Project: ClickHouse (App Definition and Development / Database)
File: tips.md

slug: /en/operations/tips sidebar_position: 58 sidebar_label: Usage Recommendations title: "Usage Recommendations" import SelfManaged from '@site/docs/en/snippets/selfmanagedonly_automated.md'; <SelfManaged /> Always use the `performance` scaling governor. The `on-demand` scaling governor works much worse with constantly high demand. ``` bash $ echo 'performance' | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor ``` Processors can overheat. Use `dmesg` to see if the CPUs clock rate was limited due to overheating. The restriction can also be set externally at the datacenter level. You can use `turbostat` to monitor it under a load. For small amounts of data (up to ~200 GB compressed), it is best to use as much memory as the volume of data. For large amounts of data and when processing interactive (online) queries, you should use a reasonable amount of RAM (128 GB or more) so the hot data subset will fit in the cache of pages. Even for data volumes of ~50 TB per server, using 128 GB of RAM significantly improves query performance compared to 64 GB. Do not disable overcommit. The value `cat /proc/sys/vm/overcommit_memory` should be 0 or 1. Run ``` bash $ echo 0 | sudo tee /proc/sys/vm/overcommit_memory ``` Use `perf top` to watch the time spent in the kernel for memory management. Permanent huge pages also do not need to be allocated. :::warning If your system has less than 16 GB of RAM, you may experience various memory exceptions because default settings do not match this amount of memory. The recommended amount of RAM is 32 GB or more. You can use ClickHouse in a system with a small amount of RAM, even with 2 GB of RAM, but it requires additional tuning and can ingest at a low rate. ::: If your budget allows you to use SSD, use SSD. If not, use HDD. SATA HDDs 7200 RPM will do. Give preference to a lot of servers with local hard drives over a smaller number of servers with attached disk shelves. But for storing archives with rare queries, shelves will work. When using HDD, you can combine their RAID-10, RAID-5, RAID-6 or RAID-50. For Linux, software RAID is better (with `mdadm`). When creating RAID-10, select the `far` layout. If your budget allows, choose RAID-10. LVM by itself (without RAID or `mdadm`) is ok, but making RAID with it or combining it with `mdadm` is a less explored option, and there will be more chances for mistakes (selecting wrong chunk size; misalignment of chunks; choosing a wrong raid type; forgetting to cleanup disks). If you are confident in using LVM, there is nothing against using it. If you have more than 4 disks, use RAID-6 (preferred) or RAID-50, instead of RAID-5. When using RAID-5, RAID-6 or RAID-50, always increase stripecachesize, since the default value is usually not the best

``` bash $ echo 4096 | sudo tee /sys/block/md2/md/stripecachesize ``` Calculate the exact number from the number of devices and the block size, using the formula: `2 num_devices chunksizein_bytes / 4096`. A block size of 64 KB is sufficient for most RAID configurations. The average clickhouse-server write size is approximately 1 MB (1024 KB), and thus the recommended stripe size is also 1 MB. The block size can be optimized if needed when set to 1 MB divided by the number of non-parity disks in the RAID array, such that each write is parallelized across all available non-parity disks. Never set the block size too small or too large. You can use RAID-0 on SSD. Regardless of RAID use, always use replication for data security. Enable NCQ with a long queue. For HDD, choose the mq-deadline or CFQ scheduler, and for SSD, choose noop. Dont reduce the readahead setting. For HDD, enable the write cache. Make sure that ) is enabled for NVME and SSD disks in your OS (usually it's implemented using a cronjob or systemd service). Ext4 is the most reliable option. Set the mount options `noatime`. XFS works well too. Most other file systems should also work fine. FAT-32 and exFAT are not supported due to lack of hard links. Do not use compressed filesystems, because ClickHouse does compression on its own and better. It's not recommended to use encrypted filesystems, because you can use builtin encryption in ClickHouse, which is better. While ClickHouse can work over NFS, it is not the best idea. Don't use an outdated Linux kernel. If you are using IPv6, increase the size of the route cache. The Linux kernel prior to 3.2 had a multitude of problems with IPv6 implementation. Use at least a 10 GB network, if possible. 