这个需要根据你实际使用的情况来决定。
请参考官方的文章:
As a rule of thumb, if you have fewer than 5000 issues, JIRA applications should run well with the default 768 MB. Granting JIRA applications too much memory can impact performance negatively, so it is best to start with 768 MB, and make modest increases as necessary.
As another data point, 40,000 works well with 768 MB to 1 GB.
从官方的说法来说 1G 基本上是绰绰有余了。