Tuning Large Scale Deployments

Description

The maximum number of HTTP requests served simultaneously by Apache httpd. Proxies, Web UI, and XMLRPC API clients each consume one. Requests exceeding the parameter will be queued and might result in timeouts.

Tune when

User count and proxy count increase significantly and this line appears in /var/log/apache2/error_log: […​] [mpm_prefork:error] [pid …​] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting.

Value default

150

Value recommendation

150-500

Location

/etc/apache2/server-tuning.conf, in the prefork.c section

Example

MaxClients = 200

After changing

Immediately change ServerLimit and check maxThreads for possible adjustment.

Notes

This parameter was renamed to MaxRequestWorkers, both names are valid.

More information

https://httpd.apache.org/docs/2.4/en/mod/mpm_common.html#maxrequestworkers

Description

The number of Apache httpd processes serving HTTP requests simultaneously. The number must equal MaxClients.

Tune when

MaxClients changes

Value default

150

Value recommendation

The same value as MaxClients

Location

/etc/apache2/server-tuning.conf, in the prefork.c section

Example

ServerLimit = 200

More information

https://httpd.apache.org/docs/2.4/en/mod/mpm_common.html#serverlimit

Description

The number of Tomcat threads dedicated to serving HTTP requests

Tune when

MaxClients changes. maxThreads must always be equal or greater than MaxClients

Value default

150

Value recommendation

The same value as MaxClients

Location

/etc/tomcat/server.xml

Example

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" URIEncoding="UTF-8" address="127.0.0.1" maxThreads="200" connectionTimeout="20000"/>

More information

https://tomcat.apache.org/tomcat-9.0-doc/config/http.html

Description

The number of milliseconds before a non-responding AJP connection is forcibly closed.

Tune when

Client count increases significantly and AH00992, AH00877, and AH01030 errors appear in Apache error logs during a load peak.

Value default

900000

Value recommendation

20000-3600000

Location

/etc/tomcat/server.xml

Example

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" URIEncoding="UTF-8" address="127.0.0.1" maxThreads="200" connectionTimeout="1000000" keepAliveTimeout="300000"/>

More information

https://tomcat.apache.org/tomcat-9.0-doc/config/http.html

Description

The number of milliseconds without data exchange from the JVM before a non-responding AJP connection is forcibly closed.

Tune when

Client count increases significantly and AH00992, AH00877, and AH01030 errors appear in Apache error logs during a load peak.

Value default

300000

Value recommendation

20000-600000

Location

/etc/tomcat/server.xml

Example

<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" URIEncoding="UTF-8" address="127.0.0.1" maxThreads="200" connectionTimeout="1000000" keepAliveTimeout="400000"/>

More information

https://tomcat.apache.org/tomcat-9.0-doc/config/http.html

Description

The maximum amount of memory Tomcat can use

Tune when

java.message_queue_thread_pool_size is increased or OutOfMemoryException errors appear in /var/log/rhn/rhn_web_ui.log

Value default

1 GiB

Value recommendation

4-8 GiB

Location

/etc/tomcat/conf.d/tomcat_java_opts.conf

Example

JAVA_OPTS="…​ -Xmx8G …​"

After changing

Check memory usage

More information

https://docs.oracle.com/javase/8/docs/technotes/tools/windows/java.html

Description

Disable displaying the update status for clients of a system group

Tune when

displaying the update status causes timeouts

Value default

false

Value recommendation

Location

/etc/rhn/rhn.conf

Example

java.disable_list_update_status = true

After changing

?

Notes

More information

man rhn.conf

Description

The maximum number of threads in Tomcat dedicated to asynchronous operations

Tune when

Client count increases significantly

Value default

5

Value recommendation

50 - 150

Location

/etc/rhn/rhn.conf

Example

java.message_queue_thread_pool_size = 50

After changing

Check hibernate.c3p0.max_size, as each thread consumes a PostgreSQL connection, starvation might happen if the allocated connection pool is insufficient. Check thread_pool, as each thread might perform Salt API calls, starvation might happen if the allocated Salt thread pool is insufficient. Check Tomcat’s -Xmx, as each thread consumes memory, OutOfMemoryException might be raised if insufficient.