1 Gb will also work, but it will be much worse for patching replicas with tens of terabytes of data, or for processing distributed queries with a large amount of intermediate data. If you are using old Linux kernel, disable transparent huge pages. It interferes with memory allocator, which leads to significant performance degradation. On newer Linux kernels transparent huge pages are alright. ``` bash $ echo 'madvise' | sudo tee /sys/kernel/mm/transparent_hugepage/enabled ``` If you want to modify the transparent huge pages setting permanently, editing the `/etc/default/grub` to add the `transparenthugepage=madvise` to the `GRUBCMDLINELINUXDEFAULT` option: ```bash $ GRUBCMDLINELINUXDEFAULT="transparenthugepage=madvise ..." ``` After that, run the `sudo update-grub` command then reboot to take effect. If you are using OpenStack, set ``` cpu_mode=host-passthrough ``` in `nova.conf`. If you are using libvirt, set ``` <cpu mode='host-passthrough'/> ``` in XML configuration. This is important for ClickHouse to be able to get correct information with `cpuid` instruction. Otherwise you may get `Illegal instruction` crashes when hypervisor is run on old CPU models. ClickHouse Keeper is recommended to replace ZooKeeper for ClickHouse

See the documentation for If you would like to continue using ZooKeeper then it is best to use a fresh version of ZooKeeper 3.4.9 or later. The version in stable Linux distributions may be outdated. You should never use manually written scripts to transfer data between different ZooKeeper clusters, because the result will be incorrect for sequential nodes. Never use the zkcopy utility for the same reason: https://github.com/ksprojects/zkcopy/issues/15 If you want to divide an existing ZooKeeper cluster into two, the correct way is to increase the number of its replicas and then reconfigure it as two independent clusters. You can run ClickHouse Keeper on the same server as ClickHouse in test environments, or in environments with low ingestion rate. For production environments we suggest to use separate servers for ClickHouse and ZooKeeper/Keeper, or place ClickHouse files and Keeper files on to separate disks. Because ZooKeeper/Keeper are very sensitive for disk latency and ClickHouse may utilize all available system resources. You can have ZooKeeper observers in an ensemble but ClickHouse servers should not interact with observers. Do not change `minSessionTimeout` setting, large values may affect ClickHouse restart stability. With the default settings, ZooKeeper is a time bomb: The ZooKeeper server wont delete files from old snapshots and logs when using the default configuration (see `autopurge`), and this is the responsibility of the operator. This bomb must be defused. The ZooKeeper (3.5.1) configuration below is used in a large production environment: zoo.cfg: ``` bash tickTime=2000 initLimit=300 syncLimit=10 maxClientCnxns=2000 maxSessionTimeout=60000000 dataDir=/opt/zookeeper/{{ '{{' }} cluster['name'] {{ '}}' }}/data dataLogDir=/opt/zookeeper/{{ '{{' }} cluster['name'] {{ '}}' }}/logs autopurge.snapRetainCount=10 autopurge.purgeInterval=1 preAllocSize=131072 snapCount=3000000 leaderServes=yes standaloneEnabled=false dynamicConfigFile=/etc/zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }}/conf/zoo.cfg.dynamic ``` Java version: ``` text openjdk 11.0.5-shenandoah 2019-10-15 OpenJDK Runtime Environment (build 11.0.5-shenandoah+10-adhoc.heretic.src) OpenJDK 64-Bit Server VM (build 11.0.5-shenandoah+10-adhoc.heretic.src, mixed mode) ``` JVM parameters: ``` bash NAME=zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }} ZOOCFGDIR=/etc/$NAME/conf