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1903 lines (1458 loc) · 59.4 KB
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"""Core disk and file backed cache API.
"""
import codecs
import contextlib as cl
import errno
import functools as ft
import io
import os
import os.path as op
import pickletools
import sqlite3
import struct
import sys
import threading
import time
import warnings
import zlib
if sys.hexversion < 0x03000000:
import cPickle as pickle # pylint: disable=import-error
# ISSUE #25 Fix for http://bugs.python.org/issue10211
from cStringIO import StringIO as BytesIO # pylint: disable=import-error
TextType = unicode # pylint: disable=invalid-name,undefined-variable
BytesType = str
INT_TYPES = int, long # pylint: disable=undefined-variable
range = xrange # pylint: disable=redefined-builtin,invalid-name,undefined-variable
io_open = io.open # pylint: disable=invalid-name
else:
import pickle
from io import BytesIO # pylint: disable=ungrouped-imports
TextType = str
BytesType = bytes
INT_TYPES = (int,)
io_open = open # pylint: disable=invalid-name
try:
WindowsError
except NameError:
class WindowsError(Exception):
"Windows error place-holder on platforms without support."
pass
class Constant(tuple):
"Pretty display of immutable constant."
def __new__(cls, name):
return tuple.__new__(cls, (name,))
def __repr__(self):
return '%s' % self[0]
DBNAME = 'cache.db'
ENOVAL = Constant('ENOVAL')
UNKNOWN = Constant('UNKNOWN')
MODE_NONE = 0
MODE_RAW = 1
MODE_BINARY = 2
MODE_TEXT = 3
MODE_PICKLE = 4
DEFAULT_SETTINGS = {
u'statistics': 0, # False
u'tag_index': 0, # False
u'eviction_policy': u'least-recently-stored',
u'size_limit': 2 ** 30, # 1gb
u'cull_limit': 10,
u'sqlite_auto_vacuum': 1, # FULL
u'sqlite_cache_size': 2 ** 13, # 8,192 pages
u'sqlite_journal_mode': u'wal',
u'sqlite_mmap_size': 2 ** 26, # 64mb
u'sqlite_synchronous': 1, # NORMAL
u'disk_min_file_size': 2 ** 15, # 32kb
u'disk_pickle_protocol': pickle.HIGHEST_PROTOCOL,
}
METADATA = {
u'count': 0,
u'size': 0,
u'hits': 0,
u'misses': 0,
}
EVICTION_POLICY = {
'none': {
'init': None,
'get': None,
'cull': None,
},
'least-recently-stored': {
'init': (
'CREATE INDEX IF NOT EXISTS Cache_store_time ON'
' Cache (store_time)'
),
'get': None,
'cull': 'SELECT {fields} FROM Cache ORDER BY store_time LIMIT ?',
},
'least-recently-used': {
'init': (
'CREATE INDEX IF NOT EXISTS Cache_access_time ON'
' Cache (access_time)'
),
'get': 'access_time = {now}',
'cull': 'SELECT {fields} FROM Cache ORDER BY access_time LIMIT ?',
},
'least-frequently-used': {
'init': (
'CREATE INDEX IF NOT EXISTS Cache_access_count ON'
' Cache (access_count)'
),
'get': 'access_count = access_count + 1',
'cull': 'SELECT {fields} FROM Cache ORDER BY access_count LIMIT ?',
},
}
class Disk(object):
"Cache key and value serialization for SQLite database and files."
def __init__(self, directory, min_file_size=0, pickle_protocol=0):
"""Initialize disk instance.
:param str directory: directory path
:param int min_file_size: minimum size for file use
:param int pickle_protocol: pickle protocol for serialization
"""
self._directory = directory
self.min_file_size = min_file_size
self.pickle_protocol = pickle_protocol
def hash(self, key):
"""Compute portable hash for `key`.
:param key: key to hash
:return: hash value
"""
mask = 0xFFFFFFFF
disk_key, _ = self.put(key)
type_disk_key = type(disk_key)
if type_disk_key is sqlite3.Binary:
return zlib.adler32(disk_key) & mask
elif type_disk_key is TextType:
return zlib.adler32(disk_key.encode('utf-8')) & mask # pylint: disable=no-member
elif type_disk_key in INT_TYPES:
return disk_key % mask
else:
assert type_disk_key is float
return zlib.adler32(struct.pack('!d', disk_key)) & mask
def put(self, key):
"""Convert `key` to fields key and raw for Cache table.
