summary refs log tree commit diff
path: root/synapse/storage/background_updates.py
blob: f43463df53b8b26612f2844c8ccf492b472f4dc4 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
# -*- coding: utf-8 -*-
# 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.

import logging
from typing import Optional

from canonicaljson import json

from twisted.internet import defer

from synapse.metrics.background_process_metrics import run_as_background_process

from . import engines

logger = logging.getLogger(__name__)


class BackgroundUpdatePerformance(object):
    """Tracks the how long a background update is taking to update its items"""

    def __init__(self, name):
        self.name = name
        self.total_item_count = 0
        self.total_duration_ms = 0
        self.avg_item_count = 0
        self.avg_duration_ms = 0

    def update(self, item_count, duration_ms):
        """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):
        """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):
        """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)


class BackgroundUpdater(object):
    """ 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, database):
        self._clock = hs.get_clock()
        self.db_pool = database

        # if a background update is currently running, its name.
        self._current_background_update = None  # type: Optional[str]

        self._background_update_performance = {}
        self._background_update_handlers = {}
        self._all_done = False

    def start_doing_background_updates(self):
        run_as_background_process("background_updates", self.run_background_updates)

    async def run_background_updates(self, sleep=True):
        logger.info("Starting background schema updates")
        while True:
            if sleep:
                await self._clock.sleep(self.BACKGROUND_UPDATE_INTERVAL_MS / 1000.0)

            try:
                result = await self.do_next_background_update(
                    self.BACKGROUND_UPDATE_DURATION_MS
                )
            except Exception:
                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

        # 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) -> 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(float): How long we want to spend
                updating.
        Returns:
            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:
        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(
            "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, update_handler):
        """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.

        The handler is responsible for updating the progress of the update.

        Args:
            update_name(str): The name of the update that this code handles.
            update_handler(function): The function that does the update.
        """
        self._background_update_handlers[update_name] = update_handler

    def register_noop_background_update(self, update_name):
        """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 (str): Name of update
        """

        @defer.inlineCallbacks
        def noop_update(progress, batch_size):
            yield 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,
        index_name,
        table,
        columns,
        where_clause=None,
        unique=False,
        psql_only=False,
    ):
        """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 (str): update_name to register for
            index_name (str): name of index to add
            table (str): table to add index to
            columns (list[str]): columns/expressions to include in index
            unique (bool): 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):
            conn.rollback()
            # postgres insists on autocommit for the index
            conn.set_session(autocommit=True)

            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)

        def create_index_sqlite(conn):
            # 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 = create_index_psql
        elif psql_only:
            runner = None
        else:
            runner = create_index_sqlite

        @defer.inlineCallbacks
        def updater(progress, batch_size):
            if runner is not None:
                logger.info("Adding index %s to %s", index_name, table)
                yield self.db_pool.runWithConnection(runner)
            yield self._end_background_update(update_name)
            return 1

        self.register_background_update_handler(update_name, updater)

    def _end_background_update(self, update_name):
        """Removes a completed background update task from the queue.

        Args:
            update_name(str): The name of the completed task to remove
        Returns:
            A deferred that 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
        return self.db_pool.simple_delete_one(
            "background_updates", keyvalues={"update_name": update_name}
        )

    def _background_update_progress(self, update_name: str, progress: dict):
        """Update the progress of a background update

        Args:
            update_name: The name of the background update task
            progress: The progress of the update.
        """

        return self.db_pool.runInteraction(
            "background_update_progress",
            self._background_update_progress_txn,
            update_name,
            progress,
        )

    def _background_update_progress_txn(self, txn, update_name, progress):
        """Update the progress of a background update

        Args:
            txn(cursor): The transaction.
            update_name(str): The name of the background update task
            progress(dict): The progress of the update.
        """

        progress_json = json.dumps(progress)

        self.db_pool.simple_update_one_txn(
            txn,
            "background_updates",
            keyvalues={"update_name": update_name},
            updatevalues={"progress_json": progress_json},
        )