sqlite.py 28.5 KB
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721
#
# Copyright (C) 2012-2017  Nexedi SA
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

from collections import OrderedDict
import os
import sqlite3
from hashlib import sha1
import string
import traceback

from . import LOG_QUERIES
from .manager import DatabaseManager, splitOIDField
from neo.lib import logging, util
from neo.lib.interfaces import implements
from neo.lib.protocol import CellStates, ZERO_OID, ZERO_TID, ZERO_HASH

def unique_constraint_message(table, *columns):
    c = sqlite3.connect(":memory:")
    values = '?' * len(columns)
    insert = "INSERT INTO %s VALUES(%s)" % (table, ', '.join(values))
    x = "%s (%s)" % (table, ', '.join(columns))
    c.execute("CREATE TABLE " + x)
    c.execute("CREATE UNIQUE INDEX i ON " + x)
    try:
        c.executemany(insert, (values, values))
    except sqlite3.IntegrityError, e:
        return e.args[0]
    assert False

def retry_if_locked(f, *args):
    try:
        return f(*args)
    except sqlite3.OperationalError as e:
        x = e.args[0]
        if x != 'database is locked':
            raise
        msg = traceback.format_exception_only(type(e), e)
        msg += traceback.format_stack()
        logging.warning(''.join(msg))
        while 1:
            try:
                return f(*args)
            except sqlite3.OperationalError as e:
                if e.args[0] != x:
                    raise


@implements
class SQLiteDatabaseManager(DatabaseManager):
    """This class manages a database on SQLite.

    CAUTION: Make sure we never use statement journal files, as explained at
             https://www.sqlite.org/tempfiles.html for more information.
             In other words, temporary files (by default in /var/tmp !) must
             never be used for small requests.
    """

    VERSION = 2

    def _parse(self, database):
        self.db = os.path.expanduser(database)

    def _close(self):
        self.conn.close()

    def _connect(self):
        logging.info('connecting to SQLite database %r', self.db)
        self.conn = sqlite3.connect(self.db, check_same_thread=False)
        self.lock(self.db)
        if self.UNSAFE:
            q = self.query
            q("PRAGMA synchronous = OFF")
            q("PRAGMA journal_mode = MEMORY")
        self._config = {}

    def _commit(self):
        retry_if_locked(self.conn.commit)

    if LOG_QUERIES:
        def query(self, query):
            printable_char_list = []
            for c in query.split('\n', 1)[0][:70]:
                if c not in string.printable or c in '\t\x0b\x0c\r':
                    c = '\\x%02x' % ord(c)
                printable_char_list.append(c)
            logging.debug('querying %s...', ''.join(printable_char_list))
            return self.conn.execute(query)
    else:
        query = property(lambda self: self.conn.execute)

    def erase(self):
        for t in 'config', 'pt', 'trans', 'obj', 'data', 'ttrans', 'tobj':
            self.query('DROP TABLE IF EXISTS ' + t)

    def nonempty(self, table):
        try:
            return bool(self.query(
                "SELECT 1 FROM %s LIMIT 1" % table).fetchone())
        except sqlite3.OperationalError as e:
            if not e.args[0].startswith("no such table:"):
                raise

    def _alterTable(self, schema_dict, table, select="*"):
        # BBB: As explained in _setup, no transactional DDL
        #      so let's do the same dance as for MySQL.
        q = self.query
        new = 'new_' + table
        if self.nonempty(table) is None:
            if self.nonempty(new) is None:
                return
        else:
            q("DROP TABLE IF EXISTS " + new)
            q(schema_dict.pop(table) % new)
            q("INSERT INTO %s SELECT %s FROM %s" % (new, select, table))
            q("DROP TABLE " + table)
        q("ALTER TABLE %s RENAME TO %s" % (new, table))

    def _migrate1(self, *_):
        self._checkNoUnfinishedTransactions()
        self.query("DROP TABLE IF EXISTS ttrans")

    def _migrate2(self, schema_dict, index_dict):
        self._alterTable(schema_dict, 'obj')

    def _setup(self, dedup=False):
        # BBB: SQLite has transactional DDL but before Python 3.6,
        #      the binding automatically commits between such statements.
        #      This anti-feature causes this method to be relatively slow.
        #      Unit tests enables the UNSAFE boolean flag.
        self._config.clear()
        q = self.query
        schema_dict = OrderedDict()
        index_dict = {}

