mysqldb.py 34.3 KB
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#
# Copyright (C) 2006-2017  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 binascii import a2b_hex
import MySQLdb
from MySQLdb import DataError, IntegrityError, \
    OperationalError, ProgrammingError
from MySQLdb.constants.CR import SERVER_GONE_ERROR, SERVER_LOST
from MySQLdb.constants.ER import DATA_TOO_LONG, DUP_ENTRY, NO_SUCH_TABLE
# BBB: the following 2 constants were added to mysqlclient 1.3.8
DROP_LAST_PARTITION = 1508
SAME_NAME_PARTITION = 1517
from array import array
from hashlib import sha1
import os
import re
import string
import struct
import sys
import time

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


def getPrintableQuery(query, max=70):
    return ''.join(c if c in string.printable and c not in '\t\x0b\x0c\r'
        else '\\x%02x' % ord(c) for c in query)


@implements
class MySQLDatabaseManager(DatabaseManager):
    """This class manages a database on MySQL."""

    VERSION = 1
    ENGINES = "InnoDB", "RocksDB", "TokuDB"
    _engine = ENGINES[0] # default engine

    _use_partition = False

    _max_allowed_packet = 32769 * 1024

    def _parse(self, database):
        """ Get the database credentials (username, password, database) """
        # expected pattern : [user[:password]@]database[(~|.|/)unix_socket]
        self.user, self.passwd, self.db, self.socket = re.match(
            '(?:([^:]+)(?::(.*))?@)?([^~./]+)(.+)?$', database).groups()

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

    def _connect(self):
        kwd = {'db' : self.db, 'user' : self.user}
        if self.passwd is not None:
            kwd['passwd'] = self.passwd
        if self.socket:
            kwd['unix_socket'] = os.path.expanduser(self.socket)
        logging.info('connecting to MySQL on the database %s with user %s',
                     self.db, self.user)
        if self._wait < 0:
            timeout_at = None
        else:
            timeout_at = time.time() + self._wait
        last = None
        while True:
            try:
                self.conn = MySQLdb.connect(**kwd)
                break
            except Exception as e:
                if None is not timeout_at <= time.time():
                    raise
                e = str(e)
                if last == e:
                    log = logging.debug
                else:
                    last = e
                    log = logging.exception
                log('Connection to MySQL failed, retrying.')
                time.sleep(1)
        self._active = 0
        self._config = {}
        conn = self.conn
        conn.autocommit(False)
        conn.query("SET SESSION group_concat_max_len = %u" % (2**32-1))
        conn.set_sql_mode("TRADITIONAL,NO_ENGINE_SUBSTITUTION")
        def query(sql):
            conn.query(sql)
            r = conn.store_result()
            return r.fetch_row(r.num_rows())
        if self.LOCK:
            (locked,), = query("SELECT GET_LOCK('%s.%s', 0)"
                % (self.db, self.LOCK))
            if not locked:
                sys.exit(self.LOCKED)
        (name, value), = query(
            "SHOW VARIABLES WHERE variable_name='max_allowed_packet'")
        if int(value) < self._max_allowed_packet:
            raise DatabaseFailure("Global variable %r is too small."
                " Minimal value must be %uk."
                % (name, self._max_allowed_packet // 1024))
        self._max_allowed_packet = int(value)