Notes

Incoming Salt events are handled in separate thread pool, see java.salt_event_thread_pool_size

More information

man rhn.conf

Description

The maximum number of minions concurrently executing a scheduled action.

Tune when

Client count reaches several thousands and actions are not executed quickly enough.

Value default

200

Value recommendation

200-500

Location

/etc/rhn/rhn.conf

Example

java.salt_batch_size = 300

After changing

Check memory usage. Monitor memory usage closely before and after the change.

More information

Salt Rate Limiting

Description

The maximum number of threads in Tomcat dedicated to handling of incoming Salt events.

Tune when

The number of queued Salt events grows. Typically, this can happen during onboarding of large number of minions with higher value of java.salt_presence_ping_timeout. The number of events can be queried by echo "select count(*) from susesaltevent;" | spacewalk-sql --select-mode-direct -

Value default

8

Value recommendation

20-100

Location

/etc/rhn/rhn.conf

Example

java.salt_event_thread_pool_size = 50

After changing

Check the length of Salt event queue. Check hibernate.c3p0.max_size, as each thread consumes a PostgreSQL connection, starvation might happen if the allocated connection pool is insufficient. Check thread_pool, as each thread might perform Salt API calls, starvation might happen if the allocated Salt thread pool is insufficient. Check Tomcat’s -Xmx, as each thread consumes memory, OutOfMemoryException might be raised if insufficient.

More information

man rhn.conf

Description

Before any action is executed on a client, a presence ping is executed to make sure the client is reachable. This parameter sets the amount of time before a second command (in most cases state.apply or any other Salt function) is sent to the client to verify its presence. Having many clients typically means some will respond faster than others, so this timeout could be raised to accommodate for the slower ones.

Tune when

Client count increases significantly, or some clients are responding correctly but too slowly, and Uyuni excludes them from calls. This line appears in /var/log/rhn/rhn_web_ui.log: "Got no result for <COMMAND> on minion <MINION_ID> (minion did not respond in time)"

Value default

4 seconds

Value recommendation

4-20 seconds

Location

/etc/rhn/rhn.conf

Example

java.salt_presence_ping_timeout = 10

After changing

Large java.salt_presence_ping_timeout value can reduce overall throughput. This can be compensated by increasing java.salt_event_thread_pool_size

More information

Salt Timeouts

Description

Before any action is executed on a client, a presence ping is executed to make sure the client is reachable. After java.salt_presence_ping_timeout seconds have elapsed without a response, a second command (in most cases state.apply or any other Salt function) is sent to the client and if there is no response from the client for the amount of seconds specified with this parameter one more call (saltutil.find_job) is sent for a final check. This parameter sets the number of seconds after the second command after which the client is definitely considered timeout. Having many clients typically means some will respond faster than others, so this timeout could be raised to accommodate for the slower ones.

Tune when

Client count increases significantly, or some clients are responding correctly but too slowly, and Uyuni excludes them from calls. This line appears in /var/log/rhn/rhn_web_ui.log: "Got no result for <COMMAND> on minion <MINION_ID> (minion did not respond in time)"

Value default

1 second

Value recommendation

1-50 seconds

Location

/etc/rhn/rhn.conf

Example

java.salt_presence_ping_gather_job_timeout = 20

More information

Salt Timeouts

Description

Whenever content is changed in a software channel, its metadata needs to be recomputed before clients can use it. Channel-altering operations include the addition of a patch, the removal of a package or a repository synchronization run. This parameter specifies the maximum number of Taskomatic threads that Uyuni will use to recompute the channel metadata. Channel metadata computation is both CPU-bound and memory-heavy, so raising this parameter and operating on many channels simultaneously could cause Taskomatic to consume significant resources, but channels will be available to clients sooner.

Tune when

Channel count increases significantly (more than 50), or more concurrent operations on channels are expected.

