Adapting Memory Settings

1 Minimal Requirements

The system should provide at least 4GB of memory and it is mandatory to use a 64Bit Kernel/System.

Overview over memory distribution for the basic Gentics CMS package.

Programm	Memory Usage
MySQL	500 MB
JVM + JCS-Cache	1024 MB
Total	1524 MB

1.1 JVM Garbage Collector Settings

When using JDK 8, we advise to enable the concurrent mark sweep garbage collector to avoid long duration full garbage collections.


-XX:+UseConcMarkSweepGC

See Virtual Machine Garbage Collection Tuning for more information.

When using JDK 11, we advise to use the default G1 garbage collector.

2 JCS Cache Size

The node object cache is a Java cache inside of the CMS. This cache is used to cache node objects like pages, templates and files. Increasing this memory can help speed up the loading times of pages in preview mode and the publishing process.

conf/cache.ccf


  jcs.region.gentics-nodeobjects.cacheattributes.MaxObjects=100000

By default the largest cache region is configured to hold 100k objects. An object size of 1kB is assumed for this cache setting. The memory requirements depend upon the existing content. The profiler webapp can be used to create a differential measurement (Full GC, Check Used Memory, Cache Clear). An OutOfMemoryException or stalling garbage collection can occur when the cache region is too large for the heap memory.

2.1 Rule of thumb

Assume 50 kB to 300 kB per object and apply the following formula:

Cache memory usage = 50 kB * object count (Page, Folder, Image, File…) to 300 kB * object count (Page, Folder, Image, File…).

2.2 Individual caches for object types

It is possible to configure individual caches for specific object types. This can be useful to enforce caching of some objects (e.g. folders) for performance reasons. Since folders are frequently used (to display the folder tree and also for checking object permissions), it is recommended to configure a separate cache for folders and make it big enough so that it can hold all existing folders.

conf/*.yml


node_cache:
  "10002": "gentics-nodeobjects-folders"

conf/cache.ccf


jcs.region.gentics-nodeobjects-folders=
jcs.region.gentics-nodeobjects-folders.cacheattributes.MaxObjects=50000
jcs.region.gentics-nodeobjects-folders.elementattributes.MaxLifeSeconds=86400
jcs.region.gentics-nodeobjects-folders.elementattributes.MaxMemoryIdleTimeSeconds=86400

3 Connection Pool

The default max_connections limits for MySQL 5.5/5.6 is 151. We suggest to use 80% of the server connection limit for the Gentics CMS connection pool.

Generally it is a good idea to increase this limit to a value of > 250. This is especially important for production systems with multiple concurrent users.

You can check the connection limit by logging in your MySQL server and execute the following command:


  show variables like 'max_connections';

The pool_whenExhaustedAction setting can have the following values:

BLOCK: The connection pool will no longer hand out connections when the limit was reached (Suggested action)
GROW: The connection pool will continue growing even if the limit has been reached. (Current default action)
FAIL: The connection pool will throw exceptions when the limit was reached.

con/*.yml


db:
  settings:
    # pool_size_max = 0.8 * max_connections (151)
    pool_size_max: 120
    pool_whenExhaustedAction: "BLOCK"
    # set the maximum wait time to 30 seconds
    pool_maxWait: 30000

If the pool_whenExhaustedAction is set to BLOCK, it is important to also set a positive pool_maxWait timeout in order to avoid deadlocks in the CMS.

4 MySQL Memory

The main MySQL settings are innodb_buffer_pool_size and innodb_log_file_size.

gentics_custom.cnf


  // This option will change the way the mysql synchonizes the written data
  // with the disk. Value 2 means that the sync action for the mysql data
  // logfile is invoked once per second.
  innodb_flush_log_at_trx_commit=2
  // Should be 50-80% of main mysql memory
  innodb_buffer_pool_size=2048M
  // Should be 25% of innodb_buffer_pool_size
  innodb_log_file_size=512M
  // Be careful not to set the size of the cache too large. Due to the need
  // for threads to lock the cache during updates, you may see lock contention
  // issues with a very large cache.
  query_cache_size=64M

Please note that changes to innodb_log_file_size require the deletion of the MySQL logfile and a restart of the MySQL server.

5 Example Configuration

Please note that the following values should only be considered as a guideline for planned memory setups.

5.1 8 GB


  # /cms/conf/cache.ccf - 380k (10k per object)
  jcs.region.gentics-nodeobjects.cacheattributes.MaxObjects=280000

  export JAVA_OPTS="-Dcom.gentics.contentnode.config.files=cms -Xmx3686m -Xms3686m -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+UseConcMarkSweepGC -XX:+HeapDumpOnOutOfMemoryError -Djava.awt.headless=true"

  # gentics_custom.cnf
  innodb_flush_log_at_trx_commit=2
  innodb_buffer_pool_size=3276M
  innodb_log_file_size=819M
  query_cache_size=64M
  max_connections=200

  # gtx_gcn_custom.ini
  apc.shm_size=128M

5.2 16 GB


  # /cms/conf/cache.ccf - 780k (10kb per object)
  jcs.region.gentics-nodeobjects.cacheattributes.MaxObjects=590000

  export JAVA_OPTS="-Dcom.gentics.contentnode.config.files=cms -Xmx7680m -Xms7680m -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+UseConcMarkSweepGC -XX:+HeapDumpOnOutOfMemoryError -Djava.awt.headless=true"

  # gentics_custom.cnf
  innodb_flush_log_at_trx_commit=2
  innodb_buffer_pool_size=6656M
  innodb_log_file_size=1664M
  query_cache_size=128M
  max_connections=250

  # gtx_gcn_custom.ini
  apc.shm_size=256M

5.3 32 GB


  # /cms/conf/cache.ccf - 1.5 million (10kb per object)
  jcs.region.gentics-nodeobjects.cacheattributes.MaxObjects=1100000

  export JAVA_OPTS="-Dcom.gentics.contentnode.config.files=cms -Xmx14336m -Xms14336m -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+UseConcMarkSweepGC -XX:+HeapDumpOnOutOfMemoryError -Djava.awt.headless=true"

  # gentics_custom.cnf
  innodb_flush_log_at_trx_commit=2
  innodb_buffer_pool_size=13312M
  innodb_log_file_size=3328M
  query_cache_size=128M
  max_connections=300

  # gtx_gcn_custom.ini
  apc.shm_size=512M

6 Memory Formula

Memory Value	Formula/Value
Average Object Size (Pages, Files, Folders, Images..)	10 kB
MySQL Memory	Total Memory * 0.4
Java Heap Memory	Total Memory * 0.45
JCS Node Object Cache Count	(JavaMemory * 0.75) / Average Object Size
System Memory	0.5 GB

Gentics CMS Documentation