        # The table "config" stores configuration
        # parameters which affect the persistent data.
        schema_dict['config'] = """CREATE TABLE %s (
                 name TEXT NOT NULL PRIMARY KEY,
                 value TEXT)
            """

        # The table "pt" stores a partition table.
        schema_dict['pt'] = """CREATE TABLE %s (
                 rid INTEGER NOT NULL,
                 nid INTEGER NOT NULL,
                 state INTEGER NOT NULL,
                 PRIMARY KEY (rid, nid))
            """

        # The table "trans" stores information on committed transactions.
        schema_dict['trans'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 packed BOOLEAN NOT NULL,
                 oids BLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid INTEGER NOT NULL,
                 PRIMARY KEY (partition, tid))
            """

        # The table "obj" stores committed object metadata.
        schema_dict['obj'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 oid INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 data_id INTEGER,
                 value_tid INTEGER,
                 PRIMARY KEY (partition, oid, tid))
            """
        index_dict['obj'] = (
            "CREATE INDEX %s ON %s(partition, tid, oid)",
            "CREATE INDEX %s ON %s(data_id)")

        # The table "data" stores object data.
        schema_dict['data'] = """CREATE TABLE %s (
                 id INTEGER PRIMARY KEY,
                 hash BLOB NOT NULL,
                 compression INTEGER NOT NULL,
                 value BLOB NOT NULL)
            """
        if dedup:
            index_dict['data'] = (
                "CREATE UNIQUE INDEX %s ON %s(hash, compression)",)

        # The table "ttrans" stores information on uncommitted transactions.
        schema_dict['ttrans'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 tid INTEGER,
                 packed BOOLEAN NOT NULL,
                 oids BLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid INTEGER NOT NULL)
            """

        # The table "tobj" stores uncommitted object metadata.
        schema_dict['tobj'] = """CREATE TABLE %s (
                 partition INTEGER NOT NULL,
                 oid INTEGER NOT NULL,
                 tid INTEGER NOT NULL,
                 data_id INTEGER,
                 value_tid INTEGER,
                 PRIMARY KEY (tid, oid))
            """

        if self.nonempty('config') is None:
            q(schema_dict.pop('config') % 'config')
            self._setConfiguration('version', self.VERSION)
        else:
            self.migrate(schema_dict, index_dict)

        for table, schema in schema_dict.iteritems():
            q(schema % ('IF NOT EXISTS ' + table))
        for table, index in index_dict.iteritems():
            for i, index in enumerate(index, 1):
                q(index % ('IF NOT EXISTS _%s_i%s' % (table, i), table))

        self._uncommitted_data.update(q("SELECT data_id, count(*)"
            " FROM tobj WHERE data_id IS NOT NULL GROUP BY data_id"))

    def getConfiguration(self, key):
        try:
            return self._config[key]
        except KeyError:
            try:
                r = self.query("SELECT value FROM config WHERE name=?",
                               (key,)).fetchone()[0]
            except TypeError:
                r = None
            self._config[key] = r
            return r

    def _setConfiguration(self, key, value):
        q = self.query
        self._config[key] = value
        if value is None:
            q("DELETE FROM config WHERE name=?", (key,))
        else:
            q("REPLACE INTO config VALUES (?,?)", (key, str(value)))

    def getPartitionTable(self, *nid):
        if nid:
            return self.query("SELECT rid, state FROM pt WHERE nid=?", nid)
        return self.query("SELECT * FROM pt")

