Redis okresowo przestaje odpowiadać przy dużym obciążeniu.

Question

Korzystam z prostej konfiguracji serwera redis do przechowywania niektórych wartości w mojej aplikacji PHP. Wczoraj instaluję moduł phpredis, aby użyć redis jako zaplecza PHP Session, co zwiększyło szybkość żądania dla DB redlic DB od 100 do 2000, a rozmiar DB z 60Mb do 200Mb.

Po tym wszystkim, redis nie jest dostępny na każde 10 żądanie - po prostu nie odpowiada. Plik dziennika nie pokazuje niczego, co mogłoby to wyjaśnić.

Mam ponad 50% wolnej pamięci. Oto zasoby używane przez redis:

PID USER  PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND                    
31075 root  20 0 170m 161m 936 S 41 2.0 11:10.52 redis-server 

Co może być tego przyczyną? Może powinienem poprawić niektóre ustawienia redis dla większego obciążenia?

Oto moja redis.conf:

# Redis configuration file example 

# Note on units: when memory size is needed, it is possible to specifiy 
# it in the usual form of 1k 5GB 4M and so forth: 
# 
# 1k => 1000 bytes 
# 1kb => 1024 bytes 
# 1m => 1000000 bytes 
# 1mb => 1024*1024 bytes 
# 1g => 1000000000 bytes 
# 1gb => 1024*1024*1024 bytes 
# 
# units are case insensitive so 1GB 1Gb 1gB are all the same. 

# By default Redis does not run as a daemon. Use 'yes' if you need it. 
# Note that Redis will write a pid file in /var/run/redis.pid when daemonized. 
daemonize no 

# When running daemonized, Redis writes a pid file in /var/run/redis.pid by 
# default. You can specify a custom pid file location here. 
pidfile /var/run/redis.pid 

# Accept connections on the specified port, default is 6379. 
# If port 0 is specified Redis will not listen on a TCP socket. 
port 6379 

# If you want you can bind a single interface, if the bind option is not 
# specified all the interfaces will listen for incoming connections. 
# 
# bind 127.0.0.1 

# Specify the path for the unix socket that will be used to listen for 
# incoming connections. There is no default, so Redis will not listen 
# on a unix socket when not specified. 
# 
# unixsocket /tmp/redis.sock 

# Close the connection after a client is idle for N seconds (0 to disable) 
timeout 300 

# Set server verbosity to 'debug' 
# it can be one of: 
# debug (a lot of information, useful for development/testing) 
# verbose (many rarely useful info, but not a mess like the debug level) 
# notice (moderately verbose, what you want in production probably) 
# warning (only very important/critical messages are logged) 
loglevel debug 

# Specify the log file name. Also 'stdout' can be used to force 
# Redis to log on the standard output. Note that if you use standard 
# output for logging but daemonize, logs will be sent to /dev/null 
logfile /var/log/redis/redis.log 

# To enable logging to the system logger, just set 'syslog-enabled' to yes, 
# and optionally update the other syslog parameters to suit your needs. 
# syslog-enabled no 

# Specify the syslog identity. 
# syslog-ident redis 

# Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7. 
# syslog-facility local0 

# Set the number of databases. The default database is DB 0, you can select 
# a different one on a per-connection basis using SELECT <dbid> where 
# dbid is a number between 0 and 'databases'-1 
databases 16 

################################ SNAPSHOTTING ################################# 
# 
# 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 at all commenting all the "save" lines. 

save 900 1 
save 300 10 
save 60 10000 

# Compress string objects using LZF when dump .rdb databases? 
# For default that's set to 'yes' as it's almost always a win. 
# If you want to save some CPU in the saving child set it to 'no' but 
# the dataset will likely be bigger if you have compressible values or keys. 
rdbcompression yes 

# The filename where to dump the DB 
dbfilename dump.rdb 

# The working directory. 
# 
# The DB will be written inside this directory, with the filename specified 
# above using the 'dbfilename' configuration directive. 
# 
# Also the Append Only File will be created inside this directory. 
# 
# Note that you must specify a directory here, not a file name. 
dir /backups/redisdumps 

################################# REPLICATION ################################# 

# Master-Slave replication. Use slaveof to make a Redis instance a copy of 
# another Redis server. Note that the configuration is local to the slave 
# so for example it is possible to configure the slave to save the DB with a 
# different interval, or to listen to another port, and so on. 
# 
# slaveof <masterip> <masterport> 

# If the master is password protected (using the "requirepass" configuration 
# directive below) it is possible to tell the slave to authenticate before 
# starting the replication synchronization process, otherwise the master will 
# refuse the slave request. 
# 
# masterauth <master-password> 

