Tuning the server

Java Virtual Machine (JVM) Tuning

Java version
Servoy supports both Java 5 and Java 6 (for the Application Server, the Smart Client and Servoy Developer). As Java 6 has numerous performance improvements, it is preferred over Java 5.

If the hardware in which Servoy is running is 64bit, make sure to also run a 64 bit Java Virtual Machine. When in doubt which version is used, check the Servoy Admin page, under "Servoy Server Home" > "Servoy Server Status" > "JVM Information":

• 64 bit: java.vm.name=Java HotSpot(TM) 64-Bit Server VM
• 32 bit: java.vm.name=Java HotSpot(TM) Client VM

Java Virtual Machine Server mode
Java has 2 distinct operating modes: client mode and server mode. When running in server mode, the startup of the Java process will take longer and initial execution of code will be slower, but after a while the application will perform faster. The server mode is best suited for the Servoy Application Server.

Whether or not a Java Virtual Machine supports client and/or server mode depends on the hardware, see http://download.oracle.com/javase/6/docs/technotes/guides/vm/server-class.html.

If the JVM supports servermode, it will automatically detect if the machine it is running on is a "capable" machine and automatically run in server or client mode depending. The definition of "capable" may differ from Java version to Java version. For Java 5/6 this means a 2CPU, 2Gb memory machine.

Checking whether or not a Servoy Application Server runs in client or server mode can be seen on the Servoy Admin page, under "Servoy Server Home" > "Servoy Server Status" > "JVM Information":

• Server mode: java.vm.name=Java HotSpot(TM) 64-Bit Server VM
• Client mode: java.vm.name=Java HotSpot(TM) Client VM

It is possible to enforce the Servoy Application Server to run in server mode (assuming the JVM is capable to operate in server mode), an extra startup argument can be added to the startup of the Servoy Application Server.

In servoy_server.sh/bat:

java -server -Djava.awt.headless=true .....

When using the Service wrapper:

# Java Additional Parameters
wrapper.java.additional.1=-Djava.awt.headless=true
wrapper.java.additional.2=-Duser.dir="C:\Servoy\application_server"
wrapper.java.additional.3=-XX:MaxPermSize=128m
wrapper.java.additional.4=-server

Memory

Processes in Java, like the Servoy Application Server, need to be told explicitly the maximum of memory they are allowed to use. This setting, the maximum heap size, is important to adjust to the load the Servoy Application Server is to handle.

The maximum heap size setting is located in {servoy_install}/application_server/servoy_server.sh/.bat, through the "Xmx" setting.

When the Application Server is started as a Service the setting can be found in {servoy_install}/application_server/service/wrapper.conf, by the name of "wrapper.java.maxmemory".

By default the maximum heap size is set to 256MB. This setting should be changed when:

• The actual used memory is >= 70% of the specified maximum. The actually used memory can be found on the main page of the Admin page, under System Information, like: Heap memory: allocated=549184K, used=371473K, max=699072K
• When the expected client load will exceed the maximum: As a rule of thumb:
  • Smart Client: assume a memory usage of about 600kb for each Smart Client. NOTE: When the Servoy HTTP Tunnel is used, assume 900kb per Client.
  • All other type of Clients (Web, Headless, Batch): the required memory for each client depends on the size and design of the solution, but should be in the order of magnitude of a couple of Mb per Client.
• When there is plenty of free real memory available on the OS level. Java processes in general perform better when not having memory constraints. For example, when 2Gb free real memory is left, add the 2Gb to the maximum heap size. The Java process will only take what it needs.

Database Connection Pool Tuning

The Servoy Application Server uses a pool of database connections per configured Database Server. 

The maximum number of active and idle connections within a pool is configurable to preserve resources. For example, a single connection could easily take up a couple of Mb, both on the Servoy Application Server side, as well as on the database engine side.

The settings are configurable on the Servoy Admin page, under Database Servers:

• Maximum connections active: the maximum number of connections that can be created within the pool.
  If set too low, handling requests towards the database might slow down, as one request needs to wait until another request is processed and the connection is returned to the pool
  If set too high, the exceptions might occur if the database cannot handle that many concurrent connections or if more memory is required than is available
• Maximum connections idle: the maximum number of inactive or idle connections in the pool
  Active connections that are done processing a request are returned to the connection pool as idle connections. If the number of idle connections goes over the maximum, the connections are removed.
  As instantiating new connections takes time, the value shouldn't be too low. On the other side idle connections take up resources, so the number shouldn't be too high either.

The maximum number of active connections is also limited by the maximum number of connections the database itself is configured to allow. For the bundled PostgreSQL database engine, the maximum is 100 connections. However, these 100 connections are for all connections made to the database instance. This means that if there are multiple Database Servers defined on the Servoy Application Server which are all hosted on the same database instance, the max. 100 connections are for all Database Servers combined. This must be taken into account when setting up the maximun number of active connections.