    def _commit(self):
        self.conn.commit()
        self._active = 0

    def query(self, query):
        """Query data from a database."""
        if LOG_QUERIES:
            logging.debug('querying %s...',
                getPrintableQuery(query.split('\n', 1)[0][:70]))
        # Try 3 times at most. When it fails too often for the same
        # query then the disconnection is likely caused by this query.
        # We don't want to enter into an infinite loop.
        retry = 2
        while 1:
            conn = self.conn
            try:
                conn.query(query)
                if query.startswith("SELECT "):
                    r = conn.store_result()
                    return tuple([
                        tuple([d.tostring() if isinstance(d, array) else d
                              for d in row])
                        for row in r.fetch_row(r.num_rows())])
                break
            except OperationalError as m:
                code, m = m.args
                # IDEA: Is it safe to retry in case of DISK_FULL ?
                # XXX:  However, this would another case of failure that would
                #       be unnoticed by other nodes (ADMIN & MASTER). When
                #       there are replicas, it may be preferred to not retry.
                if self._active or SERVER_GONE_ERROR != code != SERVER_LOST \
                   or not retry:
                    raise DatabaseFailure('MySQL error %d: %s\nQuery: %s'
                        % (code, m, getPrintableQuery(query[:1000])))
                logging.info('the MySQL server is gone; reconnecting')
                self._connect()
                retry -= 1
        r = query.split(None, 1)[0]
        if r in ("INSERT", "REPLACE", "DELETE", "UPDATE"):
            self._active = 1
        else:
            assert r in ("ALTER", "CREATE", "DROP"), query

    @property
    def escape(self):
        """Escape special characters in a string."""
        return self.conn.escape_string

    def erase(self):
        self.query("DROP TABLE IF EXISTS"
            " config, pt, trans, obj, data, bigdata, ttrans, tobj")

    def nonempty(self, table):
        try:
            return bool(self.query("SELECT 1 FROM %s LIMIT 1" % table))
        except ProgrammingError as e:
            if e.args[0] != NO_SUCH_TABLE:
                raise

    def _setup(self, dedup=False):
        self._config.clear()
        q = self.query
        p = engine = self._engine

        if self.nonempty("config") is None:
            # The table "config" stores configuration
            # parameters which affect the persistent data.
            q("""CREATE TABLE config (
                     name VARBINARY(255) NOT NULL PRIMARY KEY,
                     value VARBINARY(255) NULL
                 ) ENGINE=""" + engine)
        else:
            # Automatic migration.
            version = self._getVersion()
            if version < 1:
                self._checkNoUnfinishedTransactions()
                q("DROP TABLE IF EXISTS ttrans")

        self._setConfiguration("version", self.VERSION)

        # The table "pt" stores a partition table.
        q("""CREATE TABLE IF NOT EXISTS pt (
                 rid INT UNSIGNED NOT NULL,
                 nid INT NOT NULL,
                 state TINYINT UNSIGNED NOT NULL,
                 PRIMARY KEY (rid, nid)
             ) ENGINE=""" + engine)

        if self._use_partition:
            p += """ PARTITION BY LIST (`partition`) (
                PARTITION dummy VALUES IN (NULL))"""

        # The table "trans" stores information on committed transactions.
        q("""CREATE TABLE IF NOT EXISTS trans (
                 `partition` SMALLINT UNSIGNED NOT NULL,
                 tid BIGINT UNSIGNED NOT NULL,
                 packed BOOLEAN NOT NULL,
                 oids MEDIUMBLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid BIGINT UNSIGNED NOT NULL,
                 PRIMARY KEY (`partition`, tid)
             ) ENGINE=""" + p)

        # The table "obj" stores committed object metadata.
        q("""CREATE TABLE IF NOT EXISTS obj (
                 `partition` SMALLINT UNSIGNED NOT NULL,
                 oid BIGINT UNSIGNED NOT NULL,
                 tid BIGINT UNSIGNED NOT NULL,
                 data_id BIGINT UNSIGNED NULL,
                 value_tid BIGINT UNSIGNED NULL,
                 PRIMARY KEY (`partition`, tid, oid),
                 KEY (`partition`, oid, tid),
                 KEY (data_id)
             ) ENGINE=""" + p)

        if engine == "TokuDB":
            engine += " compression='tokudb_uncompressed'"

        # The table "data" stores object data.
        # We'd like to have partial index on 'hash' column (e.g. hash(4))
        # but 'UNIQUE' constraint would not work as expected.
        q("""CREATE TABLE IF NOT EXISTS data (
                 id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
                 hash BINARY(20) NOT NULL,
                 compression TINYINT UNSIGNED NULL,
                 value MEDIUMBLOB NOT NULL%s
             ) ENGINE=%s""" % (""",
                 UNIQUE (hash, compression)""" if dedup else "", engine))

        q("""CREATE TABLE IF NOT EXISTS bigdata (
                 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
                 value MEDIUMBLOB NOT NULL
             ) ENGINE=""" + engine)