# When a slave lost the connection with the master, or when the replication 
# is still in progress, the slave can act in two different ways: 
# 
# 1) if slave-serve-stale-data is set to 'yes' (the default) the slave will 
# still reply to client requests, possibly with out of data data, or the 
# data set may just be empty if this is the first synchronization. 
# 
# 2) if slave-serve-stale data is set to 'no' the slave will reply with 
# an error "SYNC with master in progress" to all the kind of commands 
# but to INFO and SLAVEOF. 
# 
slave-serve-stale-data yes 

################################## SECURITY ################################### 

# Require clients to issue AUTH <PASSWORD> before processing any other 
# commands. This might be useful in environments in which you do not trust 
# others with access to the host running redis-server. 
# 
# This should stay commented out for backward compatibility and because most 
# people do not need auth (e.g. they run their own servers). 
# 
# Warning: since Redis is pretty fast an outside user can try up to 
# 150k passwords per second against a good box. This means that you should 
# use a very strong password otherwise it will be very easy to break. 
# 
# requirepass foobared 

# Command renaming. 
# 
# It is possilbe to change the name of dangerous commands in a shared 
# environment. For instance the CONFIG command may be renamed into something 
# of hard to guess so that it will be still available for internal-use 
# tools but not available for general clients. 
# 
# Example: 
# 
# rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52 
# 
# It is also possilbe to completely kill a command renaming it into 
# an empty string: 
# 
# rename-command CONFIG "" 

################################### LIMITS #################################### 

# Set the max number of connected clients at the same time. By default there 
# is no limit, and it's up to the number of file descriptors the Redis process 
# is able to open. The special value '0' means no limits. 
# Once the limit is reached Redis will close all the new connections sending 
# an error 'max number of clients reached'. 
# 
# maxclients 128 

# Don't use more memory than the specified amount of bytes. 
# When the memory limit is reached Redis will try to remove keys with an 
# EXPIRE set. It will try to start freeing keys that are going to expire 
# in little time and preserve keys with a longer time to live. 
# Redis will also try to remove objects from free lists if possible. 
# 
# If all this fails, Redis will start to reply with errors to commands 
# that will use more memory, like SET, LPUSH, and so on, and will continue 
# to reply to most read-only commands like GET. 
# 
# WARNING: maxmemory can be a good idea mainly if you want to use Redis as a 
# 'state' server or cache, not as a real DB. When Redis is used as a real 
# database the memory usage will grow over the weeks, it will be obvious if 
# it is going to use too much memory in the long run, and you'll have the time 
# to upgrade. With maxmemory after the limit is reached you'll start to get 
# errors for write operations, and this may even lead to DB inconsistency. 
# 
# maxmemory <bytes> 

# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory 
# is reached? You can select among five behavior: 
# 
# volatile-lru -> remove the key with an expire set using an LRU algorithm 
# allkeys-lru -> remove any key accordingly to the LRU algorithm 
# volatile-random -> remove a random key with an expire set 
# allkeys->random -> remove a random key, any key 
# volatile-ttl -> remove the key with the nearest expire time (minor TTL) 
# noeviction -> don't expire at all, just return an error on write operations 
# 
# Note: with all the kind of policies, Redis will return an error on write 
#  operations, when there are not suitable keys for eviction. 
# 
#  At the date of writing this commands are: set setnx setex append 
#  incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd 
#  sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby 
#  zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby 
#  getset mset msetnx exec sort 
# 
# The default is: 
# 
# maxmemory-policy volatile-lru 

# LRU and minimal TTL algorithms are not precise algorithms but approximated 
# algorithms (in order to save memory), so you can select as well the sample 
# size to check. For instance for default Redis will check three keys and 
# pick the one that was used less recently, you can change the sample size 
# using the following configuration directive. 
# 
# maxmemory-samples 3 

############################## APPEND ONLY MODE ############################### 

# By default Redis asynchronously dumps the dataset on disk. If you can live 
# with the idea that the latest records will be lost if something like a crash 
# happens this is the preferred way to run Redis. If instead you care a lot 
# about your data and don't want to that a single record can get lost you should 
# enable the append only mode: when this mode is enabled Redis will append 
# every write operation received in the file appendonly.aof. This file will 
# be read on startup in order to rebuild the full dataset in memory. 
# 
# Note that you can have both the async dumps and the append only file if you 
# like (you have to comment the "save" statements above to disable the dumps). 
# Still if append only mode is enabled Redis will load the data from the 
# log file at startup ignoring the dump.rdb file. 
# 
# IMPORTANT: Check the BGREWRITEAOF to check how to rewrite the append 
# log file in background when it gets too big. 

