FIO does not require users to purchase RAM. Instead, each FIO action increments RAM independently. Because of the FIO modifications to RAM limits developers must determine the "RAM Bump" for each action.

In general:

Only include a RAM bump for actions that increase memory allocation
Actions that remove content from memory do NOT need a RAM bump

There are three use cases for allocating RAM:

Determining RAM for a new action that accepts multiple, similar data fields
Determining RAM for a new action with a fixed set of data fields
Determining RAM for actions where the size is uncertain

Determining RAM for a new action that accepts multiple, similar data fields

Examples: addaddress, addnft

1. Add maximum sized content for all variables

2. Create a transaction for the new action using the max size content for parameters

In this example addnft is called with maximum content in the parameters. The addnft action can be called with up to 3 NFTs in a single call. Because each NFT has the same set of parameters, we will use the RAM estimate when adding a single NFT and, in the contract code, bump different multiples of the RAM bump amount depenging on how many NFTs are added. This, if a user adds 3 NFTs in a single call, they would get allocated addnft RAM bump value x 3.

./clio -u http\://localhost:8889 push action -j fio.address addnft '{"fio_address":"12345678901234567890123456789012345678901234567890123@1234567890","nfts":[{"chain_code":"ETH4567890","contract_address":"J1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567","token_id":"J234567890123456789012345678901234567890123456789012345678901234","url":"http://longurl.com/jasdfghjkljasdfghjkljasdfghjkljasdfghjkljasdfghjkl","hash":"16E4561A0B5352DB93C7B2705FEFC6A632994CC874ABF0F2D64F2DC72D820CB1","metadata":"J234567890123456789012345678901234567890123456789012345678901234"}],"max_fee":40000000000,"actor":"o2ouxipw2rt4","tpid":"12345678901234567890123456789012345678901234567890123@1234567890"}' -p o2ouxipw2rt4@active

3. Note the account_ram_deltas > delta size in the transaction response

In this example "delta": 1367 is returned

{
  "transaction_id": "884a0a9be9fb2c986cfb6ec20a5eeaed2180b8652dc7c56ca22fbf61a9263f6c",
  "processed": {
    "id": "884a0a9be9fb2c986cfb6ec20a5eeaed2180b8652dc7c56ca22fbf61a9263f6c",
    "block_num": 25012,
    "block_time": "2021-09-30T21:41:26.500",
    "producer_block_id": null,
    "receipt": {
      "status": "executed",
      "cpu_usage_us": 4606,
      "net_usage_words": 81
    },
    "elapsed": 4606,
    "net_usage": 648,
    "scheduled": false,
    "action_traces": [{
        "receipt": {
          "receiver": "fio.address",
          "response": "{\"status\": \"OK\",\"fee_collected\":0}",
          "act_digest": "e847dce232d9a574c3fa3f72086a5e1f5555c7cf04b63ccd92ac2a402300a39b",
          "global_sequence": 25881,
          "recv_sequence": 98,
          "auth_sequence": [[
              "o2ouxipw2rt4",
              17
            ]
          ],
          "code_sequence": 2,
          "abi_sequence": 2
        },
        "receiver": "fio.address",
        "act": {
          "account": "fio.address",
          "name": "addnft",
          "authorization": [{
              "actor": "o2ouxipw2rt4",
              "permission": "active"
            }
          ],
          "data": {
            "fio_address": "12345678901234567890123456789012345678901234567890123@1234567890",
            "nfts": [{
                "chain_code": "ETH4567890",
                "contract_address": "J1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567",
                "token_id": "J234567890123456789012345678901234567890123456789012345678901234",
                "url": "http://longurl.com/jasdfghjkljasdfghjkljasdfghjkljasdfghjkljasdfghjkl",
                "hash": "16E4561A0B5352DB93C7B2705FEFC6A632994CC874ABF0F2D64F2DC72D820CB1",
                "metadata": "J234567890123456789012345678901234567890123456789012345678901234"
              }
            ],
            "max_fee": 40000000000,
            "actor": "o2ouxipw2rt4",
            "tpid": "12345678901234567890123456789012345678901234567890123@1234567890"
          },
          "hex_data": ...
        },
        "context_free": false,
        "elapsed": 3803,
        "console": "TRX SIZE604\n",
        "trx_id": "884a0a9be9fb2c986cfb6ec20a5eeaed2180b8652dc7c56ca22fbf61a9263f6c",
        "block_num": 25012,
        "block_time": "2021-09-30T21:41:26.500",
        "producer_block_id": null,
>       "account_ram_deltas": [{
>           "account": "o2ouxipw2rt4",
>           "delta": 1367
          }
        ],

4. Multiply the amount by 1.5 to add a buffer

1367 * 1.5 = 2050

5. Round to the nearest value that is divisible by 512

round(2050 / 512) = round(4.01) = 4
addnft RAM = 4 * 512 = 2048

So, 2048 would be the suggested RAM bump for each NFT added using addnft.

Determining RAM for a new action with a fixed set of data fields

Examples: trnsfiopubky, newfundsreq

Determining RAM for a new action with a fixed set of data fields is similar to the above example except that the same RAM bump is always allocated regardless of what data is sent in.