    # A test with a table of 20 million lines and SQLite 3.8.7.1 shows that
    # it's not worth changing getLastTID:
    # - It already returns the result in less than 2 seconds, without reading
    #   the whole table (this is 4-7 times faster than MySQL).
    # - Strangely, a "GROUP BY partition" clause makes SQLite almost twice
    #   slower.
    # - Getting MAX(tid) is immediate with a "AND partition=?" condition so one
    #   way to speed up the following 2 methods is to repeat the queries for
    #   each partition (and finish in Python with max() for getLastTID).

    def getLastTID(self, max_tid):
        return self.query(
            "SELECT MAX(tid) FROM pt, trans"
            " WHERE nid=? AND rid=partition AND tid<=?",
            (self.getUUID(), max_tid,)).next()[0]

    def _getLastIDs(self):
        p64 = util.p64
        q = self.query
        args = self.getUUID(),
        trans = {partition: p64(tid)
            for partition, tid in q(
                "SELECT partition, MAX(tid) FROM pt, trans"
                " WHERE nid=? AND rid=partition GROUP BY partition", args)}
        obj = {partition: p64(tid)
            for partition, tid in q(
                "SELECT partition, MAX(tid) FROM pt, obj"
                " WHERE nid=? AND rid=partition GROUP BY partition", args)}
        oid = q("SELECT MAX(oid) oid FROM pt, obj"
                " WHERE nid=? AND rid=partition", args).next()[0]
        return trans, obj, None if oid is None else p64(oid)

    def _getDataLastId(self, partition):
        return self.query("SELECT MAX(id) FROM data WHERE %s <= id AND id < %s"
            % (partition << 48, (partition + 1) << 48)).fetchone()[0]

    def _getUnfinishedTIDDict(self):
        q = self.query
        return q("SELECT ttid, tid FROM ttrans"), (ttid
            for ttid, in q("SELECT DISTINCT tid FROM tobj"))

    def getFinalTID(self, ttid):
        ttid = util.u64(ttid)
        # As of SQLite 3.8.7.1, 'tid>=ttid' would ignore the index on tid,
        # even though ttid is a constant.
        for tid, in self.query("SELECT tid FROM trans"
                " WHERE partition=? AND tid>=? AND ttid=? LIMIT 1",
                (self._getReadablePartition(ttid), ttid, ttid)):
            return util.p64(tid)

    def getLastObjectTID(self, oid):
        oid = util.u64(oid)
        r = self.query("SELECT tid FROM obj"
                       " WHERE partition=? AND oid=?"
                       " ORDER BY tid DESC LIMIT 1",
                       (self._getReadablePartition(oid), oid)).fetchone()
        return r and util.p64(r[0])

    def _getNextTID(self, *args): # partition, oid, tid
        r = self.query("""SELECT tid FROM obj
                          WHERE partition=? AND oid=? AND tid>?
                          ORDER BY tid LIMIT 1""", args).fetchone()
        return r and r[0]

    def _getObject(self, oid, tid=None, before_tid=None):
        q = self.query
        partition = self._getReadablePartition(oid)
        sql = ('SELECT tid, compression, data.hash, value, value_tid'
               ' FROM obj LEFT JOIN data ON obj.data_id = data.id'
               ' WHERE partition=? AND oid=?')
        if tid is not None:
            r = q(sql + ' AND tid=?', (partition, oid, tid))
        elif before_tid is not None:
            r = q(sql + ' AND tid<? ORDER BY tid DESC LIMIT 1',
                  (partition, oid, before_tid))
        else:
            r = q(sql + ' ORDER BY tid DESC LIMIT 1', (partition, oid))
        try:
            serial, compression, checksum, data, value_serial = r.fetchone()
        except TypeError:
            return None
        if checksum:
            checksum = str(checksum)
            data = str(data)
        return (serial, self._getNextTID(partition, oid, serial),
                compression, checksum, data, value_serial)

