PostgreSQL: How much memory should I allocate as ramdisk for "pg_stat_tmp"?

We have been facing a problem in an Azure VM running PostgreSQL13 where a recurring issue of disk availability causing statistics collector process to stall for few seconds followed by slow queries. After searching few threads I have found that changing pg_stat_tmp to ramdisk could resolve this and maybe improve performance as well. What would be the best size to allocate ramdisk? Is there any way to calculate? What could possibly happen if collector run out of this allocated memory?