:param key: key to convert
:return: (database key, raw boolean) pair
"""
# pylint: disable=bad-continuation,unidiomatic-typecheck
type_key = type(key)
if type_key is BytesType:
return sqlite3.Binary(key), True
elif ((type_key is TextType)
or (type_key in INT_TYPES
and -9223372036854775808 <= key <= 9223372036854775807)
or (type_key is float)):
return key, True
else:
data = pickle.dumps(key, protocol=self.pickle_protocol)
result = pickletools.optimize(data)
return sqlite3.Binary(result), False
def get(self, key, raw):
"""Convert fields `key` and `raw` from Cache table to key.
:param key: database key to convert
:param bool raw: flag indicating raw database storage
:return: corresponding Python key
"""
# pylint: disable=no-self-use,unidiomatic-typecheck
if raw:
return BytesType(key) if type(key) is sqlite3.Binary else key
else:
return pickle.load(BytesIO(key))
def store(self, value, read, key=UNKNOWN):
"""Convert `value` to fields size, mode, filename, and value for Cache
table.
:param value: value to convert
:param bool read: True when value is file-like object
:param key: key for item (default UNKNOWN)
:return: (size, mode, filename, value) tuple for Cache table
"""
# pylint: disable=unidiomatic-typecheck
type_value = type(value)
min_file_size = self.min_file_size
if ((type_value is TextType and len(value) < min_file_size)
or (type_value in INT_TYPES
and -9223372036854775808 <= value <= 9223372036854775807)
or (type_value is float)):
return 0, MODE_RAW, None, value
elif type_value is BytesType:
if len(value) < min_file_size:
return 0, MODE_RAW, None, sqlite3.Binary(value)
else:
filename, full_path = self.filename(key, value)
with open(full_path, 'wb') as writer:
writer.write(value)
return len(value), MODE_BINARY, filename, None
elif type_value is TextType:
filename, full_path = self.filename(key, value)
with io_open(full_path, 'w', encoding='UTF-8') as writer:
writer.write(value)
size = op.getsize(full_path)
return size, MODE_TEXT, filename, None
elif read:
size = 0
reader = ft.partial(value.read, 2 ** 22)
filename, full_path = self.filename(key, value)
with open(full_path, 'wb') as writer:
for chunk in iter(reader, b''):
size += len(chunk)
writer.write(chunk)
return size, MODE_BINARY, filename, None
else:
result = pickle.dumps(value, protocol=self.pickle_protocol)
if len(result) < min_file_size:
return 0, MODE_PICKLE, None, sqlite3.Binary(result)
else:
filename, full_path = self.filename(key, value)
with open(full_path, 'wb') as writer:
writer.write(result)
return len(result), MODE_PICKLE, filename, None
def fetch(self, mode, filename, value, read):
"""Convert fields `mode`, `filename`, and `value` from Cache table to
value.
:param int mode: value mode raw, binary, text, or pickle
:param str filename: filename of corresponding value
:param value: database value
:param bool read: when True, return an open file handle
:return: corresponding Python value
"""
# pylint: disable=no-self-use,unidiomatic-typecheck
if mode == MODE_RAW:
return BytesType(value) if type(value) is sqlite3.Binary else value
elif mode == MODE_BINARY:
if read:
return open(op.join(self._directory, filename), 'rb')
else:
with open(op.join(self._directory, filename), 'rb') as reader:
return reader.read()
elif mode == MODE_TEXT:
full_path = op.join(self._directory, filename)
with io_open(full_path, 'r', encoding='UTF-8') as reader:
return reader.read()
elif mode == MODE_PICKLE:
if value is None:
with open(op.join(self._directory, filename), 'rb') as reader:
return pickle.load(reader)
else:
return pickle.load(BytesIO(value))
def filename(self, key=UNKNOWN, value=UNKNOWN):
"""Return filename and full-path tuple for file storage.
Filename will be a randomly generated 28 character hexadecimal string
with ".val" suffixed. Two levels of sub-directories will be used to
reduce the size of directories. On older filesystems, lookups in
directories with many files may be slow.
The default implementation ignores the `key` and `value` parameters.
In some scenarios, for example :meth:`Cache.push
<diskcache.Cache.push>`, the `key` or `value` may not be known when the
item is stored in the cache.