    def _changePartitionTable(self, cell_list, reset=False):
        q = self.query
        if reset:
            q("DELETE FROM pt")
        for offset, nid, state in cell_list:
            # TODO: this logic should move out of database manager
            # add 'dropCells(cell_list)' to API and use one query
            # WKRD: Why does SQLite need a statement journal file
            #       whereas we try to replace only 1 value ?
            #       We don't want to remove the 'NOT NULL' constraint
            #       so we must simulate a "REPLACE OR FAIL".
            q("DELETE FROM pt WHERE rid=? AND nid=?", (offset, nid))
            if state != CellStates.DISCARDED:
                q("INSERT OR FAIL INTO pt VALUES (?,?,?)",
                  (offset, nid, int(state)))

    def dropPartitions(self, offset_list):
        where = " WHERE partition=?"
        q = self.query
        for partition in offset_list:
            args = partition,
            data_id_list = [x for x, in q(
                "SELECT DISTINCT data_id FROM obj%s AND data_id IS NOT NULL"
                % where, args)]
            q("DELETE FROM obj" + where, args)
            q("DELETE FROM trans" + where, args)
            self._pruneData(data_id_list)

    def _getUnfinishedDataIdList(self):
        return [x for x, in self.query(
            "SELECT data_id FROM tobj WHERE data_id IS NOT NULL")]

    def dropPartitionsTemporary(self, offset_list=None):
        where = "" if offset_list is None else \
            " WHERE `partition` IN (%s)" % ','.join(map(str, offset_list))
        q = self.query
        q("DELETE FROM tobj" + where)
        q("DELETE FROM ttrans" + where)

    def storeTransaction(self, tid, object_list, transaction, temporary=True):
        u64 = util.u64
        tid = u64(tid)
        T = 't' if temporary else ''
        obj_sql = "INSERT OR FAIL INTO %sobj VALUES (?,?,?,?,?)" % T
        q = self.query
        for oid, data_id, value_serial in object_list:
            oid = u64(oid)
            partition = self._getPartition(oid)
            if value_serial:
                value_serial = u64(value_serial)
                (data_id,), = q("SELECT data_id FROM obj"
                    " WHERE partition=? AND oid=? AND tid=?",
                    (partition, oid, value_serial))
                if temporary:
                    self.holdData(data_id)
            try:
                q(obj_sql, (partition, oid, tid, data_id, value_serial))
            except sqlite3.IntegrityError:
                # This may happen if a previous replication of 'obj' was
                # interrupted.
                if not T:
                    r, = q("SELECT data_id, value_tid FROM obj"
                           " WHERE partition=? AND oid=? AND tid=?",
                           (partition, oid, tid))
                    if r == (data_id, value_serial):
                        continue
                raise
        if transaction:
            oid_list, user, desc, ext, packed, ttid = transaction
            partition = self._getPartition(tid)
            assert packed in (0, 1)
            q("INSERT OR FAIL INTO %strans VALUES (?,?,?,?,?,?,?,?)" % T,
                (partition, None if temporary else tid,
                 packed, buffer(''.join(oid_list)),
                 buffer(user), buffer(desc), buffer(ext), u64(ttid)))

    def getOrphanList(self):
        return [x for x, in self.query(
            "SELECT id FROM data LEFT JOIN obj ON (id=data_id)"
            " WHERE data_id IS NULL")]

    def _pruneData(self, data_id_list):
        data_id_list = set(data_id_list).difference(self._uncommitted_data)
        if data_id_list:
            q = self.query
            data_id_list.difference_update(x for x, in q(
                "SELECT DISTINCT data_id FROM obj WHERE data_id IN (%s)"
                % ",".join(map(str, data_id_list))))
            q("DELETE FROM data WHERE id IN (%s)"
              % ",".join(map(str, data_id_list)))
            return len(data_id_list)
        return 0