CLASSPATH="$ZOOCFGDIR:/usr/build/classes:/usr/build/lib/*.jar:/usr/share/zookeeper-3.6.2/lib/audience-annotations-0.5.0.jar:/usr/share/zookeeper-3.6.2/lib/commons-cli-1.2.jar:/usr/share/zookeeper-3.6.2/lib/commons-lang-2.6.jar:/usr/share/zookeeper-3.6.2/lib/jackson-annotations-2.10.3.jar:/usr/share/zookeeper-3.6.2/lib/jackson-core-2.10.3.jar:/usr/share/zookeeper-3.6.2/lib/jackson-databind-2.10.3.jar:/usr/share/zookeeper-3.6.2/lib/javax.servlet-api-3.1.0.jar:/usr/share/zookeeper-3.6.2/lib/jetty-http-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jetty-io-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jetty-security-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jetty-server-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jetty-servlet-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jetty-util-9.4.24.v20191120.jar:/usr/share/zookeeper-3.6.2/lib/jline-2.14.6.jar:/usr/share/zookeeper-3.6.2/lib/json-simple-1.1.1.jar:/usr/share/zookeeper-3.6.2/lib/log4j-1.2.17.jar:/usr/share/zookeeper-3.6.2/lib/metrics-core-3.2.5.jar:/usr/share/zookeeper-3.6.2/lib/netty-buffer-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-codec-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-common-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-handler-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-resolver-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-transport-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-transport-native-epoll-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/netty-transport-native-unix-common-4.1.50.Final.jar:/usr/share/zookeeper-3.6.2/lib/simpleclient-0.6.0.jar:/usr/share/zookeeper-3.6.2/lib/simpleclientcommon-0.6.0.jar:/usr/share/zookeeper-3.6.2/lib/simpleclienthotspot-0.6.0.jar:/usr/share/zookeeper-3.6.2/lib/simpleclient_servlet-0.6.0.jar:/usr/share/zookeeper-3.6.2/lib/slf4j-api-1.7.25.jar:/usr/share/zookeeper-3.6.2/lib/slf4j-log4j12-1.7.25.jar:/usr/share/zookeeper-3.6.2/lib/snappy-java-1.1.7.jar:/usr/share/zookeeper-3.6.2/lib/zookeeper-3.6.2.jar:/usr/share/zookeeper-3.6.2/lib/zookeeper-jute-3.6.2.jar:/usr/share/zookeeper-3.6.2/lib/zookeeper-prometheus-metrics-3.6.2.jar:/usr/share/zookeeper-3.6.2/etc" ZOOCFG="$ZOOCFGDIR/zoo.cfg" ZOOLOGDIR=/var/log/$NAME USER=zookeeper GROUP=zookeeper PIDDIR=/var/run/$NAME PIDFILE=$PIDDIR/$NAME.pid SCRIPTNAME=/etc/init.d/$NAME JAVA=/usr/local/jdk-11/bin/java ZOOMAIN="org.apache.zookeeper.server.quorum.QuorumPeerMain" ZOOLOG4JPROP="INFO,ROLLINGFILE" JMXLOCALONLY=false JAVA_OPTS="-Xms{{ '{{' }} cluster.get('xms','128M') {{ '}}' }} \ -Xmx{{ '{{' }} cluster.get('xmx','1G') {{ '}}' }} \ -Xlog:safepoint,gc=info,age=debug:file=/var/log/$NAME/zookeeper-gc.log:time,level,tags:filecount=16,filesize=16M -verbose:gc \ -XX:+UseG1GC \ -Djute.maxbuffer=8388608 \ -XX:MaxGCPauseMillis=50" ``` Salt initialization: ``` text description "zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }} centralized coordination service" start on runlevel [2345] stop on runlevel [!2345] respawn limit nofile 8192 8192 pre-start script [ -r "/etc/zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }}/conf/environment" ] || exit 0 . /etc/zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }}/conf/environment [ -d $ZOOLOGDIR ] || mkdir -p $ZOOLOGDIR chown $USER:$GROUP $ZOOLOGDIR end script script . /etc/zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }}/conf/environment [ -r /etc/default/zookeeper ] && . /etc/default/zookeeper if [ -z "$JMXDISABLE" ]; then JAVAOPTS="$JAVAOPTS -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=$JMXLOCALONLY" fi exec start-stop-daemon --start -c $USER --exec $JAVA --name zookeeper-{{ '{{' }} cluster['name'] {{ '}}' }} \ -- -cp $CLASSPATH $JAVAOPTS -Dzookeeper.log.dir=${ZOOLOG_DIR} \ -Dzookeeper.root.logger=${ZOOLOG4JPROP} $ZOOMAIN $ZOOCFG end script ``` If you use antivirus software configure it to skip folders with ClickHouse datafiles (`/var/lib/clickhouse`) otherwise performance may be reduced and you may experience unexpected errors during data ingestion and background merges.