:param key: key for item (default UNKNOWN)
:param value: value for item (default UNKNOWN)
"""
# pylint: disable=unused-argument
hex_name = codecs.encode(os.urandom(16), 'hex').decode('utf-8')
sub_dir = op.join(hex_name[:2], hex_name[2:4])
name = hex_name[4:] + '.val'
directory = op.join(self._directory, sub_dir)
try:
os.makedirs(directory)
except OSError as error:
if error.errno != errno.EEXIST:
raise
filename = op.join(sub_dir, name)
full_path = op.join(self._directory, filename)
return filename, full_path
def remove(self, filename):
"""Remove a file given by `filename`.
This method is cross-thread and cross-process safe. If an "error no
entry" occurs, it is suppressed.
:param str filename: relative path to file
"""
full_path = op.join(self._directory, filename)
try:
os.remove(full_path)
except WindowsError:
pass
except OSError as error:
if error.errno != errno.ENOENT:
# ENOENT may occur if two caches attempt to delete the same
# file at the same time.
raise
class Timeout(Exception):
"Database timeout expired."
pass
class UnknownFileWarning(UserWarning):
"Warning used by Cache.check for unknown files."
pass
class EmptyDirWarning(UserWarning):
"Warning used by Cache.check for empty directories."
pass
class Cache(object):
"Disk and file backed cache."
# pylint: disable=bad-continuation
def __init__(self, directory, timeout=60, disk=Disk, **settings):
"""Initialize cache instance.
:param str directory: cache directory
:param float timeout: SQLite connection timeout
:param disk: Disk type or subclass for serialization
:param settings: any of DEFAULT_SETTINGS
"""
try:
assert issubclass(disk, Disk)
except (TypeError, AssertionError):
raise ValueError('disk must subclass diskcache.Disk')
self._directory = directory
self._timeout = 60 # Use 1 minute timeout for initialization.
self._local = threading.local()
if not op.isdir(directory):
try:
os.makedirs(directory, 0o755)
except OSError as error:
if error.errno != errno.EEXIST:
raise EnvironmentError(
error.errno,
'Cache directory "%s" does not exist'
' and could not be created' % self._directory
)
sql = self._sql
# Setup Settings table.
try:
current_settings = dict(sql(
'SELECT key, value FROM Settings'
).fetchall())
except sqlite3.OperationalError:
current_settings = {}
sets = DEFAULT_SETTINGS.copy()
sets.update(current_settings)
sets.update(settings)
for key in METADATA:
sets.pop(key, None)
# Chance to set pragmas before any tables are created.
for key, value in sorted(sets.items()):
if not key.startswith('sqlite_'):
continue
self.reset(key, value, update=False)
sql('CREATE TABLE IF NOT EXISTS Settings ('
' key TEXT NOT NULL UNIQUE,'
' value)'
)
# Setup Disk object (must happen after settings initialized).
kwargs = {
key[5:]: value for key, value in sets.items()
if key.startswith('disk_')
}
self._disk = disk(directory, **kwargs)
# Set cached attributes: updates settings and sets pragmas.
for key, value in sets.items():
query = 'INSERT OR REPLACE INTO Settings VALUES (?, ?)'
sql(query, (key, value))
self.reset(key, value)
for key, value in METADATA.items():
query = 'INSERT OR IGNORE INTO Settings VALUES (?, ?)'
sql(query, (key, value))
self.reset(key)
(self._page_size,), = sql('PRAGMA page_size').fetchall()
# Setup Cache table.
sql('CREATE TABLE IF NOT EXISTS Cache ('
' rowid INTEGER PRIMARY KEY,'
' key BLOB,'
' raw INTEGER,'
' store_time REAL,'
' expire_time REAL,'
' access_time REAL,'
' access_count INTEGER DEFAULT 0,'
' tag BLOB,'
' size INTEGER DEFAULT 0,'
' mode INTEGER DEFAULT 0,'
' filename TEXT,'
' value BLOB)'
)
sql('CREATE UNIQUE INDEX IF NOT EXISTS Cache_key_raw ON'
' Cache(key, raw)'
)
sql('CREATE INDEX IF NOT EXISTS Cache_expire_time ON'
' Cache (expire_time)'
)
query = EVICTION_POLICY[self.eviction_policy]['init']
if query is not None:
sql(query)
