questions about listing 2.9
KayWu opened this issue · comments
# listing 2.9
def update_token(conn, token, user, item=None):
timestamp = time.time()
conn.hset('login:', token, user)
conn.zadd('recent:', token, timestamp)
if item:
conn.zadd('viewed:' + token, item, timestamp)
conn.zremrangebyrank('viewed:' + token, 0, -26)
conn.zincrby('viewed:', item, -1)
conn.zincrby('viewed:', item, -1) means more views will lead to a lower score.
# listing 2.10
def rescale_viewed(conn):
while not QUIT:
conn.zremrangebyrank('viewed:', 0, -20001)
conn.zinterstore('viewed:', {'viewed:': .5})
time.sleep(300)
conn.zremrangebyrank('viewed:', 0, -20001) will keep the last 20000 items，
The order is from small to big, so items with few views will get a high score and be kept.
Guess conn.zincrby('viewed:', item, 1) or conn.zremrangebyrank('viewed:', 20001, -1) will work.
I was going to say, "known errata, fixed years ago". Then I looked again.
Let's go through this piece by piece. Everything viewed gets ZINCRBY -1; so if something is seen 1000000 times, they will have a score of -1000000. If something is seen 10 times, it will have a score of -10. So the "highest viewed items" will be at index 0, and the lowest viewed items will be at index -1.
In listing 2.10, the old code (from before 2014-05-04) read:
def rescale_viewed(conn):
while not QUIT:
conn.zremrangebyrank('viewed:', 20000, -1)
conn.zinterstore('viewed:', {'viewed:': .5})
time.sleep(300)
Which deleted things at index 20k to -1, so items with the lowest actual views. On 2014.-05-04, I took a correction from someone, because apparently I wasn't reading my own code, and turned that into what you see above:
def rescale_viewed(conn):
while not QUIT:
conn.zremrangebyrank('viewed:', 0, -20001)
conn.zinterstore('viewed:', {'viewed:': .5})
time.sleep(300)
... which deletes everything except the least-used 20k items. You are right.
I'm going to switch the code back, update the errata, and get back to you. Thank you.
Okay, updated the code and errata in this changelog: 691bebe
You can see it live: https://htmlpreview.github.io/?https://github.com/josiahcarlson/redis-in-action/blob/master/excerpt_errata.html#l2.10
Thank you for the question!