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 | "Database cache backend."
import base64
import pickle
from datetime import datetime
from django.conf import settings
from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
from django.db import DatabaseError, connections, models, router, transaction
from django.utils import timezone
class Options:
"""A class that will quack like a Django model _meta class.
This allows cache operations to be controlled by the router
"""
def __init__(self, table):
self.db_table = table
self.app_label = 'django_cache'
self.model_name = 'cacheentry'
self.verbose_name = 'cache entry'
self.verbose_name_plural = 'cache entries'
self.object_name = 'CacheEntry'
self.abstract = False
self.managed = True
self.proxy = False
self.swapped = False
class BaseDatabaseCache(BaseCache):
def __init__(self, table, params):
super().__init__(params)
self._table = table
class CacheEntry:
_meta = Options(table)
self.cache_model_class = CacheEntry
class DatabaseCache(BaseDatabaseCache):
# This class uses cursors provided by the database connection. This means
# it reads expiration values as aware or naive datetimes, depending on the
# value of USE_TZ and whether the database supports time zones. The ORM's
# conversion and adaptation infrastructure is then used to avoid comparing
# aware and naive datetimes accidentally.
pickle_protocol = pickle.HIGHEST_PROTOCOL
def get(self, key, default=None, version=None):
return self.get_many([key], version).get(key, default)
def get_many(self, keys, version=None):
if not keys:
return {}
key_map = {}
for key in keys:
self.validate_key(key)
key_map[self.make_key(key, version)] = key
db = router.db_for_read(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute(
'SELECT %s, %s, %s FROM %s WHERE %s IN (%s)' % (
quote_name('cache_key'),
quote_name('value'),
quote_name('expires'),
table,
quote_name('cache_key'),
', '.join(['%s'] * len(key_map)),
),
list(key_map),
)
rows = cursor.fetchall()
result = {}
expired_keys = []
expression = models.Expression(output_field=models.DateTimeField())
converters = (connection.ops.get_db_converters(expression) + expression.get_db_converters(connection))
for key, value, expires in rows:
for converter in converters:
expires = converter(expires, expression, connection)
if expires < timezone.now():
expired_keys.append(key)
else:
value = connection.ops.process_clob(value)
value = pickle.loads(base64.b64decode(value.encode()))
result[key_map.get(key)] = value
self._base_delete_many(expired_keys)
return result
def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
self._base_set('set', key, value, timeout)
def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
return self._base_set('add', key, value, timeout)
def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
return self._base_set('touch', key, None, timeout)
def _base_set(self, mode, key, value, timeout=DEFAULT_TIMEOUT):
timeout = self.get_backend_timeout(timeout)
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute("SELECT COUNT(*) FROM %s" % table)
num = cursor.fetchone()[0]
now = timezone.now()
now = now.replace(microsecond=0)
if timeout is None:
exp = datetime.max
elif settings.USE_TZ:
exp = datetime.utcfromtimestamp(timeout)
else:
exp = datetime.fromtimestamp(timeout)
exp = exp.replace(microsecond=0)
if num > self._max_entries:
self._cull(db, cursor, now)
pickled = pickle.dumps(value, self.pickle_protocol)
# The DB column is expecting a string, so make sure the value is a
# string, not bytes. Refs #19274.
b64encoded = base64.b64encode(pickled).decode('latin1')
try:
# Note: typecasting for datetimes is needed by some 3rd party
# database backends. All core backends work without typecasting,
# so be careful about changes here - test suite will NOT pick
# regressions.
with transaction.atomic(using=db):
cursor.execute(
'SELECT %s, %s FROM %s WHERE %s = %%s' % (
quote_name('cache_key'),
quote_name('expires'),
table,
quote_name('cache_key'),
),
[key]
)
result = cursor.fetchone()
if result:
current_expires = result[1]
expression = models.Expression(output_field=models.DateTimeField())
for converter in (connection.ops.get_db_converters(expression) +
expression.get_db_converters(connection)):
current_expires = converter(current_expires, expression, connection)
exp = connection.ops.adapt_datetimefield_value(exp)
if result and mode == 'touch':
cursor.execute(
'UPDATE %s SET %s = %%s WHERE %s = %%s' % (
table,
quote_name('expires'),
quote_name('cache_key')
),
[exp, key]
)
elif result and (mode == 'set' or (mode == 'add' and current_expires < now)):
cursor.execute(
'UPDATE %s SET %s = %%s, %s = %%s WHERE %s = %%s' % (
table,
quote_name('value'),
quote_name('expires'),
quote_name('cache_key'),
),
[b64encoded, exp, key]
)
elif mode != 'touch':
cursor.execute(
'INSERT INTO %s (%s, %s, %s) VALUES (%%s, %%s, %%s)' % (
table,
quote_name('cache_key'),
quote_name('value'),
quote_name('expires'),
),
[key, b64encoded, exp]
)
else:
return False # touch failed.
except DatabaseError:
# To be threadsafe, updates/inserts are allowed to fail silently
return False
else:
return True
def delete(self, key, version=None):
self.validate_key(key)
return self._base_delete_many([self.make_key(key, version)])
def delete_many(self, keys, version=None):
key_list = []
for key in keys:
self.validate_key(key)
key_list.append(self.make_key(key, version))
self._base_delete_many(key_list)
def _base_delete_many(self, keys):
if not keys:
return False
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
table = quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute(
'DELETE FROM %s WHERE %s IN (%s)' % (
table,
quote_name('cache_key'),
', '.join(['%s'] * len(keys)),
),
keys,
)
return bool(cursor.rowcount)
def has_key(self, key, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
db = router.db_for_read(self.cache_model_class)
connection = connections[db]
quote_name = connection.ops.quote_name
if settings.USE_TZ:
now = datetime.utcnow()
else:
now = datetime.now()
now = now.replace(microsecond=0)
with connection.cursor() as cursor:
cursor.execute(
'SELECT %s FROM %s WHERE %s = %%s and expires > %%s' % (
quote_name('cache_key'),
quote_name(self._table),
quote_name('cache_key'),
),
[key, connection.ops.adapt_datetimefield_value(now)]
)
return cursor.fetchone() is not None
def _cull(self, db, cursor, now):
if self._cull_frequency == 0:
self.clear()
else:
connection = connections[db]
table = connection.ops.quote_name(self._table)
cursor.execute("DELETE FROM %s WHERE expires < %%s" % table,
[connection.ops.adapt_datetimefield_value(now)])
cursor.execute("SELECT COUNT(*) FROM %s" % table)
num = cursor.fetchone()[0]
if num > self._max_entries:
cull_num = num // self._cull_frequency
cursor.execute(
connection.ops.cache_key_culling_sql() % table,
[cull_num])
last_cache_key = cursor.fetchone()
if last_cache_key:
cursor.execute(
'DELETE FROM %s WHERE cache_key < %%s' % table,
[last_cache_key[0]],
)
def clear(self):
db = router.db_for_write(self.cache_model_class)
connection = connections[db]
table = connection.ops.quote_name(self._table)
with connection.cursor() as cursor:
cursor.execute('DELETE FROM %s' % table)
|