平武建站

Redis内存诡异增长如何排查问题

这篇文章给大家分享的是有关redis内存诡异增长如何排查问题的内容。小编觉得挺实用的，因此分享给大家做个参考，一起跟随小编过来看看吧。

创新互联是一家以重庆网站建设公司、网页设计、品牌设计、软件运维、成都网站营销、小程序App开发等移动开发为一体互联网公司。已累计为酒店设计等众行业中小客户提供优质的互联网建站和软件开发服务。

一、现象

实例名：r-bp1cxxxxxxxxxd04(主从)

问题：一分钟内存上涨了2G，如下图所示：

键值规模：6000万左右

内存一分钟增长2G.png

Redis内存诡异增长如何排查问题

二、Redis内存分析

1. 内存组成

上图中的内存统计的是Redis的info memory命令中的used_memory属性，例如：

redis>infomemory#Memoryused_memory:9195978072used_memory_human:8.56Gused_memory_rss:9358786560used_memory_peak:10190212744used_memory_peak_human:9.49Gused_memory_lua:38912mem_fragmentation_ratio:1.02mem_allocator:jemalloc-3.6.0

每个属性的详细说明

属性名属性说明
used_memoryRedis 分配器分配的内存量，也就是实际存储数据的内存总量
used_memory_human以可读格式返回 Redis 使用的内存总量
used_memory_rss从操作系统的角度，Redis进程占用的总物理内存
used_memory_peak内存分配器分配的最大内存，代表used_memory的历史峰值
used_memory_peak_human以可读的格式显示内存消耗峰值
used_memory_luaLua引擎所消耗的内存
mem_fragmentation_ratioused_memory_rss /used_memory比值，表示内存碎片率
mem_allocatorRedis 所使用的内存分配器。默认: jemalloc

计算公式如下：

used_memory = 自身内存+对象内存+缓冲内存+lua内存used_rss = used_memory + 内存碎片

如下图所示：

Redis内存诡异增长如何排查问题

2. 内存分析

(1) 自身内存：一个空的Redis占用很小，可以忽略不计

(2) kv内存：key对象 + value对象

(3) 缓冲区：客户端缓冲区(普通 + slave伪装 + pubsub)以及aof缓冲区(比较固定，一般没问题)

(4) Lua：Lua引擎所消耗的内存

3. 内存突增常见问题

(1) kv内存：bigkey、大量写入

(2) 客户端缓冲区：一般常见的有普通客户端缓冲区(例如monitor命令)或者pubsub客户端缓冲区

三、问题排查

(1) bigkey ? 经扫描未发现bigkey

Sampled 67234427 keys in the keyspace!
Total key length in bytes is 1574032382 (avg len 23.41)

Biggest string found 'CCARD_DEVICE_CARD_REF_MAP_KEY_016817000004209' has 20862 bytes
Biggest list found 'CCARD_VALID_DEVICE_TRAIN_QUEUE_KEY' has 51 items
Biggest hash found 'CCARD_VALID_DEVICE_TRAIN_MAP_KEY' has 51 fields

67234359 strings with 71767890 bytes (100.00% of keys, avg size 1.07)
67 lists with 151 items (00.00% of keys, avg size 2.25)
0 sets with 0 members (00.00% of keys, avg size 0.00)
1 hashs with 51 fields (00.00% of keys, avg size 51.00)
0 zsets with 0 members (00.00% of keys, avg size 0.00)

(2) 键值个数增加？未发现键值有明显变化

Redis内存诡异增长如何排查问题

(3) 客户端缓冲区

由于内存增上去后，长时间没下落，如果是因为缓冲区问题，会从info clients找到明显问题，执行后发现：

redis> info clients
# Clients
connected_clients:43
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0
admin_clients:6
rejected_vpc_conn_count:0
close_idle_unknown_conn_count:0

