Memory Configuration

Memory Settings

Running the CData Virtuality Server requires a considerable amount of memory. Providing and configuring the memory is crucial for a fast and stable server installation, especially when the CData Virtuality Server has to perform many operations or handle vast amounts of data.

Memory for the CData Virtuality Server is configured via JVM-based memory settings and BufferManager settings.

The CData Virtuality Server has an auto-adjust mechanism to configure memory usage according to your local resources.

Auto-Adjusting

The CData Virtuality Server startup script configures memory settings as indicated in section "Memory Settings Recommendations" automatically on bootstrap.

You can configure the script using the analytic_storage_on_different_host_dv parameter in %pathToDVserver%/bin/standalone.conf (Linux)/ %pathToDVserver%\bin\standalone.conf.bat (Windows) files:

Parameter	Value
`analytic_storage_on_different_host_dv`	`0` (default) if the analytical storage and the CData Virtuality Server are on the same host `1` if the analytical storage and the CData Virtuality Server use different hosts

Configuration Files

You can find memory settings in the following files:

Operating System	File	Comment
Linux	%pathToDVserver%/bin/standalone.conf	Contains JVM-based memory settings
Windows	%pathToDVserver%\bin\standalone.conf.bat	Contains JVM-based memory settings
Linux/Windows	%pathToDVserver%/standalone/configuration/dvserver-standalone.xml	Contains memory settings of the application server

On Windows platforms, it is possible to configure JVM memory settings in different files.

We do not recommend doing this! If memory settings are found in different locations, the server will use the ones read last.

If you find duplicate startup options in the boot.log file, remove memory settings from all locations other then standalone.conf.bat. They may reside in the following places:

%pathToDVserver%\bin\standalone.bat
%pathToDVserver%\bin\service.bat

JVM Settings

You can configure the memory settings of the CData Virtuality Server process via the JVM settings. It is important to properly configure the amount of heap memory and allocated total memory.

JVM option	Example	Comment
`-Xms`	`-Xms8912M`	Minimum amount of heap memory	`-Xms` and `-Xmx` may be set to equal values
`-Xmx`	`-Xmx8912M`	Maximum amount of heap memory	`-Xms` and `-Xmx` may be set to equal values
`-XX:MaxDirectMemorySize`	`-XX:MaxDirectMemorySize=6G`	Maximum total size for new Java I/O package direct buffer allocations	`-XX:MaxDirectMemorySize` (JVM setting) may not be less than the sum of `memory-buffer-space` and `max-storage-object-size`
`-XX:ReservedCodeCacheSize`	`-XX:ReservedCodeCacheSize=128m`	Size of cache used to store code which Java's compiler will access

BufferManager Settings

BufferManager is responsible for tracking memory and disk usage by the CData Virtuality Server. Configuring the BufferManager properly is one of the most important parts of ensuring high performance.

Settings for the BufferManager are stored in the %pathToDVserver%\standalone\configuration\dvserver-standalone.xml file in the CData Virtuality Server folder, section buffer-service. Here is an example of how they may look:

XML

<buffer-service memory-buffer-off-heap="true" max-storage-object-size="134217728"/>

Application Server Setting	Default Value	Description	Remarks
`max-reserve-kb`	`-1`	Total size of batches that the BufferManager can hold in memory. The default value `-1` will auto-calculate a typical max based upon the max heap available to the VM	Specified in KB without a measurement unit
`max-processing-kb`	`-1`	Total size of batches that can be used by active plans regardless of the memory held based on `max-reserve-kb`. The default value of `-1` will auto-calculate a typical max based upon the max heap available to the VM and max active plan	Specified in KB without a measurement unit
`max-file-size`	2048 (in MB)		Specified in MB without a measurement unit
`max-buffer-space`	51200 (in MB, i.e., 50 GB)		Specified in MB without a measurement unit
`max-storage-object-size`	134217728 (in bytes)	Sizing for `max-storage-object-size` is in terms of serialized size, which will be much closer to the raw data size than the Java memory footprint estimation used for `max-reserve-kb`. `max-storage-object-siz`e should not be set too large relatively to `memory-buffer-space` since it will reduce the performance of the memory buffer. The memory buffer supports only one concurrent writer for each `max-storage-object-size` of `memory-buffer-space`	Specified in bytes without a measurement unit
`memory-buffer-off-heap`	`TRUE`	Setting `memory-buffer-off-heap` to `TRUE` will allocate the CData Virtuality Server memory buffer off-heap. Depending on whether your system runs only the CData Virtuality Server and the amount of system memory available, this may be preferable to on-heap allocation. The primary benefit is additional memory usage without additional garbage collection tuning. This becomes especially important in situations where more than 32 GB of memory is desired for the VM. Note that when using off-heap allocation, the memory must still be available to the java process and that setting the value of `memoryBufferSpace` too high may cause the VM to swap rather than reside in memory.
`memory-buffer-space`	`-1`	Determines how much memory exactly the server can use for buffers/`memory-buffer-space` setting controls the amount of on or off-heap memory allocated as byte buffers for use by the buffer manager. The default value `-1` automatically determines a setting based upon whether it is on or off-heap, and the value for `max-reserve-kb`. You can use the buffer manager memory buffer to access system memory without allocating it to the heap. buffer-service element of dvserver-standalone.xml	Specified in MB without a measurement unit

In systems where extensive intermediate results are normal (scrolling cursors or sorting over millions of rows), you can consider increasing max-processing-kb and decreasing max-reserve-kb so that each request has access to an effectively smaller buffer space. Each intermediate result buffer, temporary LOB, and the temporary table are stored in their own set of buffer files, where an individual file is limited to max-file-size megabytes. Consider increasing the storage space available to all such files if your installation uses internal materialization, makes heavy use of SQL/XML, or processes large row counts.

Recommendations

General Recommendations

	Analytical Storage on
Setting	same	different
	host as DataVirtuality Server
`-XX:MaxDirectMemorySize`	65–75 % of available RAM	80–85 % of available RAM
`-Xms, -Xmx`	60% of `MaxDirectMemorySize`
`-XX:MaxPermSize`	10 % of `Xms`	14 % of `Xms`
`-XX:UseLargePages`	yes, if `Xms` >= 12 GB RAM
`memory-buffer-space`	50 % of `MaxDirectMemorySize`
`-XX:ReservedCodeCacheSize`	256 MB RAM

Example: Recommendations for a System with 32 GB of RAM

	Analytical Storage on
Setting	same	different
	host as CData Virtuality Server
`-XX:MaxDirectMemorySize`	20 GB	27 GB
`-Xms, -Xmx`	12 GB	16 GB
`-XX:MaxPermSize`	512 MB	768 MB
`-XX:UseLargePages`	`-UseLargePages`	`+UseLargePages`
`memory-buffer-space`	10240	13312
`-XX:ReservedCodeCacheSize`	256 MB

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