# Use triggers to keep Metadata updated.
sql('CREATE TRIGGER IF NOT EXISTS Settings_count_insert'
' AFTER INSERT ON Cache FOR EACH ROW BEGIN'
' UPDATE Settings SET value = value + 1'
' WHERE key = "count"; END'
)
sql('CREATE TRIGGER IF NOT EXISTS Settings_count_delete'
' AFTER DELETE ON Cache FOR EACH ROW BEGIN'
' UPDATE Settings SET value = value - 1'
' WHERE key = "count"; END'
)
sql('CREATE TRIGGER IF NOT EXISTS Settings_size_insert'
' AFTER INSERT ON Cache FOR EACH ROW BEGIN'
' UPDATE Settings SET value = value + NEW.size'
' WHERE key = "size"; END'
)
sql('CREATE TRIGGER IF NOT EXISTS Settings_size_update'
' AFTER UPDATE ON Cache FOR EACH ROW BEGIN'
' UPDATE Settings'
' SET value = value + NEW.size - OLD.size'
' WHERE key = "size"; END'
)
sql('CREATE TRIGGER IF NOT EXISTS Settings_size_delete'
' AFTER DELETE ON Cache FOR EACH ROW BEGIN'
' UPDATE Settings SET value = value - OLD.size'
' WHERE key = "size"; END'
)
# Create tag index if requested.
if self.tag_index: # pylint: disable=no-member
self.create_tag_index()
else:
self.drop_tag_index()
# Close and re-open database connection with given timeout.
self.close()
self._timeout = timeout
self._sql # pylint: disable=pointless-statement
@property
def directory(self):
"""Cache directory."""
return self._directory
@property
def timeout(self):
"""SQLite connection timeout value in seconds."""
return self._timeout
@property
def disk(self):
"""Disk used for serialization."""
return self._disk
@property
def _sql(self):
con = getattr(self._local, 'con', None)
if con is None:
con = self._local.con = sqlite3.connect(
op.join(self._directory, DBNAME),
timeout=self._timeout,
isolation_level=None,
)
# Some SQLite pragmas work on a per-connection basis so query the
# Settings table and reset the pragmas. The Settings table may not
# exist so catch and ignore the OperationalError that may occur.
try:
select = 'SELECT key, value FROM Settings'
settings = con.execute(select).fetchall()
except sqlite3.OperationalError:
pass
else:
for key, value in settings:
if key.startswith('sqlite_'):
self.reset(key, value, update=False)
return con.execute
@cl.contextmanager
def _transact(self, filename=None):
sql = self._sql
filenames = []
_disk_remove = self._disk.remove
try:
sql('BEGIN IMMEDIATE')
except sqlite3.OperationalError:
if filename is not None:
_disk_remove(filename)
raise Timeout
try:
yield sql, filenames.append
except BaseException:
sql('ROLLBACK')
raise
else:
sql('COMMIT')
for name in filenames:
if name is not None:
_disk_remove(name)
def set(self, key, value, expire=None, read=False, tag=None):
"""Set `key` and `value` item in cache.
When `read` is `True`, `value` should be a file-like object opened
for reading in binary mode.
:param key: key for item
:param value: value for item
:param float expire: seconds until item expires
(default None, no expiry)
:param bool read: read value as bytes from file (default False)
:param str tag: text to associate with key (default None)
:return: True if item was set
:raises Timeout: if database timeout expires
"""
now = time.time()
db_key, raw = self._disk.put(key)
expire_time = None if expire is None else now + expire
size, mode, filename, db_value = self._disk.store(value, read, key=key)
columns = (expire_time, tag, size, mode, filename, db_value)
# The order of SELECT, UPDATE, and INSERT is important below.
#
# Typical cache usage pattern is:
#
# value = cache.get(key)
# if value is None:
# value = expensive_calculation()
# cache.set(key, value)
#
# Cache.get does not evict expired keys to avoid writes during lookups.
# Commonly used/expired keys will therefore remain in the cache making
# an UPDATE the preferred path.
#
# The alternative is to assume the key is not present by first trying
# to INSERT and then handling the IntegrityError that occurs from
# violating the UNIQUE constraint. This optimistic approach was
# rejected based on the common cache usage pattern.
#
# INSERT OR REPLACE aka UPSERT is not used because the old filename may
# need cleanup.
with self._transact(filename) as (sql, cleanup):
rows = sql(
'SELECT rowid, filename FROM Cache'
' WHERE key = ? AND raw = ?',
(db_key, raw),
).fetchall()
if rows:
(rowid, old_filename), = rows
cleanup(old_filename)
self._row_update(rowid, now, columns)
else:
self._row_insert(db_key, raw, now, columns)
self._cull(now, sql, cleanup)
return True
__setitem__ = set
def _row_update(self, rowid, now, columns):
sql = self._sql
expire_time, tag, size, mode, filename, value = columns
sql('UPDATE Cache SET'
' store_time = ?,'
' expire_time = ?,'
' access_time = ?,'
' access_count = ?,'
' tag = ?,'
' size = ?,'
' mode = ?,'
' filename = ?,'
' value = ?'
