First, let’s look at a scenario: a website needs to count users who have logged in continuously within a week, and users who have logged in within a month.
If it is implemented using a traditional database such as Mysql, it will be difficult to achieve. But if you use Redis to do it, it is very simple. Redis's collection type and Bitmap type can be easily achieved. Today, we will mainly talk about how to use Bitmaps to implement the function of counting active users.
Bitmaps
In a computer system, the smallest unit of information is a byte. 1 byte is equal to 8 bits. Each bit It can only be 0 or 1 (the computer only knows these two numbers). Bitmaps allow direct manipulation of bits.
Bigmaps can be regarded as an array. Each bit in the array can only be 0 or 1. The subscript of the array is regarded as an offset here.
Let’s introduce a few commands related to Bitmaps:
setbit
##setbit key offset value: Set the value for the corresponding bit
For example, if users 3, 8, 23, and 32 visited the website today, thensetbit user:view:2020-5-17 3 1 setbit user:view:2020-5-17 8 1 setbit user:view:2020-5-17 23 1 setbit user:view:2020-5-17 32 1
Development tips : Many application IDs do not start from 1, but many start from a specified number, such as 1001, 10001. For these, we can subtract the initial value when setting to prevent wasting space
getbit
##getbit key offset gets the value of the specified bitIf I want to know whether user No. 8 and user No. 45 have logged in today, then
127.0.0.1:6379> getbit user:view:2020-5-17 8 (integer) 1 127.0.0.1:6379> getbit user:view:2020-5-17 45 (integer) 0
I can see that user No. 8 has logged in today, But user No. 45 has not logged in today.
bitcount
bitcount key [start] [end] Get the number in the specified range of 1I want to know how many users have logged in today, then
127.0.0.1:6379> bitcount user:view:2020-5-17 (integer) 4
Operation between Bitmaps
bitop op destkey key [key ...]The bitop command can perform intersection (and), union (or), non (not), exclusive or (xor) on multiple bitmaps, and the operation results Stored in destkey.
If you want to know the number of users who logged in for three consecutive days, that is, the number of users who logged in on May 17th, 18th, and 19th.
The login situation in the past three days is as follows:
127.0.0.1:6379> bitop and three:and user:view:2020-5-17 user:view:2020-5-18 user:view:2020-5-19 127.0.0.1:6379> bitcount three:and (integer) 2
127.0.0.1:6379> bitop or three:or user:view:2020-5-17 user:view:2020-5-18 user:view:2020-5-19 (integer) 10 127.0.0.1:6379> bitcount three:or (integer) 9
As you can see, a total of 9 users have logged in in the past three days.
Practical combatAfter finishing the above knowledge, we can complete the desired requirement: we need to count the number of consecutive logins within a week users, and users who have logged in within a month.
First simulate the user login situation within 30 days. The pseudo code is as follows:
for ($i = 0; $i < 20000; $i++) { $userId = mt_rand(1, 10000); $date = time() - 86400 * mt_rand(0, 30); $key = 'userlogin_'.date('Ymd', $date); $redis->setBit($key, $userId, 1); }
Get the users who have logged in within a week. Of course, we will not fetch them all at once, but we want to fetch them all at once like paging. A certain number, the pseudo code is as follows:
for ($i = 1; $i <= 7; $i ++) { $key = "userlogin_".date('Ymd', time() - (86400*$i)); if ($i == 1) { $redis->bitOp('and', 'week_logined', $key); } else { $redis->bitOp('and', 'week_logined', 'week_logined', $key); } } // 获取前50个用户 $userIds = []; for ($i=1; $i<=10000; $i++) { $ret = $redis->getBit('week_logined', $i); $ret && $userIds[] = $i; if (count($userIds) >=50) break; }
To obtain the users who logged in within a month, the idea is basically the same as above, except that the and is changed to or
for ($i = 1; $i <= 3; $i ++) { $key = "userlogin_".date('Ymd', time() - (86400*$i)); $redis->bitOp('or', 'month_loginOnce', 'month_loginOnce', $key); } // 获取一个月内登陆过的用户 $userIds = []; for ($i=1; $i<=10000; $i++) { $ret = $redis->getBit('month_loginOnce', $i); $ret && $userIds[] = $i; }
As you can see, there are still some differences between doing or and and. of. or, there is no need to judge the first time. The reason is for everyone to understand.
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