        # The table "ttrans" stores information on uncommitted transactions.
        q("""CREATE TABLE IF NOT EXISTS ttrans (
                 `partition` SMALLINT UNSIGNED NOT NULL,
                 tid BIGINT UNSIGNED,
                 packed BOOLEAN NOT NULL,
                 oids MEDIUMBLOB NOT NULL,
                 user BLOB NOT NULL,
                 description BLOB NOT NULL,
                 ext BLOB NOT NULL,
                 ttid BIGINT UNSIGNED NOT NULL
             ) ENGINE=""" + engine)

        # The table "tobj" stores uncommitted object metadata.
        q("""CREATE TABLE IF NOT EXISTS tobj (
                 `partition` SMALLINT UNSIGNED NOT NULL,
                 oid BIGINT UNSIGNED NOT NULL,
                 tid BIGINT UNSIGNED NOT NULL,
                 data_id BIGINT UNSIGNED NULL,
                 value_tid BIGINT UNSIGNED NULL,
                 PRIMARY KEY (tid, oid)
             ) ENGINE=""" + engine)

        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:
            sql_key = self.escape(str(key))
            try:
                r = self.query("SELECT value FROM config WHERE name = '%s'"
                               % sql_key)[0][0]
            except IndexError:
                r = None
            self._config[key] = r
            return r

    def _setConfiguration(self, key, value):
        q = self.query
        e = self.escape
        self._config[key] = value
        k = e(str(key))
        if value is None:
            q("DELETE FROM config WHERE name = '%s'" % k)
            return
        value = str(value)
        sql = "REPLACE INTO config VALUES ('%s', '%s')" % (k, e(value))
        try:
            q(sql)
        except DataError as e:
            if e.args[0] != DATA_TOO_LONG or len(value) < 256 or key != "zodb":
                raise
            q("ALTER TABLE config MODIFY value VARBINARY(%s) NULL" % len(value))
            q(sql)

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

    def _getAssignedPartitionList(self):
        nid = self.getUUID()
        if nid is None:
            return ()
        return [p for p, in self.query("SELECT rid FROM pt WHERE nid=%s" % nid)]

    def _sqlmax(self, sql, arg_list):
        q = self.query
        x = [x for x in arg_list for x, in q(sql % x) if x is not None]
        if x: return max(x)

    def getLastTID(self, max_tid):
        return self._sqlmax(
            "SELECT MAX(tid) as t FROM trans FORCE INDEX (PRIMARY)"
            " WHERE tid<=%s and `partition`=%%s" % max_tid,
            self._getAssignedPartitionList())

    def _getLastIDs(self):
        offset_list = self._getAssignedPartitionList()
        p64 = util.p64
        q = self.query
        sql = ("SELECT MAX(tid) FROM %s FORCE INDEX (PRIMARY)"
               " WHERE `partition`=%s")
        trans, obj = ({partition: p64(tid)
            for partition in offset_list
            for tid, in q(sql % (t, partition))
            if tid is not None}
            for t in ('trans', 'obj'))
        oid = self._sqlmax(
            "SELECT MAX(oid) FROM obj FORCE INDEX (`partition`)"
            " WHERE `partition`=%s", offset_list)
        return trans, obj, None if oid is None else p64(oid)

    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)
        # MariaDB is smart enough to realize that 'ttid' is constant.
        r = self.query("SELECT tid FROM trans"
            " WHERE `partition`=%s AND tid>=ttid AND ttid=%s LIMIT 1"
            % (self._getReadablePartition(ttid), ttid))
        if r:
            return util.p64(r[0][0])

    def getLastObjectTID(self, oid):
        oid = util.u64(oid)
        r = self.query("SELECT tid FROM obj FORCE INDEX(`partition`)"
                       " WHERE `partition`=%d AND oid=%d"
                       " ORDER BY tid DESC LIMIT 1"
                       % (self._getReadablePartition(oid), oid))
        return util.p64(r[0][0]) if r else None

    def _getNextTID(self, *args): # partition, oid, tid
        r = self.query("SELECT tid FROM obj"
                       " FORCE INDEX(`partition`)"
                       " WHERE `partition`=%d AND oid=%d AND tid>%d"
                       " ORDER BY tid LIMIT 1" % args)
        return r[0][0] if r else None

