How to Change the Number of Threads Used for Attachment Reindexing
Use Case
By default, the number of threads used for attachment reindexing is 4 threads on Confluence versions until 7.13. Having more threads on this process will be useful to increase speed of indexing given that the machine/processor is capable on doing so. Please be cautious while increasing this number to ensure that we do not set it high enough to cause performance issues. Kindly validate and test these increased settings on a test environment before applying this on production.
Starting on Confluence version 7.14, the default number of threads used for attachment reindexing is the larger value between 4 and a calculation that considers the number of processors and the available free memory in the JVM.
Resolution
Add the JVM parameter -Dreindex.attachments.thread.count=10. (see Configuring System Properties for tips on how to set an environment variable)
Note: The above example will set 10 threads for attachment reindexing process.
Number of threads used for Content reindexing
If you are looking for a JVM parameter to change the number of threads used for Content reindexing instead, take a look at "Poor performance while rebuilding the index" section in the Knowledge Base article
Content Index Administration - make sure to select the appropriate Confluence version on the combo box at the top right of the page.