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58 lines
1.8 KiB
58 lines
1.8 KiB
# -*- encoding: utf-8 -*-
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from __future__ import absolute_import, unicode_literals
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import time
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from . import Base
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class SQLite3Cache(Base):
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"""Implements a shared cache using SQLite3. Works across multiple processes
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and threads, concurrent writes are not supported.
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JSON is used to serialize python primitives in a safe way.
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"""
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serialize = True
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def __init__(self, connection, threshold=1024, timeout=-1):
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super(SQLite3Cache, self).__init__(threshold, timeout)
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self.connection = connection
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self.connection.execute(
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'CREATE TABLE IF NOT EXISTS cache ('
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' key TEXT PRIMARY KEY,'
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' value BLOB,'
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' time FLOAT)')
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# drop trigger, in case threshold has changed
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self.connection.execute('DROP TRIGGER IF EXISTS sweeper')
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self.connection.execute([
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'CREATE TRIGGER sweeper AFTER INSERT ON cache',
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'BEGIN',
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' DELETE FROM cache WHERE key NOT IN ('
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' SELECT key FROM cache',
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' ORDER BY time DESC LIMIT {0}'.format(threshold),
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' );',
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'END'])
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def _get(self, ns, key, default=None):
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rv = self.connection.execute(
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'SELECT value FROM cache WHERE key = ?',
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(ns + b'-' + key, )).fetchone()
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if rv is None:
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raise KeyError
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return rv[0]
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def _set(self, ns, key, value):
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with self.connection.transaction as con:
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con.execute(
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'INSERT OR REPLACE INTO cache (key, value, time) VALUES (?, ?, ?)',
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(ns + b'-' + key, value, time.time()))
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def _delete(self, ns, key):
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with self.connection.transaction as con:
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con.execute('DELETE FROM cache WHERE key = ?', (ns + b'-' + key, ))
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