    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 FORCE INDEX(`partition`)'
               ' LEFT JOIN data ON (obj.data_id = data.id)'
               ' WHERE `partition` = %d AND oid = %d') % (partition, oid)
        if before_tid is not None:
            sql += ' AND tid < %d ORDER BY tid DESC LIMIT 1' % before_tid
        elif tid is not None:
            sql += ' AND tid = %d' % tid
        else:
            # XXX I want to express "HAVING tid = MAX(tid)", but
            # MySQL does not use an index for a HAVING clause!
            sql += ' ORDER BY tid DESC LIMIT 1'
        r = q(sql)
        try:
            serial, compression, checksum, data, value_serial = r[0]
        except IndexError:
            return None
        if compression and compression & 0x80:
            compression &= 0x7f
            data = ''.join(self._bigData(data))
        return (serial, self._getNextTID(partition, oid, serial),
                compression, checksum, data, value_serial)

    def _changePartitionTable(self, cell_list, reset=False):
        offset_list = []
        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
            if state == CellStates.DISCARDED:
                q("DELETE FROM pt WHERE rid = %d AND nid = %d"
                  % (offset, nid))
            else:
                offset_list.append(offset)
                q("INSERT INTO pt VALUES (%d, %d, %d)"
                  " ON DUPLICATE KEY UPDATE state = %d"
                  % (offset, nid, state, state))
        if self._use_partition:
            for offset in offset_list:
                add = """ALTER TABLE %%s ADD PARTITION (
                    PARTITION p%u VALUES IN (%u))""" % (offset, offset)
                for table in 'trans', 'obj':
                    try:
                        self.conn.query(add % table)
                    except OperationalError as e:
                        if e.args[0] != SAME_NAME_PARTITION:
                            raise

    def dropPartitions(self, offset_list):
        q = self.query
        # XXX: these queries are inefficient (execution time increase with
        # row count, although we use indexes) when there are rows to
        # delete. It should be done as an idle task, by chunks.
        for partition in offset_list:
            where = " WHERE `partition`=%d" % partition
            data_id_list = [x for x, in
                q("SELECT DISTINCT data_id FROM obj FORCE INDEX(PRIMARY)"
                  + where)
                if x]
            if not self._use_partition:
                q("DELETE FROM obj" + where)
                q("DELETE FROM trans" + where)
            self._pruneData(data_id_list)
        if self._use_partition:
            drop = "ALTER TABLE %s DROP PARTITION" + \
                ','.join(' p%u' % i for i in offset_list)
            for table in 'trans', 'obj':
                try:
                    self.conn.query(drop % table)
                except OperationalError as e:
                    if e.args[0] != DROP_LAST_PARTITION:
                        raise

    def _getUnfinishedDataIdList(self):
        return [x for x, in self.query("SELECT data_id FROM tobj") if x]

    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):
        e = self.escape
        u64 = util.u64
        tid = u64(tid)
        if temporary:
            obj_table = 'tobj'
            trans_table = 'ttrans'
        else:
            obj_table = 'obj'
            trans_table = 'trans'
        q = self.query
        sql = ["REPLACE INTO %s VALUES " % obj_table]
        values_max = self._max_allowed_packet - len(sql[0])
        values_size = 0
        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`=%d AND oid=%d AND tid=%d"
                    % (partition, oid, value_serial))
                if temporary:
                    self.holdData(data_id)
            else:
                value_serial = 'NULL'
            value = "(%s,%s,%s,%s,%s)," % (
                partition, oid, tid, data_id or 'NULL', value_serial)
            values_size += len(value)
            # actually: max_values < values_size + EXTRA - len(final comma)
            # (test_max_allowed_packet checks that EXTRA == 2)
            if values_max <= values_size:
                sql[-1] = sql[-1][:-1] # remove final comma
                q(''.join(sql))
                del sql[1:]
                values_size = len(value)
            sql.append(value)
        if values_size:
            sql[-1] = value[:-1] # remove final comma
            q(''.join(sql))
        if transaction:
            oid_list, user, desc, ext, packed, ttid = transaction
            partition = self._getPartition(tid)
            assert packed in (0, 1)
            q("REPLACE INTO %s VALUES (%s,%s,%s,'%s','%s','%s','%s',%s)" % (
                trans_table, partition, 'NULL' if temporary else tid, packed,
                e(''.join(oid_list)), e(user), e(desc), e(ext), u64(ttid)))