Value default

2

Value recommendation

2-10

Location

/etc/rhn/rhn.conf

Example

java.taskomatic_channel_repodata_workers = 4

After changing

Check taskomatic.java.maxmemory for adjustment, as every new thread will consume memory

More information

man rhn.conf

Description

The maximum amount of memory Taskomatic can use. Generation of metadata, especially for some OSs, can be memory-intensive, so this parameter might need raising depending on the managed OS mix.

Tune when

java.taskomatic_channel_repodata_workers increases, OSs are added to Uyuni (particularly Red Hat Enterprise Linux or Ubuntu), or OutOfMemoryException errors appear in /var/log/rhn/rhn_taskomatic_daemon.log.

Value default

4096 MiB

Value recommendation

4096-16384 MiB

Location

/etc/rhn/rhn.conf

Example

taskomatic.java.maxmemory = 8192

After changing

Check memory usage.

More information

man rhn.conf

Description

The number of Taskomatic worker threads. Increasing this value allows Taskomatic to serve more clients in parallel.

Tune when

Client count increases significantly

Value default

20

Value recommendation

20-200

Location

/etc/rhn/rhn.conf

Example

org.quartz.threadPool.threadCount = 100

After changing

Check hibernate.c3p0.max_size and thread_pool for adjustment

More information

http://www.quartz-scheduler.org/documentation/2.4.0-SNAPSHOT/configuration.html

Description

Cycle time for Taskomatic. Decreasing this value lowers the latency of Taskomatic.

Tune when

Client count is in the thousands.

Value default

5000 ms

Value recommendation

1000-5000 ms

Location

/etc/rhn/rhn.conf

Example

org.quartz.scheduler.idleWaitTime = 1000

More information

http://www.quartz-scheduler.org/documentation/2.4.0-SNAPSHOT/configuration.html

Description

Number of Taskomatic threads dedicated to sending commands to Salt clients as a result of actions being executed.

Tune when

Client count is in the thousands.

Value default

1

Value recommendation

1-10

Location

/etc/rhn/rhn.conf

Example

taskomatic.com.redhat.rhn.taskomatic.task.MinionActionExecutor.parallel_threads = 10

Description

Number of Taskomatic threads dedicated to sending commands to Salt SSH clients as a result of actions being executed.

Tune when

Client count is in the hundreds.

Value default

20

Value recommendation

20-100

Location

/etc/rhn/rhn.conf

Example

taskomatic.com.redhat.rhn.taskomatic.task.SSHMinionActionExecutor.parallel_threads = 40

Description

Maximum number of PostgreSQL connections simultaneously available to both Tomcat and Taskomatic. If any of those components requires more concurrent connections, their requests will be queued.

Tune when

java.message_queue_thread_pool_size or maxThreads increase significantly, or when org.quartz.threadPool.threadCount has changed significantly. Each thread consumes one connection in Taskomatic and Tomcat, having more threads than connections might result in starving.

Value default

20

Value recommendation

100 to 200, higher than the maximum of java.message_queue_thread_pool_size + maxThreads and org.quartz.threadPool.threadCount

Location

/etc/rhn/rhn.conf

Example

hibernate.c3p0.max_size = 100

After changing

Check max_connections for adjustment.

More information

https://www.mchange.com/projects/c3p0/#maxPoolSize

Description

The maximum amount of memory that the rhn-search service can use.

Tune when

Client count increases significantly, and OutOfMemoryException errors appear in journalctl -u rhn-search.

Value default

512 MiB

Value recommendation

512-4096 MiB

Location

/etc/rhn/rhn.conf

Example

rhn-search.java.maxmemory = 4096

After changing

Check memory usage.

Description

The amount of memory reserved for PostgreSQL shared buffers, which contain caches of database tables and index data.

Tune when

RAM changes

Value default

25% of total RAM

Value recommendation

25-40% of total RAM

Location

/var/lib/pgsql/data/postgresql.conf

Example

shared_buffers = 8192MB

After changing

Check memory usage.

More information

https://www.postgresql.org/docs/15/runtime-config-resource.html#GUC-SHARED-BUFFERS

Description

Maximum number of PostgreSQL connections available to applications. More connections allow for more concurrent threads/workers in various components (in particular Tomcat and Taskomatic), which generally improves performance. However, each connection consumes resources, in particular work_mem megabytes per sort operation per connection.

