
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time_stop = self._clock.time_msec()
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duration_ms = time_stop - time_start
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logger.info(
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"Running background update %r. Processed %r items in %rms."
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" (total_rate=%r/ms, current_rate=%r/ms, total_updated=%r, batch_size=%r)",
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update_name,
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items_updated,
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duration_ms,
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performance.total_items_per_ms(),
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performance.average_items_per_ms(),
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performance.total_item_count,
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batch_size,
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)
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performance.update(items_updated, duration_ms)
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return len(self._background_update_performance)
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def register_background_update_handler(self, update_name, update_handler):
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"""Register a handler for doing a background update.
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The handler should take two arguments:
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* A dict of the current progress
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* An integer count of the number of items to update in this batch.
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The handler should return a deferred or coroutine which returns an integer count
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of items updated.
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The handler is responsible for updating the progress of the update.
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Args:
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update_name(str): The name of the update that this code handles.
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update_handler(function): The function that does the update.
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"""
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self._background_update_handlers[update_name] = update_handler
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def register_noop_background_update(self, update_name):
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"""Register a noop handler for a background update.
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This is useful when we previously did a background update, but no
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longer wish to do the update. In this case the background update should
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be removed from the schema delta files, but there may still be some
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users who have the background update queued, so this method should
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also be called to clear the update.
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Args:
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update_name (str): Name of update
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"""
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async def noop_update(progress, batch_size):
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await self._end_background_update(update_name)
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return 1
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self.register_background_update_handler(update_name, noop_update)
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def register_background_index_update(
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self,
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update_name,
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index_name,
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table,
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columns,
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where_clause=None,
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unique=False,
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psql_only=False,
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):
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"""Helper for store classes to do a background index addition
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To use:
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1. use a schema delta file to add a background update. Example:
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INSERT INTO background_updates (update_name, progress_json) VALUES
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('my_new_index', '{}');
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2. In the Store constructor, call this method
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Args:
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update_name (str): update_name to register for
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index_name (str): name of index to add
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table (str): table to add index to
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columns (list[str]): columns/expressions to include in index
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unique (bool): true to make a UNIQUE index
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psql_only: true to only create this index on psql databases (useful
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for virtual sqlite tables)
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"""
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def create_index_psql(conn):
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conn.rollback()
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# postgres insists on autocommit for the index
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conn.set_session(autocommit=True)
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try:
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c = conn.cursor()
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# If a previous attempt to create the index was interrupted,
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# we may already have a half-built index. Let's just drop it
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# before trying to create it again.
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sql = "DROP INDEX IF EXISTS %s" % (index_name,)
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logger.debug("[SQL] %s", sql)
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c.execute(sql)
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sql = (
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"CREATE %(unique)s INDEX CONCURRENTLY %(name)s"
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" ON %(table)s"
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" (%(columns)s) %(where_clause)s"
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) % {
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"unique": "UNIQUE" if unique else "",
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"name": index_name,
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"table": table,
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"columns": ", ".join(columns),
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"where_clause": "WHERE " + where_clause if where_clause else "",
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}
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logger.debug("[SQL] %s", sql)
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c.execute(sql)
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finally:
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conn.set_session(autocommit=False)
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def create_index_sqlite(conn):
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# Sqlite doesn't support concurrent creation of indexes.
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#
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# We don't use partial indices on SQLite as it wasn't introduced
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# until 3.8, and wheezy and CentOS 7 have 3.7
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#
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# We assume that sqlite doesn't give us invalid indices; however
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# we may still end up with the index existing but the
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# background_updates not having been recorded if synapse got shut
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# down at the wrong moment - hance we use IF NOT EXISTS. (SQLite
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# has supported CREATE TABLE|INDEX IF NOT EXISTS since 3.3.0.)
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sql = (
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"CREATE %(unique)s INDEX IF NOT EXISTS %(name)s ON %(table)s"
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" (%(columns)s)"
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) % {
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"unique": "UNIQUE" if unique else "",
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"name": index_name,
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"table": table,
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"columns": ", ".join(columns),
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}
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c = conn.cursor()
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logger.debug("[SQL] %s", sql)
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c.execute(sql)
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if isinstance(self.db_pool.engine, engines.PostgresEngine):
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runner = create_index_psql
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elif psql_only:
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runner = None
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else:
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runner = create_index_sqlite
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async def updater(progress, batch_size):
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if runner is not None:
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logger.info("Adding index %s to %s", index_name, table)
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await self.db_pool.runWithConnection(runner)
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await self._end_background_update(update_name)
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return 1
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self.register_background_update_handler(update_name, updater)
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async def _end_background_update(self, update_name: str) -> None:
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"""Removes a completed background update task from the queue.
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Args:
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update_name:: The name of the completed task to remove
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Returns:
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None, completes once the task is removed.
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"""
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if update_name != self._current_background_update:
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raise Exception(
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"Cannot end background update %s which isn't currently running"
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% update_name
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)
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self._current_background_update = None
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await self.db_pool.simple_delete_one(
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"background_updates", keyvalues={"update_name": update_name}
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)
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async def _background_update_progress(self, update_name: str, progress: dict):
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"""Update the progress of a background update
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Args:
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update_name: The name of the background update task
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progress: The progress of the update.
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"""
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return await self.db_pool.runInteraction(
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"background_update_progress",
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self._background_update_progress_txn,
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update_name,
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progress,
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)
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def _background_update_progress_txn(self, txn, update_name, progress):
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"""Update the progress of a background update
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Args:
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txn(cursor): The transaction.
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update_name(str): The name of the background update task
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progress(dict): The progress of the update.
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"""
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progress_json = json_encoder.encode(progress)
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self.db_pool.simple_update_one_txn(
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txn,
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"background_updates",
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keyvalues={"update_name": update_name},
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updatevalues={"progress_json": progress_json},
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)
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