Version 1.14.17 of the Solana Labs validator client introduces a command line interface (CLI) option --enable-accounts-disk-index that enables storage of the AccountsIndex on disk rather than in RAM. This option can be enabled on validator start-up and reduces the RAM usage of a mainnet-beta validator by about 40-50GB as of May 4th 2023. It reduces RAM usage by storing the Accounts Index on disk, and using an in-memory least recently used (LRU) cache to store the most actively accessed accounts.
This feature is not enabled by default. It is recommended only for validators with their Ledger folder backed by 2 performant NVMe SSDs. Validators with only one SSD or older style SSDs may encounter performance degradation evident by disk IO reads/writes increasing significantly. This is particularly evident during startup/catchup such that the validators do not catch up quickly.