[redis] redis配置中的save引起rdb快照生成的规则-摩杜云开发者社区

分析redis配置中的save, 具体是以何种规则来触发生成rdb.

redis配置中的注释:

#
# Save the DB on disk:
#
#   save <seconds> <changes>
#
#   Will save the DB if both the given number of seconds and the given
#   number of write operations against the DB occurred.
#
#   In the example below the behaviour will be to save:
#   after 900 sec (15 min) if at least 1 key changed
#   after 300 sec (5 min) if at least 10 keys changed
#   after 60 sec if at least 10000 keys changed
#
#   Note: you can disable saving completely by commenting out all "save" lines.
#
#   It is also possible to remove all the previously configured save
#   points by adding a save directive with a single empty string argument
#   like in the following example:
#
#   save ""

save 900 1
save 300 10
save 60 10000

解释下:

save后边有两个参数:

第一个参数是以秒为单位的周期
第二个参数是该周期内key的变动次数

如果在该周期到达时, key的变动次数达到第二个配置参数的值, 则触发rdb生成.

否则开始新的周期, 上个周期内变动的key的数量, 算作新周期内key的数量.

比如:

设置 save 5 3

以5秒为周期, key的变动次数为3.

第一个5秒的周期, 设置了2个key, 那么不会触发rdb生成.
随后的5秒的周期内, 因为上一个周期没有生成rdb, 所以上一个统计周期的key的变动次数2, 记录进本周期. 本周期只要有1个key变动, 则触发rdb生成

测试:

配置 save 5 3

测试脚本:

#!/bin/bash

RDB=./7000/dump.rdb

echo du -b $RDB
du -b $RDB

echo redis-cli -p 7000 set k1 v1
redis-cli -p 7000 set k1 v1

echo redis-cli -p 7000 set k2 v2
redis-cli -p 7000 set k2 v2

echo du -b $RDB
du -b $RDB

echo sleep 7s
sleep 7s

echo du -b $RDB
du -b $RDB

echo redis-cli -p 7000 set k3 v3
redis-cli -p 7000 set k3 v3

echo du -b $RDB
du -b $RDB

echo sleep 1s
sleep 1s

echo du -b $RDB
du -b $RDB

echo '------------------------------'


echo redis-cli -p 7000 set k4 v4
redis-cli -p 7000 set k4 v4

echo redis-cli -p 7000 set k5 v5
redis-cli -p 7000 set k5 v5

echo du -b $RDB
du -b $RDB

echo sleep 1s
sleep 1s

echo du -b $RDB
du -b $RDB

echo redis-cli -p 7000 set k6 v6
redis-cli -p 7000 set k6 v6

echo du -b $RDB
du -b $RDB

echo sleep 1s
sleep 1s

echo du -b $RDB
du -b $RDB

echo sleep 3s
sleep 3s

echo du -b $RDB
du -b $RDB

执行结果:

du -b ./7000/dump.rdb
176 ./7000/dump.rdb
redis-cli -p 7000 set k1 v1
OK
redis-cli -p 7000 set k2 v2
OK
du -b ./7000/dump.rdb
176 ./7000/dump.rdb
sleep 7s
du -b ./7000/dump.rdb
176 ./7000/dump.rdb
redis-cli -p 7000 set k3 v3
OK
du -b ./7000/dump.rdb
176 ./7000/dump.rdb
sleep 1s
du -b ./7000/dump.rdb
202 ./7000/dump.rdb
------------------------------
redis-cli -p 7000 set k4 v4
OK
redis-cli -p 7000 set k5 v5
OK
du -b ./7000/dump.rdb
202 ./7000/dump.rdb
sleep 1s
du -b ./7000/dump.rdb
202 ./7000/dump.rdb
redis-cli -p 7000 set k6 v6
OK
du -b ./7000/dump.rdb
202 ./7000/dump.rdb
sleep 1s
du -b ./7000/dump.rdb
202 ./7000/dump.rdb
sleep 3s
du -b ./7000/dump.rdb
224 ./7000/dump.rdb

结论:

save配置的时间周期内, 如果key变动数量没到达, 则进入下一个周期累计
如果save配置的时间周期内, key的变动数量到达, 但是没到达时间周期, 依然不会触发rdb生成. 必须要等到周期结束的时间点才会生成.