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Java applications like JIRA and Confluence run in a "Java virtual machine" (JVM), instead of directly within an operating system. When started, the Java virtual machine is allocated a certain amount of memory, which it makes available to applications like JIRA. By default, Java virtual machines are allocated 64Mb of memory, no matter how many gigabytes of memory your server may actually have available. 64Mb is inadequate for medium to large JIRA installations, and so this needs to be increased. Seeing OutOfMemoryErrors in the logs is symptomatic of this.

(warning) This page addresses how to increase Heap Space memory. Confirm that you're not receiving Perm Gen or GC Overhead errors.

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Assess Root Cause

Note

Often, there is a root cause for OutOfMemory Errors that may be better to address than just increasing memory. See JIRA Crashes Due to 'OutOfMemoryError Java heap space' for a discussion.

Determine JIRA usage patterns

In JIRA, go to Administration > System > System Info, and look at the memory graph during times of peak usage:

(info) This server has been allocated a maximum of 650Mb and a minimum of 256m. You can see the minimum displayed here; if you're trying to see whether your settings are being picked up, this is where to look. Of this, JIRA has reserved 543Mb, or which 310Mb is actually in use (this JIRA instance has about 6000 issues). If this JIRA instance were running out of memory, it would have reserved the maximum available (650Mb), and would be using an amount close to this.

Determine available system memory

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From the Close Programs Dialogue (Press ctrl-alt-delete), select the Performance tab:

(info) The amount marked Available is the amount in kilobytes you have free to allocate to JIRA. On this server we should allocate at most 214Mb.

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Run cat /proc/meminfo to view the memory usage.

Setting the -Xmx above the available amount on the server runs the risk of OutOfMemoryErrors due to lack of physical memory. If that occurs the system will use swap space, which greatly decreases performance.

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Guidance

As a rule of thumb, if you have fewer than 5000 issues, JIRA should run well with the default 768MB. Granting JIRA too much memory can impact performance negatively, so it is best to start with 768Mb and make modest increases as necessary. As another data point, 40,000 works well with 768MB to 1GB.

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