appendonly no 

# The name of the append only file (default: "appendonly.aof") 
# appendfilename appendonly.aof 

# The fsync() call tells the Operating System to actually write data on disk 
# instead to wait for more data in the output buffer. Some OS will really flush 
# data on disk, some other OS will just try to do it ASAP. 
# 
# Redis supports three different modes: 
# 
# no: don't fsync, just let the OS flush the data when it wants. Faster. 
# always: fsync after every write to the append only log . Slow, Safest. 
# everysec: fsync only if one second passed since the last fsync. Compromise. 
# 
# The default is "everysec" that's usually the right compromise between 
# speed and data safety. It's up to you to understand if you can relax this to 
# "no" that will will let the operating system flush the output buffer when 
# it wants, for better performances (but if you can live with the idea of 
# some data loss consider the default persistence mode that's snapshotting), 
# or on the contrary, use "always" that's very slow but a bit safer than 
# everysec. 
# 
# If unsure, use "everysec". 

# appendfsync always 
appendfsync everysec 
# appendfsync no 

# When the AOF fsync policy is set to always or everysec, and a background 
# saving process (a background save or AOF log background rewriting) is 
# performing a lot of I/O against the disk, in some Linux configurations 
# Redis may block too long on the fsync() call. Note that there is no fix for 
# this currently, as even performing fsync in a different thread will block 
# our synchronous write(2) call. 
# 
# In order to mitigate this problem it's possible to use the following option 
# that will prevent fsync() from being called in the main process while a 
# BGSAVE or BGREWRITEAOF is in progress. 
# 
# This means that while another child is saving the durability of Redis is 
# the same as "appendfsync none", that in pratical terms means that it is 
# possible to lost up to 30 seconds of log in the worst scenario (with the 
# default Linux settings). 
# 
# If you have latency problems turn this to "yes". Otherwise leave it as 
# "no" that is the safest pick from the point of view of durability. 
no-appendfsync-on-rewrite no 

################################## SLOW LOG ################################### 

# The Redis Slow Log is a system to log queries that exceeded a specified 
# execution time. The execution time does not include the I/O operations 
# like talking with the client, sending the reply and so forth, 
# but just the time needed to actually execute the command (this is the only 
# stage of command execution where the thread is blocked and can not serve 
# other requests in the meantime). 
# 
# You can configure the slow log with two parameters: one tells Redis 
# what is the execution time, in microseconds, to exceed in order for the 
# command to get logged, and the other parameter is the length of the 
# slow log. When a new command is logged the oldest one is removed from the 
# queue of logged commands. 

# The following time is expressed in microseconds, so 1000000 is equivalent 
# to one second. Note that a negative number disables the slow log, while 
# a value of zero forces the logging of every command. 
slowlog-log-slower-than 10000 

# There is no limit to this length. Just be aware that it will consume memory. 
# You can reclaim memory used by the slow log with SLOWLOG RESET. 
slowlog-max-len 1024 

################################ VIRTUAL MEMORY ############################### 

### WARNING! Virtual Memory is deprecated in Redis 2.4 
### The use of Virtual Memory is strongly discouraged. 

# Virtual Memory allows Redis to work with datasets bigger than the actual 
# amount of RAM needed to hold the whole dataset in memory. 
# In order to do so very used keys are taken in memory while the other keys 
# are swapped into a swap file, similarly to what operating systems do 
# with memory pages. 
# 
# To enable VM just set 'vm-enabled' to yes, and set the following three 
# VM parameters accordingly to your needs. 

vm-enabled no 
# vm-enabled yes 

# This is the path of the Redis swap file. As you can guess, swap files 
# can't be shared by different Redis instances, so make sure to use a swap 
# file for every redis process you are running. Redis will complain if the 
# swap file is already in use. 
# 
# The best kind of storage for the Redis swap file (that's accessed at random) 
# is a Solid State Disk (SSD). 
# 
# *** WARNING *** if you are using a shared hosting the default of putting 
# the swap file under /tmp is not secure. Create a dir with access granted 
# only to Redis user and configure Redis to create the swap file there. 
vm-swap-file /tmp/redis.swap 

# vm-max-memory configures the VM to use at max the specified amount of 
# RAM. Everything that deos not fit will be swapped on disk *if* possible, that 
# is, if there is still enough contiguous space in the swap file. 
# 
# With vm-max-memory 0 the system will swap everything it can. Not a good 
# default, just specify the max amount of RAM you can in bytes, but it's 
# better to leave some margin. For instance specify an amount of RAM 
# that's more or less between 60 and 80% of your free RAM. 
vm-max-memory 0 

