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https://github.com/assafmo/couchdb-linux-performance

Linux tuning for CouchDB performance
https://github.com/assafmo/couchdb-linux-performance

couchdb couchdb-performance linux-tuning

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Linux tuning for CouchDB performance

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# Linux tuning for better CouchDB performance



## Filesystem tuning



### ext4



#### Mount options (or via /etc/fstab)



`errors=remount-ro,noatime,nouser_xattr,barrier=0`



#### Journal



(Replace `sdXY` with your partition name)



##### Check if exists



`sudo tune2fs -l /dev/sdXY | fgrep has_journal`



##### Turn Off/On



Unmount filesystem (If root filesystem then mount read-only) and then:  

`tune2fs -O ^has_journal /dev/sdXY`



### xfs



#### Mount options (or via /etc/fstab)



`noatime,nodiratime,logbufs=8,logbsize=256k,nobarrier`



## /etc/rc.local



(Replace `sdX` with your device name)



```bash

####

## IO Scheduler

####



# First, set an appropriate IO scheduler for file servers.

# deadline - For spinning disks

# noop     - For VMs and SSDs

echo noop > /sys/block/sdX/queue/scheduler



# Now give the IO scheduler more flexibility by increasing the number of schedulable requests:

echo 4096 > /sys/block/sdX/queue/nr_requests



# To improve throughput for sequential reads, increase the maximum amount of read-ahead data.

# The actual amount of read-ahead is adaptive,

# so using a high value here won't harm performance for small random access.

echo 4096 > /sys/block/sdX/queue/read_ahead_kb



####

## Virtual memory settings

####



# To avoid long IO stalls (latencies) for write cache flushing

# in a production environment with very different workloads,

# you will typically want to limit the kernel dirty (write) cache size:

echo 5 > /proc/sys/vm/dirty_background_ratio

echo 10 > /proc/sys/vm/dirty_ratio



# Assigning slightly higher priority to inode caching helps

# to avoid disk seeks for inode loading:

echo 50 > /proc/sys/vm/vfs_cache_pressure



# Decrease swappiness to prevent swapping as much as possible

echo 1 > /proc/sys/vm/swappiness



# Buffering of file system data requires frequent memory allocation.

# Raising the amount of reserved kernel memory will enable faster and more reliable

# memory allocation in critical situations.

# Raise the corresponding value to 64MB if you have less than 8GB of memory,

# otherwise raise it to at least 256MB:

echo 262144 > /proc/sys/vm/min_free_kbytes



# It is recommended to have transparent huge pages disabled:

echo madvise > /sys/kernel/mm/transparent_hugepage/enabled



####

## Process scheduler

####



# There's a kernel parameter that determines how long a migrated process has to be running

# before the kernel will consider migrating it again to another core.

# The sysctl name is sched_migration_cost_ns, default value 50000 (that's ns so 0.5 ms).

# Forking servers, like PostgreSQL or Apache, scale to much higher levels of concurrent

# connections if this is made larger, by at least an order of magnitude:

echo 5000000 > /proc/sys/kernel/sched_migration_cost_ns



# Another parameter that can dramatically impact forking servers is sched_autogroup_enabled.

# This setting groups tasks by TTY, to improve perceived responsiveness on an interactive system.

# On a server with a long running forking daemon, this will tend to keep child processes from

# migrating away as soon as they should.

# It can be disabled like so:

echo 0 > /proc/sys/kernel/sched_autogroup_enabled



####

## CPU

####



# Set the scaling governor to performance. This keeps the CPU at maximum frequency

echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

```



### Apply the changes



`sudo /etc/rc.local` or `reboot`



## ionice



:warning: Using `ionice` is effective if and only if IO scheduler uses an algorithm that takes

priorities into account. If you have followed this guide so far, using `ionice` will have no effect

since you have set IO Scheduler to `deadline` or `noop` which doesn't use priorities.

Look for `cfq` for a scheduler that works with priorities.



Giving CouchDB IO priority with `ionice`: `sudo ionice -p $(pidof beam.smp) -c 1 -n 0`.  

This can also be done in a [`systemd` unit](https://gist.github.com/SinanGabel/eac83a2f9d0ac64e2c9d4bd936be9313/3d302ee7b2667b70c8372e4f6ce4891811f2fb94#file-couchdb-2-0-install-L116):



```

IOSchedulingClass=1

IOSchedulingPriority=0

```



## Sources:



- https://www.beegfs.com/wiki/StorageServerTuning

- https://tweaked.io/guide/kernel/

- https://developer.couchbase.com/documentation/server/current/install/install-swap-space.html

- http://www.tutorialspoint.com/unix_commands/ionice.htm

- https://www.freedesktop.org/software/systemd/man/systemd.exec.html

- https://blog.nelhage.com/post/transparent-hugepages/

- https://www.kernel.org/doc/Documentation/cpu-freq/governors.txt

- https://blog.codeship.com/linux-io-scheduler-tuning/

- https://askubuntu.com/a/784504