    _structLL = struct.Struct(">LL")
    _unpackLL = _structLL.unpack

    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
            id_list = []
            bigid_list = []
            for id, value in q("SELECT id, IF(compression < 128, NULL, value)"
                               " FROM data LEFT JOIN obj ON (id = data_id)"
                               " WHERE id IN (%s) AND data_id IS NULL"
                               % ",".join(map(str, data_id_list))):
                id_list.append(str(id))
                if value:
                    bigdata_id, length = self._unpackLL(value)
                    bigid_list += xrange(bigdata_id,
                                         bigdata_id + (length + 0x7fffff >> 23))
            if id_list:
                q("DELETE FROM data WHERE id IN (%s)" % ",".join(id_list))
                if bigid_list:
                    q("DELETE FROM bigdata WHERE id IN (%s)"
                      % ",".join(map(str, bigid_list)))
                return len(id_list)
        return 0

    def _bigData(self, value):
        bigdata_id, length = self._unpackLL(value)
        q = self.query
        return (q("SELECT value FROM bigdata WHERE id=%s" % i)[0][0]
            for i in xrange(bigdata_id,
                            bigdata_id + (length + 0x7fffff >> 23)))

    def storeData(self, checksum, data, compression, _pack=_structLL.pack):
        e = self.escape
        checksum = e(checksum)
        if 0x1000000 <= len(data): # 16M (MEDIUMBLOB limit)
            compression |= 0x80
            q = self.query
            for r, d in q("SELECT id, value FROM data"
                          " WHERE hash='%s' AND compression=%s"
                          % (checksum, compression)):
                i = 0
                for d in self._bigData(d):
                    j = i + len(d)
                    if data[i:j] != d:
                        raise IntegrityError(DUP_ENTRY)
                    i = j
                if j != len(data):
                    raise IntegrityError(DUP_ENTRY)
                return r
            i = 'NULL'
            length = len(data)
            for j in xrange(0, length, 0x800000): # 8M
                q("INSERT INTO bigdata VALUES (%s, '%s')"
                  % (i, e(data[j:j+0x800000])))
                if not j:
                    i = bigdata_id = self.conn.insert_id()
                i += 1
            data = _pack(bigdata_id, length)
        try:
            self.query("INSERT INTO data VALUES (NULL, '%s', %d, '%s')" %
                       (checksum, compression,  e(data)))
        except IntegrityError as e:
            if e.args[0] == DUP_ENTRY:
                (r, d), = self.query("SELECT id, value FROM data"
                                     " WHERE hash='%s' AND compression=%s"
                                     % (checksum, compression))
                if d == data:
                    return r
            raise
        return self.conn.insert_id()

    def loadData(self, data_id):
        compression, hash, value = self.query(
            "SELECT compression, hash, value FROM data where id=%s"
            % data_id)[0]
        if compression and compression & 0x80:
            compression &= 0x7f
            data = ''.join(self._bigData(data))
        return compression, hash, value

    del _structLL

    def _getDataTID(self, oid, tid=None, before_tid=None):
        sql = ('SELECT tid, value_tid FROM obj FORCE INDEX(`partition`)'
               ' WHERE `partition` = %d AND oid = %d'
              ) % (self._getReadablePartition(oid), oid)
        if tid is not None:
            sql += ' AND tid = %d' % tid
        elif before_tid is not None:
            sql += ' AND tid < %d ORDER BY tid DESC LIMIT 1' % before_tid
        else:
            # XXX I want to express "HAVING tid = MAX(tid)", but
            # MySQL does not use an index for a HAVING clause!
            sql += ' ORDER BY tid DESC LIMIT 1'
        r = self.query(sql)
        return r[0] if r else (None, None)