# Redis swap files is split into pages. An object can be saved using multiple 
# contiguous pages, but pages can't be shared between different objects. 
# So if your page is too big, small objects swapped out on disk will waste 
# a lot of space. If you page is too small, there is less space in the swap 
# file (assuming you configured the same number of total swap file pages). 
# 
# If you use a lot of small objects, use a page size of 64 or 32 bytes. 
# If you use a lot of big objects, use a bigger page size. 
# If unsure, use the default :) 
vm-page-size 32 

# Number of total memory pages in the swap file. 
# Given that the page table (a bitmap of free/used pages) is taken in memory, 
# every 8 pages on disk will consume 1 byte of RAM. 
# 
# The total swap size is vm-page-size * vm-pages 
# 
# With the default of 32-bytes memory pages and 134217728 pages Redis will 
# use a 4 GB swap file, that will use 16 MB of RAM for the page table. 
# 
# It's better to use the smallest acceptable value for your application, 
# but the default is large in order to work in most conditions. 
vm-pages 134217728 

# Max number of VM I/O threads running at the same time. 
# This threads are used to read/write data from/to swap file, since they 
# also encode and decode objects from disk to memory or the reverse, a bigger 
# number of threads can help with big objects even if they can't help with 
# I/O itself as the physical device may not be able to couple with many 
# reads/writes operations at the same time. 
# 
# The special value of 0 turn off threaded I/O and enables the blocking 
# Virtual Memory implementation. 
vm-max-threads 4 

############################### ADVANCED CONFIG ############################### 

# Hashes are encoded in a special way (much more memory efficient) when they 
# have at max a given numer of elements, and the biggest element does not 
# exceed a given threshold. You can configure this limits with the following 
# configuration directives. 
hash-max-zipmap-entries 512 
hash-max-zipmap-value 64 

# Similarly to hashes, small lists are also encoded in a special way in order 
# to save a lot of space. The special representation is only used when 
# you are under the following limits: 
list-max-ziplist-entries 512 
list-max-ziplist-value 64 

# Sets have a special encoding in just one case: when a set is composed 
# of just strings that happens to be integers in radix 10 in the range 
# of 64 bit signed integers. 
# The following configuration setting sets the limit in the size of the 
# set in order to use this special memory saving encoding. 
set-max-intset-entries 512 

# Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in 
# order to help rehashing the main Redis hash table (the one mapping top-level 
# keys to values). The hash table implementation redis uses (see dict.c) 
# performs a lazy rehashing: the more operation you run into an hash table 
# that is rhashing, the more rehashing "steps" are performed, so if the 
# server is idle the rehashing is never complete and some more memory is used 
# by the hash table. 
# 
# The default is to use this millisecond 10 times every second in order to 
# active rehashing the main dictionaries, freeing memory when possible. 
# 
# If unsure: 
# use "activerehashing no" if you have hard latency requirements and it is 
# not a good thing in your environment that Redis can reply form time to time 
# to queries with 2 milliseconds delay. 
# 
# use "activerehashing yes" if you don't have such hard requirements but 
# want to free memory asap when possible. 
activerehashing yes 

################################## INCLUDES ################################### 

# Include one or more other config files here. This is useful if you 
# have a standard template that goes to all redis server but also need 
# to customize a few per-server settings. Include files can include 
# other files, so use this wisely. 
# 
# include /path/to/local.conf 
# include /path/to/other.conf 

Answer 1

Wydaje się, że znalazłem rozwiązanie tutaj: http://redis4you.com/articles.php?id=012&name=redis

Na linux należy zmienić ustawienia jądra, aby zoptymalizować operacje TCP dla wysokiego obciążenia:

echo 1 > /proc/sys/net/ipv4/tcp_tw_reuse 
echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle 

Co więcej, po ponownym uruchomieniu ustaw te zmiany na stałe, dodając odłogowanie do /etc/sysctl.conf:

net.ipv4.tcp_tw_reuse = 1 
net.ipv4.tcp_tw_recycle = 1 

Dodatkowo, pomogło ustawienie timeout do 0 w redis.conf:

# Close the connection after a client is idle for N seconds (0 to disable) 
timeout 0 

Answer 2

Znaleźliśmy jeśli używasz AOF wytrwałości wraz z migawkami RDB, czasem uaktualnianie rdb może opóźnić AOF aktualizowany, co w włącz powoduje, że zapisuje do redis do zablokowania. Wyłączenie opieki wyleczyło okresowe opóźnienie, które mieliśmy, co było dla nas dobre, ponieważ utrata ostatnich kilku kluczy z powodu awarii nie była ważna.