Tune when

hibernate.c3p0.max_size changes significantly, as that parameter determines the maximum number of connections available to Tomcat and Taskomatic

Value default

400

Value recommendation

Depends on other settings, use /usr/lib/susemanager/bin/susemanager-connection-check to obtain a recommendation.

Location

/var/lib/pgsql/data/postgresql.conf

Example

max_connections = 250

After changing

Check memory usage. Monitor memory usage closely before and after the change.

More information

https://www.postgresql.org/docs/15/runtime-config-connection.html#GUC-MAX-CONNECTIONS

Description

The amount of memory allocated by PostgreSQL every time a connection needs to do a sort or hash operation. Every connection (as specified by max_connections) might make use of an amount of memory equal to a multiple of work_mem.

Tune when

Database operations are slow because of excessive temporary file disk I/O. To test if that is happening, add log_temp_files = 5120 to /var/lib/pgsql/data/postgresql.conf, restart PostgreSQL, and monitor the PostgreSQL log files. If you see lines containing LOG: temporary file: try raising this parameter’s value to help reduce disk I/O and speed up database operations.

Value recommendation

2-20 MB

Location

/var/lib/pgsql/data/postgresql.conf

Example

work_mem = 10MB

After changing

check if the Uyuni Server might need additional RAM.

More information

https://www.postgresql.org/docs/15/runtime-config-resource.html#GUC-WORK-MEM

Description

Estimation of the total memory available to PostgreSQL for caching. It is the explicitly reserved memory (shared_buffers) plus any memory used by the kernel as cache/buffer.

Tune when

Hardware RAM or memory usage increase significantly

Value recommendation

Start with 75% of total RAM. For finer settings, use shared_buffers + free memory + buffer/cache memory. Free and buffer/cache can be determined via the free -m command (free and buff/cache in the output respectively)

Location

/var/lib/pgsql/data/postgresql.conf

Example

effective_cache_size = 24GB

After changing

Check memory usage

Notes

This is an estimation for the query planner, not an allocation.

More information

https://www.postgresql.org/docs/15/runtime-config-query.html#GUC-EFFECTIVE-CACHE-SIZE

Description

The number of worker threads serving Salt API HTTP requests. A higher number can improve parallelism of Uyuni Server-initiated Salt operations, but will consume more memory.

Tune when

java.message_queue_thread_pool_size or org.quartz.threadPool.threadCount are changed. Starvation can occur when there are more Tomcat or Taskomatic threads making simultaneous Salt API calls than there are Salt API worker threads.

Value default

100

Value recommendation

100-500, but should be higher than the sum of java.message_queue_thread_pool_size and org.quartz.threadPool.threadCount

Location

/etc/salt/master.d/susemanager.conf, in the rest_cherrypy section.

Example

thread_pool: 100

After changing

Check worker_threads for adjustment.

More information

https://docs.saltproject.io/en/latest/ref/netapi/all/salt.netapi.rest_cherrypy.html#performance-tuning

Description

The number of salt-master worker threads that process commands and replies from minions and the Salt API. Increasing this value, assuming sufficient resources are available, allows Salt to process more data in parallel from minions without timing out, but will consume significantly more RAM (typically about 70 MiB per thread). Setting this value to very high values could cause opposite effect as the workers will compete to each other for the CPU resources and the performance could be dropped significantly.

Tune when

Client count increases significantly, thread_pool increases significantly, or SaltReqTimeoutError or Message timed out errors appear in /var/log/salt/master could be a sign of too low or too high value of this parameter.

Value default

8

Value recommendation

8-32, depending on the number of the CPU cores available for the server, it is recommended to keep the value slightly less than the number of CPU cores.

Location

/etc/salt/master.d/tuning.conf

Example

worker_threads: 16

After changing

Check memory usage. Monitor memory usage closely before and after the change. It makes sense to monitor the salt-master stats event by enabling master_stats and adjusting master_stats_event_iter to fine tune the value of this parameter.