    def storeData(self, checksum, oid, data, compression,
            _dup=unique_constraint_message("data", "hash", "compression")):
        H = buffer(checksum)
        p = self._getPartition(util.u64(oid))
        r = self._data_last_ids[p]
        try:
            self.query("INSERT INTO data VALUES (?,?,?,?)",
                (r, H, compression,  buffer(data)))
        except sqlite3.IntegrityError, e:
            if e.args[0] == _dup:
                (r, d), = self.query("SELECT id, value FROM data"
                                     " WHERE hash=? AND compression=?",
                                     (H, compression))
                if str(d) == data:
                    return r
            raise
        self._data_last_ids[p] = r + 1
        return r

    def loadData(self, data_id):
        return self.query("SELECT compression, hash, value"
                          " FROM data WHERE id=?", (data_id,)).fetchone()

    def _getDataTID(self, oid, tid=None, before_tid=None):
        partition = self._getReadablePartition(oid)
        sql = 'SELECT tid, value_tid FROM obj' \
              ' WHERE partition=? AND oid=?'
        if tid is not None:
            r = self.query(sql + ' AND tid=?', (partition, oid, tid))
        elif before_tid is not None:
            r = self.query(sql + ' AND tid<? ORDER BY tid DESC LIMIT 1',
                           (partition, oid, before_tid))
        else:
            r = self.query(sql + ' ORDER BY tid DESC LIMIT 1',
                           (partition, oid))
        r = r.fetchone()
        return r or (None, None)

    def lockTransaction(self, tid, ttid):
        u64 = util.u64
        self.query("UPDATE ttrans SET tid=? WHERE ttid=?",
                   (u64(tid), u64(ttid)))
        self.commit()

    def unlockTransaction(self, tid, ttid):
        q = self.query
        u64 = util.u64
        tid = u64(tid)
        ttid = u64(ttid)
        sql = " FROM tobj WHERE tid=?"
        data_id_list = [x for x, in q("SELECT data_id%s AND data_id IS NOT NULL"
                                      % sql, (ttid,))]
        q("INSERT INTO obj SELECT partition, oid, ?, data_id, value_tid" + sql,
          (tid, ttid))
        q("DELETE" + sql, (ttid,))
        q("INSERT INTO trans SELECT * FROM ttrans WHERE tid=?", (tid,))
        q("DELETE FROM ttrans WHERE tid=?", (tid,))
        self.releaseData(data_id_list)

    def abortTransaction(self, ttid):
        args = util.u64(ttid),
        q = self.query
        q("DELETE FROM tobj WHERE tid=?", args)
        q("DELETE FROM ttrans WHERE ttid=?", args)

    def deleteTransaction(self, tid):
        tid = util.u64(tid)
        self.query("DELETE FROM trans WHERE partition=? AND tid=?",
            (self._getPartition(tid), tid))

    def deleteObject(self, oid, serial=None):
        oid = util.u64(oid)
        sql = " FROM obj WHERE partition=? AND oid=?"
        args = [self._getPartition(oid), oid]
        if serial:
            sql += " AND tid=?"
            args.append(util.u64(serial))
        q = self.query
        data_id_list = [x for x, in q(
            "SELECT DISTINCT data_id%s AND data_id IS NOT NULL" % sql, args)]
        q("DELETE" + sql, args)
        self._pruneData(data_id_list)

    def _deleteRange(self, partition, min_tid=None, max_tid=None):
        sql = " WHERE partition=?"
        args = [partition]
        if min_tid:
            sql += " AND ? < tid"
            args.append(util.u64(min_tid))
        if max_tid:
            sql += " AND tid <= ?"
            args.append(util.u64(max_tid))
        q = self.query
        q("DELETE FROM trans" + sql, args)
        sql = " FROM obj" + sql
        data_id_list = [x for x, in q(
            "SELECT DISTINCT data_id%s AND data_id IS NOT NULL" % sql, args)]
        q("DELETE" + sql, args)
        self._pruneData(data_id_list)