By default, the maximum active connections setting is set to 10. This could be too low when serving may clients from one Application Server or when the clients do many requests to the database. As rule of thumb, if the actual used active connection regularly goes above 70% of the maximum a higher number of maximum active connections should be configured.

Database Tuning

Architecture

In order to get the best possible performance, the communication between the Servoy Application Server and the database needs to be as fast as possible. The fastest option would be installing the database engine and the Servoy Application Server on the same machine, whether or not this is possible depends on the dimensions of the physical server and the resource requirements of both the database engine and the Servoy Application Server.

When opting for dedicated servers for both the database engine and the Servoy Application Server, the connection between them should be as fast as possible, preferably a direct 1Gb cable connection between the two machines.

Database tuning 

When experiencing performance issues the "Performance Data" page of the Servoy Admin page can be analysed to find slow performing SQL statements, or SLQ statements that are fired often.

The page provides an overview of all queries fired at the database. The performance data is sorted by the total time taken to perform the query, being the result of the average time * number of executions.

At any given time regular SQL statements (Type = Relation, Load foundset) should have an average execution time below 25 milliseconds.

Especially for SQL statements that are fired often and take up significant time it should be checked if it's possible to optimize the database, for example by creating the relevant indexes. 

Web Client Settings Tuning

servoy.webclient.templates.use_local_ids

For the Web Client, Servoy generates HTML markup. In order for Servoy to dynamically update only parts of the UI through Ajax, each object in the HTML Markup receives a unique ID. This ID is also placed in the editable Web Client templates.

Servoy has 2 modes for generating the ID's:

• Using unique identifiers that are part of the internal design of the Solution created with Servoy. These ID's, as they are part of the solution design, are the same on any Servoy Application Server where the solution is imported. 
• Using local identifiers. These identifiers are generated at runtime and thus differ per installation and session.

The advantage of the local identifiers are that they are shorter in length, thus bring down the weight of the generated HTML markup. The advantage of the unique identifiers is that they are the same on any server where the solution is running.

If templates are used to modify the generated HTML markup for Web Clients, then the unique identifiers are to be used, in order to maintain the link between the identifiers in the edited templates and the identifiers used at runtime. Otherwise the local identifiers can be used.

By default a Servoy Application Server uses the unique identifiers. Enabling the use of local identifiers can be done by setting the servoy.webclient.templates.use_local_ids option on the Servoy Admin page to true (located under Servoy Settings > Web Client settings) 

Content compression

In order to minimize the size of the content that the browser has to download for the Web Client, it's possible to turn on compression. The Servoy Application Server is currently not configured to automatically compress the content. 

Compression can be done by the Apache Tomcat instance that is part of the Servoy Application Server, or can be done by an HTTP server that is in front of the Servoy application Server, like an Apache HTTPD Server. 

In order to enable compression in the Tomcat instance that is part of the Servoy Application Server, open the file "server.xml" located in {servoy_install}application_server\server\conf\. and locate the Connector:

<Connector port="8080"
  protocol="HTTP/1.1"
  maxThreads="500" connectionTimeout="60000"
  redirectPort="8443" useBodyEncodingForURI="true" />

and add the following atttributes:

• compressableMimeType="text/html,text/xml,text/css,text/javascript,text/plain" 
• compression="on"
• compressionMinSize="2048" 

so the connector is configured like this:

<Connector port="8080"
  protocol="HTTP/1.1"
  maxThreads="500" connectionTimeout="60000"
  redirectPort="8443" useBodyEncodingForURI="true"
  compressableMimeType="text/html,text/xml,text/css,text/javascript,text/plain" compression="on"
  compressionMinSize="2048"/>

Save the edits and restart the Servoy Application Server to let the configuration changes take effect.

It is also possible to handle the compression outside of the Servoy Application Server, for example in an Apache HTTPD Server placed between the Servoy Application Server and the outside world. The advantage of this is that Tomcat's compression options are limited, so an external HTTP server offers more options.

When it comes to Apache HTTPD server, there are two options:

1. Compression using mod_deflate
2. Compression using gzip

When it comes to compression, there are two factors that come into play, the time it takes to do the actual compression and the rate of compression achieved, resulting in quicker downloads to the browser due to smaller size. This is primary difference between mod_deflate and gzip in Apache HTTPD: while gzip gets a better compression rate than mod_deflate, it takes more time and CPU to perform the compression. In the case of Servoy Web Clients, that, due to it's Ajax driven design, performs a lot (albeit small) requests to the server, the overall performance will be better using mod_deflate.

Details on setting up mod_deflate on an Apache HTTPD server can be found here: http://httpd.apache.org/docs/2.0/mod/mod_deflate.html

Servoy Application Server log

At all times try to keep the Server log free from javascript application errors/excpetions, all application exceptions point to possible problems inside the application.

• Out of memory errors means the heap size is configured to small.
• Nullpointer errors indicate Servoy codebase problems, incase these are noticed file a support case containing the log entry.
• Network error are only listed as non critical (orange) which may point to (possible) networks (config) problems, when many errors are continuous listed these should definitely be investigated.