I installed new search service application using powershell. "sp_sapool" is the service application pool account which i used. Everything installed fine. Topology is activated, i changed default content access account to be "sp_crawl". But when i changed under "Configure service accounts" following: "Windows service - Search Host Controller" and "SharePoint Server Search" to use "sp_search" account, which is normal domain user account without any rights, my topology is not showing up anymore, instead it says "Unable to retrieve topology component health states. This may be because the admin component is not up and running." Do i have to assign some db rights for the "sp_search" account?
Use the same service account for your 'SharePoint Server Search' service as you do for all other services (MMS, UPS, etc.). This will maximize performance/reduce memory usage. Do not change the Search Host Controller away from the Farm Administrator account.