    def getTransaction(self, tid, all=False):
        tid = util.u64(tid)
        q = self.query
        r = q("SELECT oids, user, description, ext, packed, ttid"
              " FROM trans WHERE partition=? AND tid=?",
              (self._getReadablePartition(tid), tid)).fetchone()
        if not r and all:
            r = q("SELECT oids, user, description, ext, packed, ttid"
                  " FROM ttrans WHERE tid=?", (tid,)).fetchone()
        if r:
            oids, user, description, ext, packed, ttid = r
            return splitOIDField(tid, oids), str(user), \
                str(description), str(ext), packed, util.p64(ttid)

    def getObjectHistory(self, oid, offset, length):
        # FIXME: This method doesn't take client's current transaction id as
        # parameter, which means it can return transactions in the future of
        # client's transaction.
        p64 = util.p64
        oid = util.u64(oid)
        return [(p64(tid), length or 0) for tid, length in self.query("""\
            SELECT tid, LENGTH(value)
                FROM obj LEFT JOIN data ON obj.data_id = data.id
                WHERE partition=? AND oid=? AND tid>=?
                ORDER BY tid DESC LIMIT ?,?""",
            (self._getReadablePartition(oid), oid,
             self._getPackTID(), offset, length))
            ] or None

    def _fetchObject(self, oid, tid):
        for serial, compression, checksum, data, value_serial in self.query(
                'SELECT tid, compression, data.hash, value, value_tid'
                ' FROM obj LEFT JOIN data ON obj.data_id = data.id'
                ' WHERE partition=? AND oid=? AND tid=?',
                (self._getReadablePartition(oid), oid, tid)):
            if checksum:
                checksum = str(checksum)
                data = str(data)
            return serial, compression, checksum, data, value_serial

    def getReplicationObjectList(self, min_tid, max_tid, length, partition,
            min_oid):
        u64 = util.u64
        p64 = util.p64
        min_tid = u64(min_tid)
        return [(p64(serial), p64(oid)) for serial, oid in self.query("""\
            SELECT tid, oid FROM obj
            WHERE partition=? AND tid<=?
            AND (tid=? AND ?<=oid OR ?<tid)
            ORDER BY tid ASC, oid ASC LIMIT ?""",
            (partition, u64(max_tid), min_tid, u64(min_oid), min_tid, length))]

    def _getTIDList(self, offset, length, partition_list):
        return (t[0] for t in self.query(
            "SELECT tid FROM trans WHERE `partition` in (%s)"
            " ORDER BY tid DESC LIMIT %d,%d"
            % (','.join(map(str, partition_list)), offset, length)))

    def getReplicationTIDList(self, min_tid, max_tid, length, partition):
        u64 = util.u64
        p64 = util.p64
        min_tid = u64(min_tid)
        max_tid = u64(max_tid)
        return [p64(t[0]) for t in self.query("""\
            SELECT tid FROM trans
            WHERE partition=? AND ?<=tid AND tid<=?
            ORDER BY tid ASC LIMIT ?""",
            (partition, min_tid, max_tid, length))]

    def _updatePackFuture(self, oid, orig_serial, max_serial):
        # Before deleting this objects revision, see if there is any
        # transaction referencing its value at max_serial or above.
        # If there is, copy value to the first future transaction. Any further
        # reference is just updated to point to the new data location.
        partition = self._getReadablePartition(oid)
        value_serial = None
        q = self.query
        for T in '', 't':
            update = """UPDATE OR FAIL %sobj SET value_tid=?
                         WHERE partition=? AND oid=? AND tid=?""" % T
            for serial, in q("""SELECT tid FROM %sobj
                    WHERE partition=? AND oid=? AND tid>=? AND value_tid=?
                    ORDER BY tid ASC""" % T,
                    (partition, oid, max_serial, orig_serial)):
                q(update, (value_serial, partition, oid, serial))
                if value_serial is None:
                    # First found, mark its serial for future reference.
                    value_serial = serial
        return value_serial

