By default Bitbucket Server is installed with a configured maximum heap size of 768m. This allocates 512m to the old generation and the remainder to the young generation (eden, survivor).

If some plugins are installed, coupled with the base memory usage of the product, it is possible to fill the old generation. In this regime the GC can performance consecutive full, and very poor performance results.

In Bitbucket Server 4.10 we move from the standard throughput collector to the G1 collector. This collector has been demonstrated to provide superior performance in this scenario. It is also slated to be the default collector in Java 9.