' WHERE rowid = ?', (
now, # store_time
expire_time,
now, # access_time
0, # access_count
tag,
size,
mode,
filename,
value,
rowid,
),
)
def _row_insert(self, key, raw, now, columns):
sql = self._sql
expire_time, tag, size, mode, filename, value = columns
sql('INSERT INTO Cache('
' key, raw, store_time, expire_time, access_time,'
' access_count, tag, size, mode, filename, value'
') VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)', (
key,
raw,
now, # store_time
expire_time,
now, # access_time
0, # access_count
tag,
size,
mode,
filename,
value,
),
)
def _cull(self, now, sql, cleanup, limit=None):
cull_limit = self.cull_limit if limit is None else limit
if cull_limit == 0:
return
# Evict expired keys.
select_expired_template = (
'SELECT %s FROM Cache'
' WHERE expire_time IS NOT NULL AND expire_time < ?'
' ORDER BY expire_time LIMIT ?'
)
select_expired = select_expired_template % 'filename'
rows = sql(select_expired, (now, cull_limit)).fetchall()
if rows:
delete_expired = (
'DELETE FROM Cache WHERE rowid IN (%s)'
% (select_expired_template % 'rowid')
)
sql(delete_expired, (now, cull_limit))
for filename, in rows:
cleanup(filename)
cull_limit -= len(rows)
if cull_limit == 0:
return
# Evict keys by policy.
select_policy = EVICTION_POLICY[self.eviction_policy]['cull']
if select_policy is None or self.volume() < self.size_limit:
return
select_filename = select_policy.format(fields='filename', now=now)
rows = sql(select_filename, (cull_limit,)).fetchall()
if rows:
delete = (
'DELETE FROM Cache WHERE rowid IN (%s)'
% (select_policy.format(fields='rowid', now=now))
)
sql(delete, (cull_limit,))
for filename, in rows:
cleanup(filename)
def add(self, key, value, expire=None, read=False, tag=None):
"""Add `key` and `value` item to cache.
Similar to `set`, but only add to cache if key not present.
Operation is atomic. Only one concurrent add operation for a given key
will succeed.
When `read` is `True`, `value` should be a file-like object opened
for reading in binary mode.
:param key: key for item
:param value: value for item
:param float expire: seconds until the key expires
(default None, no expiry)
:param bool read: read value as bytes from file (default False)
:param str tag: text to associate with key (default None)
:return: True if item was added
:raises Timeout: if database timeout expires
"""
now = time.time()
db_key, raw = self._disk.put(key)
expire_time = None if expire is None else now + expire
size, mode, filename, db_value = self._disk.store(value, read, key=key)
columns = (expire_time, tag, size, mode, filename, db_value)
with self._transact(filename) as (sql, cleanup):
rows = sql(
'SELECT rowid, filename, expire_time FROM Cache'
' WHERE key = ? AND raw = ?',
(db_key, raw),
).fetchall()
if rows:
(rowid, old_filename, old_expire_time), = rows
if old_expire_time is None or old_expire_time > now:
cleanup(filename)
return False
cleanup(old_filename)
self._row_update(rowid, now, columns)
else:
self._row_insert(db_key, raw, now, columns)
self._cull(now, sql, cleanup)
return True
def incr(self, key, delta=1, default=0):
"""Increment value by delta for item with key.
If key is missing and default is None then raise KeyError. Else if key
is missing and default is not None then use default for value.
Operation is atomic. All concurrent increment operations will be
counted individually.
Assumes value may be stored in a SQLite column. Most builds that target
machines with 64-bit pointer widths will support 64-bit signed
integers.