More information

https://docs.saltproject.io/en/latest/ref/configuration/master.html#worker-threads

Description

Determines whether the master will fire authentication events. Authentication events are fired when a minion performs an authentication check with the master. It helps to reduce the number of events published with the Salt Master Event Publisher and reduce the workload on Event Publisher subscribers.

Tune when

Large amount of salt/auth events published in the Salt event bus, which in most cases are useless for the subscribers.

Value default

True

Value recommendation

False

Location

/etc/salt/master.d/tuning.conf

Example

auth_events: False

More information

https://docs.saltproject.io/en/latest/ref/configuration/master.html#auth-events

Description

Determines whether the master will fire minion data cache events (minion/refresh/*). Minion data cache events are fired when a minion requests a minion data cache refresh. It helps to reduce the number of events published with the Salt Master Event Publisher and reduce the workload on Event Publisher subscribers.

Tune when

Large amount of minion/refresh/* events published in the Salt event bus, which in most cases are useless for the subscribers.

Value default

True

Value recommendation

False

Location

/etc/salt/master.d/tuning.conf

Example

minion_data_cache_events: False

More information

https://docs.saltproject.io/en/latest/ref/configuration/master.html#minion-data-cache-events

Description

The maximum number of outstanding messages sent by salt-master. If more than this number of messages need to be sent concurrently, communication with clients slows down, potentially resulting in timeout errors during load peaks.

Tune when

Client count increases significantly and Salt request timed out. The master is not responding. errors appear when pinging minions during a load peak.

Value default

1000

Value recommendation

10000-100000

Location

/etc/salt/master.d/tuning.conf

Example

pub_hwm: 10000

More information

https://docs.saltproject.io/en/latest/ref/configuration/master.html#pub-hwm, https://zeromq.org/socket-api/#high-water-mark

Description

The maximum number of allowed client connections that have started but not concluded the opening process. If more than this number of clients connects in a very short time frame, connections are dropped and clients experience a delay re-connecting.

Tune when

Client count increases significantly and very many clients reconnect in a short time frame, TCP connections to the salt-master process get dropped by the kernel.

Value default

1000

Value recommendation

1000-5000

Location

/etc/salt/master.d/tuning.conf

Example

zmq_backlog: 2000

More information

https://docs.saltproject.io/en/latest/ref/configuration/master.html#zmq-backlog, http://api.zeromq.org/3-0:zmq-getsockopt (ZMQ_BACKLOG)

Description

How aggressively the kernel moves unused data from memory to the swap partition. Setting a lower parameter typically reduces swap usage and results in better performance, especially when RAM memory is abundant.

Tune when

RAM increases, or swap is used when RAM memory is sufficient.

Value default

60

Value recommendation

1-60. For 128 GB of RAM, 10 is expected to give good results.

Location

/etc/sysctl.conf

Example

vm.swappiness = 20

More information

https://documentation.suse.com/sles/15-SP4/html/SLES-all/cha-tuning-memory.html#cha-tuning-memory-vm

Description

Determines whether the salt-broker service should wait for backend sockets to be connected before opening the sockets for listening for connections from salt-minions. When enabled, it helps to prevent collecting ZeroMQ messages with the internal buffers of the sockets and pushing them to the salt-master once connection is restored.

Tune when

Unstable connectivity between the Uyuni Proxy and the Uyuni Server.

Value default

False

Value recommendation

True

Location

/etc/salt/broker

Example

wait_for_backend: True

More information

Proxies Connectivity

Description

The tcp keepalive interval to set on TCP ports. This setting can be used to tune Salt connectivity issues in messy network environments with misbehaving firewalls.

Tune when

Unstable connectivity between managed clients and the Uyuni Proxy or the Uyuni Server.

Value default

True

Value recommendation

True

Location

/etc/venv-salt-minon/minion.d/tuning.conf or /etc/salt/minion.d/tuning.conf, depending on the minion type.

Example

tcp_keepalive: True

After changing

Check Minions Connectivity for more details to fine tune extra keepalive parameters.

More information

https://docs.saltproject.io/en/latest/ref/configuration/minion.html#tcp-keepalive, Minions Connectivity