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84 lines
2.1 KiB
84 lines
2.1 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 sqlalchemy import Table, Column, MetaData, create_engine
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from sqlalchemy import Float, String, LargeBinary
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from sqlalchemy.sql import select, func
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from . import Base
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def get(con, cache, key):
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rv = con.execute(
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select([cache.c.value]).where(
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cache.c.key == 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(con, cache, key, value, threshold):
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cnt = con.execute(
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select([func.count(cache)])).fetchone()[0]
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if cnt + 1 > threshold:
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con.execute(
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cache.delete().where(
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cache.c.key.in_(select(
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[cache.c.key])
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.order_by(cache.c.time)
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.limit(1))))
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try:
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get(con, cache, key)
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except KeyError:
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insert = True
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else:
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insert = False
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if insert:
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stmt = cache.insert().values(key=key, value=value, time=time.time())
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else:
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stmt = cache.update().values(value=value, time=time.time()) \
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.where(cache.c.key == key)
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con.execute(stmt)
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def delete(con, cache, key):
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con.execute(cache.delete(cache.c.key == key))
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class SACache(Base):
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"""Implements cache using SQLAlchemy Core.
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"""
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serialize = True
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def __init__(self, db, threshold=1024, timeout=-1):
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super(SACache, self).__init__(threshold, timeout)
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self.metadata = MetaData()
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self.engine = create_engine(db)
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self.cache = Table("cache", self.metadata,
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Column("key", String(255), primary_key=True),
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Column("value", LargeBinary(65535)),
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Column("time", Float))
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self.metadata.create_all(self.engine)
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self.engine.execute(self.cache.delete())
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def _get(self, ns, key):
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return get(self.engine.connect(), self.cache, ns + b'-' + key)
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def _set(self, ns, key, value):
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set(self.engine.connect(), self.cache, ns + b'-' + key, value, self.threshold)
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def _delete(self, ns, key):
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delete(self.engine.connect(), self.cache, ns + b'-' + key)
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