    def lockTransaction(self, tid, ttid):
        u64 = util.u64
        self.query("UPDATE ttrans SET tid=%d WHERE ttid=%d LIMIT 1"
                   % (u64(tid), u64(ttid)))
        self.commit()

    def unlockTransaction(self, tid, ttid):
        q = self.query
        u64 = util.u64
        tid = u64(tid)
        sql = " FROM tobj WHERE tid=%d" % u64(ttid)
        data_id_list = [x for x, in q("SELECT data_id" + sql) if x]
        q("INSERT INTO obj SELECT `partition`, oid, %d, data_id, value_tid %s"
          % (tid, sql))
        q("DELETE" + sql)
        q("INSERT INTO trans SELECT * FROM ttrans WHERE tid=%d" % tid)
        q("DELETE FROM ttrans WHERE tid=%d" % tid)
        self.releaseData(data_id_list)

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

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

    def deleteObject(self, oid, serial=None):
        u64 = util.u64
        oid = u64(oid)
        sql = " FROM obj WHERE `partition`=%d AND oid=%d" \
            % (self._getPartition(oid), oid)
        if serial:
            sql += ' AND tid=%d' % u64(serial)
        q = self.query
        data_id_list = [x for x, in q("SELECT DISTINCT data_id" + sql) if x]
        q("DELETE" + sql)
        self._pruneData(data_id_list)

    def _deleteRange(self, partition, min_tid=None, max_tid=None):
        sql = " WHERE `partition`=%d" % partition
        if min_tid:
            sql += " AND %d < tid" % util.u64(min_tid)
        if max_tid:
            sql += " AND tid <= %d" % util.u64(max_tid)
        q = self.query
        q("DELETE FROM trans" + sql)
        sql = " FROM obj" + sql
        data_id_list = [x for x, in q("SELECT DISTINCT data_id" + sql) if x]
        q("DELETE" + sql)
        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` = %d AND tid = %d"
              % (self._getReadablePartition(tid), tid))
        if not r and all:
            r = q("SELECT oids, user, description, ext, packed, ttid"
                  " FROM ttrans WHERE tid = %d" % tid)
        if r:
            oids, user, desc, ext, packed, ttid = r[0]
            oid_list = splitOIDField(tid, oids)
            return oid_list, user, desc, ext, bool(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.
        oid = util.u64(oid)
        p64 = util.p64
        r = self.query("SELECT tid, IF(compression < 128, LENGTH(value),"
            "  CAST(CONV(HEX(SUBSTR(value, 5, 4)), 16, 10) AS INT))"
            " FROM obj FORCE INDEX(`partition`)"
            " LEFT JOIN data ON (obj.data_id = data.id)"
            " WHERE `partition` = %d AND oid = %d AND tid >= %d"
            " ORDER BY tid DESC LIMIT %d, %d" %
            (self._getReadablePartition(oid), oid,
             self._getPackTID(), offset, length))
        if r:
            return [(p64(tid), length or 0) for tid, length in r]

    def _fetchObject(self, oid, tid):
        r = self.query(
            'SELECT tid, compression, data.hash, value, value_tid'
            ' FROM obj FORCE INDEX(`partition`)'
            ' LEFT JOIN data ON (obj.data_id = data.id)'
            ' WHERE `partition` = %d AND oid = %d AND tid = %d'
            % (self._getReadablePartition(oid), oid, tid))
        if r:
            r = r[0]
            compression = r[1]
            if compression and compression & 0x80:
                return (r[0], compression & 0x7f, r[2],
                    ''.join(self._bigData(data)), r[4])
            return r

    def getReplicationObjectList(self, min_tid, max_tid, length, partition,
            min_oid):
        u64 = util.u64
        p64 = util.p64
        min_tid = u64(min_tid)
        r = self.query('SELECT tid, oid FROM obj FORCE INDEX(PRIMARY)'
                       ' WHERE `partition` = %d AND tid <= %d'
                       ' AND (tid = %d AND %d <= oid OR %d < tid)'
                       ' ORDER BY tid ASC, oid ASC LIMIT %d' % (
            partition, u64(max_tid), min_tid, u64(min_oid), min_tid, length))
        return [(p64(serial), p64(oid)) for serial, oid in r]