执行client中也没有明显的omem大于0的情况

id=80207addr=10.xx.0.4:63920fd=46name=age=624idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80215addr=10.xx.0.23:43489fd=36name=age=591idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80366addr=10.xx.0.8:59785fd=18name=age=84idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=delread=0write=0type=user
id=80356addr=10.xx.0.33:32117fd=13name=age=114idle=0flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80064addr=10.xx.59.4:53446fd=38name=age=1070idle=1070flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=NULL read=0write=0type=admin
id=80276addr=10.xx.0.23:48511fd=8name=age=387idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80188addr=10.xx.0.33:16265fd=42name=age=681idle=3flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80326addr=10.xx.0.32:59779fd=16name=age=209idle=0flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80065addr=10.xx.59.4:53447fd=45name=age=1070idle=1070flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=NULL read=0write=0type=admin
id=79936addr=10.xx.0.22:10607fd=30name=age=1480idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80174addr=10.xx.0.5:60914fd=6name=age=722idle=2flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80300addr=10.xx.0.22:22757fd=48name=age=298idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80037addr=10.xx.0.5:55189fd=15name=age=1143idle=2flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80330addr=10.xx.0.8:48533fd=17name=age=199idle=10flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=79896addr=10.xx.0.30:26814fd=11name=age=1616idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80299addr=10.xx.0.24:11227fd=44name=age=303idle=3flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80086addr=10.xx.0.32:52526fd=40name=age=1002idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80202addr=10.xx.0.33:16658fd=26name=age=636idle=3flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80256addr=10.xx.0.24:60496fd=19name=age=448idle=2flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=79908addr=10.xx.0.29:18975fd=12name=age=1583idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80365addr=10.xx.0.29:46429fd=14name=age=85idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=79869addr=10.xx.27.4:48455fd=35name=age=1700idle=1700flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=NULL read=0write=0type=admin
id=80334addr=10.xx.0.23:50012fd=39name=age=189idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80041addr=10.xx.0.32:51107fd=33name=age=1132idle=3flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=79992addr=10.xx.0.22:12068fd=28name=age=1289idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80251addr=10.xx.0.30:44213fd=23name=age=468idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80006addr=10.xx.0.2:45895fd=31name=age=1242idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80321addr=10.xx.0.30:48048fd=5name=age=224idle=3flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80381addr=10.xx.0.8:13360fd=22name=age=24idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=delread=0write=0type=user
id=80200addr=10.xx.0.24:59183fd=24name=age=640idle=0flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80113addr=10.xx.0.2:52492fd=21name=age=915idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=174addr=11.216.117.242:53027fd=9name=age=281390idle=0flags=S db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=replconf read=0write=0type=admin
id=79991addr=10.xx.0.4:48412fd=25name=age=1296idle=0flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80301addr=127.0.0.1:47869fd=49name=age=291idle=261flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=strlen read=0write=0type=admin
id=80047addr=10.xx.59.4:53184fd=41name=age=1114idle=1114flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=NULL read=0write=0type=admin
id=80236addr=10.xx.0.5:62546fd=47name=age=516idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80364addr=10.xx.0.4:18794fd=7name=age=85idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80175addr=10.xx.0.4:62245fd=29name=age=718idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80336addr=10.xx.0.29:45701fd=50name=age=180idle=1flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80050addr=10.xx.59.4:53188fd=43name=age=1114idle=1114flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=NULL read=0write=0type=admin
id=79765addr=10.xx.0.2:33832fd=37name=age=2027idle=177flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=info read=0write=0type=user
id=80170addr=10.xx.0.2:57853fd=20name=age=728idle=24flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=0obl=0oll=0omem=0events=r cmd=ping read=0write=0type=user
id=80390addr=127.0.0.1:49449fd=27name=age=0idle=0flags=N db=0sub=0psub=0multi=-1qbuf=0qbuf-free=32768obl=0oll=0omem=0events=r cmd=client read=0write=0type=admin

四、揪出元凶

常用的几招都用了，还是不行，同事@径远帮忙一起分析，怀疑是不是因为Redis的kv哈希表做了 rehash。

1. Redis的kv存储结构

如下图所示，Redis的所有kv保存在dict中，其中ht对应两个哈希表ht[0]和ht[1]，平时一个空闲，一个用于存储数据，只有当需要rehash时，ht[1]才会用到。