    def pack(self, tid, updateObjectDataForPack):
        # TODO: unit test (along with updatePackFuture)
        p64 = util.p64
        tid = util.u64(tid)
        updatePackFuture = self._updatePackFuture
        getPartition = self._getReadablePartition
        q = self.query
        self._setPackTID(tid)
        for count, oid, max_serial in q("SELECT COUNT(*) - 1, oid, MAX(tid)"
                                        " FROM obj WHERE tid<=? GROUP BY oid",
                                        (tid,)):
            partition = getPartition(oid)
            if q("SELECT 1 FROM obj WHERE partition=?"
                 " AND oid=? AND tid=? AND data_id IS NULL",
                 (partition, oid, max_serial)).fetchone():
                max_serial += 1
            elif not count:
                continue
            # There are things to delete for this object
            data_id_set = set()
            sql = " FROM obj WHERE partition=? AND oid=? AND tid<?"
            args = partition, oid, max_serial
            for serial, data_id in q("SELECT tid, data_id" + sql, args):
                data_id_set.add(data_id)
                new_serial = updatePackFuture(oid, serial, max_serial)
                if new_serial:
                    new_serial = p64(new_serial)
                updateObjectDataForPack(p64(oid), p64(serial),
                                        new_serial, data_id)
            q("DELETE" + sql, args)
            data_id_set.discard(None)
            self._pruneData(data_id_set)
        self.commit()

    def checkTIDRange(self, partition, length, min_tid, max_tid):
        # XXX: SQLite's GROUP_CONCAT is slow (looks like quadratic)
        count, tids, max_tid = self.query("""\
            SELECT COUNT(*), GROUP_CONCAT(tid), MAX(tid)
            FROM (SELECT tid FROM trans
                  WHERE partition=? AND ?<=tid AND tid<=?
                  ORDER BY tid ASC LIMIT ?) AS t""",
            (partition, util.u64(min_tid), util.u64(max_tid),
             -1 if length is None else length)).fetchone()
        if count:
            return count, sha1(tids).digest(), util.p64(max_tid)
        return 0, ZERO_HASH, ZERO_TID

    def checkSerialRange(self, partition, length, min_tid, max_tid, min_oid):
        u64 = util.u64
        # We don't ask SQLite to compute everything (like in checkTIDRange)
        # because it's difficult to get the last serial _for the last oid_.
        # We would need a function (that could be named 'LAST') that returns the
        # last grouped value, instead of the greatest one.
        min_tid = u64(min_tid)
        r = self.query("""\
            SELECT tid, oid
            FROM obj
            WHERE partition=? AND tid<=? AND (tid>? OR tid=? AND oid>=?)
            ORDER BY tid, oid LIMIT ?""",
            (partition, u64(max_tid), min_tid, min_tid, u64(min_oid),
             -1 if length is None else length)).fetchall()
        if r:
            p64 = util.p64
            return (len(r),
                    sha1(','.join(str(x[0]) for x in r)).digest(),
                    p64(r[-1][0]),
                    sha1(','.join(str(x[1]) for x in r)).digest(),
                    p64(r[-1][1]))
        return 0, ZERO_HASH, ZERO_TID, ZERO_HASH, ZERO_OID

    def dump(self):
        main = []
        data = []
        for line in self.conn.iterdump():
            if line.startswith('INSERT '):
                assert line.endswith(';'), line
                data.append(line)
                continue
            if line.startswith('CREATE TABLE '):
                # ALTER TABLE adds quotes.
                create, table, name, tail = line.split(' ', 3)
                line = ' '.join((create, table, name.strip('"'), tail))
            main.append(line)
        assert line == 'COMMIT;', line
        data.sort()
        main[-1:-1] = data
        return '\n'.join(main) + '\n'

    def restore(self, sql):
        self.conn.executescript(sql)