    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)
        r = self.query("""SELECT tid FROM trans
                    WHERE `partition` = %(partition)d
                    AND tid >= %(min_tid)d AND tid <= %(max_tid)d
                    ORDER BY tid ASC LIMIT %(length)d""" % {
            'partition': partition,
            'min_tid': min_tid,
            'max_tid': max_tid,
            'length': length,
        })
        return [p64(t[0]) for t in r]

    def _updatePackFuture(self, oid, orig_serial, max_serial):
        q = self.query
        # 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.
        value_serial = None
        kw = {
          'partition': self._getReadablePartition(oid),
          'oid': oid,
          'orig_tid': orig_serial,
          'max_tid': max_serial,
          'new_tid': 'NULL',
        }
        for kw['table'] in 'obj', 'tobj':
            for kw['tid'], in q('SELECT tid FROM %(table)s'
                  ' WHERE `partition`=%(partition)d AND oid=%(oid)d'
                  ' AND tid>=%(max_tid)d AND value_tid=%(orig_tid)d'
                  ' ORDER BY tid ASC' % kw):
                q('UPDATE %(table)s SET value_tid=%(new_tid)s'
                  ' WHERE `partition`=%(partition)d AND oid=%(oid)d'
                  ' AND tid=%(tid)d' % kw)
                if value_serial is None:
                    # First found, mark its serial for future reference.
                    kw['new_tid'] = value_serial = kw['tid']
        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 FORCE INDEX(`partition`)"
                                        " WHERE tid <= %d GROUP BY oid"
                                        % tid):
            partition = getPartition(oid)
            if q("SELECT 1 FROM obj WHERE `partition` = %d"
                 " AND oid = %d AND tid = %d AND data_id IS NULL"
                 % (partition, oid, max_serial)):
                max_serial += 1
            elif not count:
                continue
            # There are things to delete for this object
            data_id_set = set()
            sql = ' FROM obj WHERE `partition`=%d AND oid=%d' \
                ' AND tid<%d' % (partition, oid, max_serial)
            for serial, data_id in q('SELECT tid, data_id' + sql):
                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)
            data_id_set.discard(None)
            self._pruneData(data_id_set)
        self.commit()

    def checkTIDRange(self, partition, length, min_tid, max_tid):
        count, tid_checksum, max_tid = self.query(
            """SELECT COUNT(*), SHA1(GROUP_CONCAT(tid SEPARATOR ",")), MAX(tid)
               FROM (SELECT tid FROM trans
                     WHERE `partition` = %(partition)s
                       AND tid >= %(min_tid)d
                       AND tid <= %(max_tid)d
                     ORDER BY tid ASC %(limit)s) AS t""" % {
            'partition': partition,
            'min_tid': util.u64(min_tid),
            'max_tid': util.u64(max_tid),
            'limit': '' if length is None else 'LIMIT %u' % length,
        })[0]
        if count:
            return count, a2b_hex(tid_checksum), 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 MySQL 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.
        r = self.query(
            """SELECT tid, oid
               FROM obj FORCE INDEX(PRIMARY)
               WHERE `partition` = %(partition)s
                 AND tid <= %(max_tid)d
                 AND (tid > %(min_tid)d OR
                      tid = %(min_tid)d AND oid >= %(min_oid)d)
               ORDER BY tid, oid %(limit)s""" % {
            'min_oid': u64(min_oid),
            'min_tid': u64(min_tid),
            'max_tid': u64(max_tid),
            'limit': '' if length is None else 'LIMIT %u' % length,
            'partition': partition,
        })
        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