Redis内存诡异增长如何排查问题

2. Redis的字典rehash

为了保证哈希表的负载，当哈希表的元素个数等于哈希表槽数时候，会进行rehash扩容。扩容后h[1]的容量等于第一个大于等于ht[0].size*2的2n，例如hash表的初始化容量是4，那么下一次扩容就是8，以此类推。

3. 测试

(1) 测试方法

先批量写入到rehash阈值附近，然后在逐条去写，观察内存变化

// 为每个键设置1天过期时间
int expireTime = 60 * 60 * 24;
// rehash阈值 - 50为了方便观察rehash内存变化
int rehashThreshold = (int) Math.pow(2, 25) - 50;

// 1.批量写入：pipeline批量写入，由于是本机测试，这里用10000，实际生产不要这么用
Pipeline pipeline = jedis.pipelined();
pipeline = jedis.pipelined();
for (int i = 0; i < rehashThreshold; i++) {
  pipeline.setex(String.valueOf(i), expireTime, String.valueOf(i));
  if (i % 10000 == 0) {
    pipeline.sync();
  }
}
pipeline.sync();

// 2.等待写增量
TimeUnit.SECONDS.sleep(5);
for (int i = rehashThreshold; i < rehashThreshold + 200; i++) {
  jedis.setex(String.valueOf(i), expireTime, String.valueOf(i));
  TimeUnit.SECONDS.sleep(1);
}

(2) 开始测试

(a) 当阈值=215=32768，从下面可以看出到key的个数为32769时，内存涨了一些，但是还不明显。

keys       mem      clients blocked requests            connections32766      4.69M    3       0       32797 (+2)          4
32767      4.69M    3       0       32799 (+2)          4
32768      4.69M    3       0       32801 (+2)          4
32769      5.44M    3       0       32803 (+2)          4

(b) 当阈值=220=1048576，从下面可以看出到key的个数为1048577时，内存涨了32M。因为rehash会扩容，所以新的哈希表中的槽位变为了221 * 2（因为每个key都设置了过期时间，expires表），指针为8个字节，221 ? 2 ? 8 = 225 = 32MB。

keys       mem      clients blocked requests            connections1048574    128.69M  3       0       3364129 (+2)        16
1048575    128.69M  3       0       3364131 (+2)        16
1048576    128.69M  3       0       3364133 (+2)        16
1048577    160.69M  3       0       3364135 (+2)        16
1048578    160.69M  3       0       3364137 (+2)        16

(c) 当阈值=226=67108864，从下面可以看出到key的个数为67108865时，内存涨了2GB。因为rehash会扩容，所以新的哈希表中的槽位变为了227 * 2（因为每个key都设置了过期时间，expires表），指针为8个字节，227 ? 2 ? 8 = 231 = 2GB。

keys       mem      clients blocked requests            connections67108862   9.70G    3       0       70473683 (+2)       18
67108863   9.70G    3       0       70473685 (+2)       18
67108864   9.70G    3       0       70473687 (+2)       18
67108865   11.70G   3       0       70473689 (+2)       18
67108866   11.70G   3       0       70473691 (+2)       18
67108867   11.70G   3       0       70473693 (+2)       18

回过来看r-bp1c15fd9b142d04的key和内存变化图，可以发现上面的规则是正确的：

 Redis内存诡异增长如何排查问题

4. 后续观察

17点时，rehash结束，内存降了增加的2G的一半。

Redis内存诡异增长如何排查问题

感谢各位的阅读！关于“Redis内存诡异增长如何排查问题”这篇文章就分享到这里了，希望以上内容可以对大家有一定的帮助，让大家可以学到更多知识，如果觉得文章不错，可以把它分享出去让更多的人看到吧！


分享文章：Redis内存诡异增长如何排查问题
网页URL：http://pwwzsj.com/article/ggpdsp.html

其他资讯