:param key: key for item
:param int delta: amount to increment (default 1)
:param int default: value if key is missing (default None)
:return: new value for item
:raises KeyError: if key is not found and default is None
:raises Timeout: if database timeout expires
"""
now = time.time()
db_key, raw = self._disk.put(key)
select = (
'SELECT rowid, expire_time, filename, value FROM Cache'
' WHERE key = ? AND raw = ?'
)
with self._transact() as (sql, cleanup):
rows = sql(select, (db_key, raw)).fetchall()
if not rows:
if default is None:
raise KeyError(key)
value = default + delta
columns = (None, None) + self._disk.store(value, False, key=key)
self._row_insert(db_key, raw, now, columns)
self._cull(now, sql, cleanup)
return value
(rowid, expire_time, filename, value), = rows
if expire_time is not None and expire_time < now:
if default is None:
raise KeyError(key)
value = default + delta
columns = (None, None) + self._disk.store(value, False, key=key)
self._row_update(rowid, now, columns)
self._cull(now, sql, cleanup)
cleanup(filename)
return value
value += delta
columns = 'store_time = ?, value = ?'
update_column = EVICTION_POLICY[self.eviction_policy]['get']
if update_column is not None:
columns += ', ' + update_column.format(now=now)
update = 'UPDATE Cache SET %s WHERE rowid = ?' % columns
sql(update, (now, value, rowid))
return value
def decr(self, key, delta=1, default=0):
"""Decrement value by delta for item with key.
If key is missing and default is None then raise KeyError. Else if key
is missing and default is not None then use default for value.
Operation is atomic. All concurrent decrement operations will be
counted individually.
Unlike Memcached, negative values are supported. Value may be
decremented below zero.
Assumes value may be stored in a SQLite column. Most builds that target
machines with 64-bit pointer widths will support 64-bit signed
integers.
:param key: key for item
:param int delta: amount to decrement (default 1)
:param int default: value if key is missing (default 0)
:return: new value for item
:raises KeyError: if key is not found and default is None
:raises Timeout: if database timeout expires
"""
return self.incr(key, -delta, default)
def get(self, key, default=None, read=False, expire_time=False, tag=False):
"""Retrieve value from cache. If `key` is missing, return `default`.
:param key: key for item
:param default: value to return if key is missing (default None)
:param bool read: if True, return file handle to value
(default False)
:param bool expire_time: if True, return expire_time in tuple
(default False)
:param bool tag: if True, return tag in tuple (default False)
:return: value for item or default if key not found
:raises Timeout: if database timeout expires
"""
db_key, raw = self._disk.put(key)
update_column = EVICTION_POLICY[self.eviction_policy]['get']
select = (
'SELECT rowid, expire_time, tag, mode, filename, value'
' FROM Cache WHERE key = ? AND raw = ?'
' AND (expire_time IS NULL OR expire_time > ?)'
)
if expire_time and tag:
default = (default, None, None)
elif expire_time or tag:
default = (default, None)
if not self.statistics and update_column is None:
# Fast path, no transaction necessary.
rows = self._sql(select, (db_key, raw, time.time())).fetchall()
if not rows:
return default
(rowid, db_expire_time, db_tag, mode, filename, db_value), = rows
try:
value = self._disk.fetch(mode, filename, db_value, read)
except IOError as error:
if error.errno == errno.ENOENT:
# Key was deleted before we could retrieve result.
return default
else:
raise
else: # Slow path, transaction required.
cache_hit = (
'UPDATE Settings SET value = value + 1 WHERE key = "hits"'
)
cache_miss = (
'UPDATE Settings SET value = value + 1 WHERE key = "misses"'
)
with self._transact() as (sql, _):
rows = sql(select, (db_key, raw, time.time())).fetchall()
if not rows:
if self.statistics:
sql(cache_miss)
return default
(rowid, db_expire_time, db_tag,
mode, filename, db_value), = rows
try:
value = self._disk.fetch(mode, filename, db_value, read)
except IOError as error:
if error.errno == errno.ENOENT:
# Key was deleted before we could retrieve result.
if self.statistics:
sql(cache_miss)
return default
else:
raise
if self.statistics:
sql(cache_hit)
now = time.time()
update = 'UPDATE Cache SET %s WHERE rowid = ?'
if update_column is not None:
sql(update % update_column.format(now=now), (rowid,))
if expire_time and tag:
return (value, db_expire_time, db_tag)
elif expire_time:
return (value, db_expire_time)
elif tag:
return (value, db_tag)
else:
return value
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