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Low-level fees overview

caution

This section describes instructions and manuals for interacting with TON at a low level.

caution

Here you will find the raw formulas for calculating commissions and fees on TON.

However, most of them are already implemented through opcodes! So, you use them instead of manual calculations.

This document provides a general idea of transaction fees on TON and particularly computation fees for the FunC code. There is also a detailed specification in the TVM whitepaper.

Transactions and phases​

As was described in the TVM overview, transaction execution consists of a few phases. During those phases, the corresponding fees may be deducted. There is a high-level fees overview.

Storage fee​

TON validators collect storage fees from smart contracts.

Storage fees are collected from the smart contract balance at the Storage phase of any transaction due storage payments for the account state (including smart-contract code and data, if present) up to the present time. The smart contract may be frozen as a result.

It’s important to keep in mind that on TON you pay for both the execution of a smart contract and for the used storage (check @thedailyton article). storage fee depends on you contract size: number of cells and sum of number of bits from that cells. Only unique hash cells are counted for storage and fwd fees i.e. 3 identical hash cells are counted as one. It means you have to pay a storage fee for having TON Wallet (even if it's very-very small).

If you have not used your TON Wallet for a significant period of time (1 year), you will have to pay a significantly larger commission than usual because the wallet pays commission on sending and receiving transactions.

Formula​

You can approximately calculate storage fees for smart contracts using this formula:

  storage_fee = (cells_count * cell_price + bits_count * bit_price)
  * time_delta / 2^16

Let's examine each value more closely:

  • storage_fee—price for storage for time_delta seconds
  • cells_count—count of cells used by smart contract
  • bits_count—count of bits used by smart contract
  • cell_price—price of single cell
  • bit_price—price of single bit

Both cell_price and bit_price could be obtained from Network Config param 18.

Current values are:

  • Workchain.
    bit_price_ps:1
    cell_price_ps:500
  • Masterchain.
    mc_bit_price_ps:1000
    mc_cell_price_ps:500000

Calculator Example​

You can use this JS script to calculate storage price for 1 MB in the workchain for 1 year

Live Editor
Result
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Forward fees​

Internal messages define an ihr_fee in Toncoins, which is subtracted from the value attached to the message and awarded to the validators of the destination shardchain if they include the message by the IHR mechanism. The fwd_fee is the original total forwarding fee paid for using the HR mechanism; it is automatically computed from some configuration parameters and the size of the message at the time the message is generated. Notice that the total value carried by a newly-created internal outbound message equals the sum of value, ihr_fee, and fwd_fee. This sum is deducted from the balance of the source account. Of these components, only value is always credited to the destination account on message delivery. The fwd_fee is collected by the validators on the HR path from the source to the destination, and the ihr_fee is either collected by the validators of the destination shardchain (if the message is delivered via IHR), or credited to the destination account.

info

fwd_fee covers 2/3 of the cost, as 1/3 is allocated to the action_fee when the message is created.

auto fwd_fee_mine = msg_prices.get_first_part(fwd_fee);
auto fwd_fee_remain = fwd_fee - fwd_fee_mine;

fees_total = fwd_fee + ihr_fee;
fees_collected = fwd_fee_mine;

ap.total_action_fees += fees_collected;
ap.total_fwd_fees += fees_total;

Computation fees​

Gas​

All computation costs are nominated in gas units. The price of gas units is determined by this chain config (Config 20 for masterchain and Config 21 for basechain) and may be changed only by consensus of validators. Note that unlike in other systems, the user cannot set his own gas price, and there is no fee market.

Current settings in basechain are as follows: 1 unit of gas costs 400 nanotons.

TVM instructions cost​

On the lowest level (TVM instruction execution) the gas price for most primitives equals the basic gas price, computed as P_b := 10 + b + 5r, where b is the instruction length in bits and r is the number of cell references included in the instruction.

Apart from those basic fees, the following fees appear:

InstructionGAS priceDescription
Creation of cell500Operation of transforming builder to cell.
Parsing cell firstly100Operation of transforming cells into slices first time during current transaction.
Parsing cell repeatedly25Operation of transforming cells into slices, which already has parsed during same transaction.
Throwing exception50
Operation with tuple1This price will multiply by the quantity of tuple's elements.
Implicit Jump10It is paid when all instructions in the current continuation cell are executed. However, there are references in that continuation cell, and the execution flow jumps to the first reference.
Implicit Back Jump5It is paid when all instructions in the current continuation are executed and execution flow jumps back to the continuation from which the just finished continuation was called.
Moving stack elements1Price for moving stack elements between continuations. It will charge correspond gas price for every element. However, the first 32 elements moving is free.

FunC constructions gas fees​

Almost all FunC functions used in this article are defined in stablecoin stdlib.fc contract (actually, stdlib.fc with new opcodes is currently under development and not yet presented on the mainnet repos, but you can use stdlib.fc from stablecoin source code as reference) which maps FunC functions to Fift assembler instructions. In turn, Fift assembler instructions are mapped to bit-sequence instructions in asm.fif. So if you want to understand how much exactly the instruction call will cost you, you need to find asm representation in stdlib.fc, then find bit-sequence in asm.fif and calculate instruction length in bits.

However, generally, fees related to bit-lengths are minor in comparison with fees related to cell parsing and creation, as well as jumps and just number of executed instructions.

So, if you try to optimize your code start with architecture optimization, the decreasing number of cell parsing/creation operations, and then with the decreasing number of jumps.

Operations with cells​

Just an example of how proper cell work may substantially decrease gas costs.

Let's imagine that you want to add some encoded payload to the outgoing message. Straightforward implementation will be as follows:

slice payload_encoding(int a, int b, int c) {
  return
    begin_cell().store_uint(a,8)
                .store_uint(b,8)
                .store_uint(c,8)
    .end_cell().begin_parse();
}

() send_message(slice destination) impure {
  slice payload = payload_encoding(1, 7, 12);
  var msg = begin_cell()
    .store_uint(0x18, 6)
    .store_slice(destination)
    .store_coins(0)
    .store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
    .store_uint(0x33bbff77, 32) ;; op-code (see smart-contract guidelines)
    .store_uint(cur_lt(), 64)  ;; query_id (see smart-contract guidelines)
    .store_slice(payload)
  .end_cell();
  send_raw_message(msg, 64);
}

What is the problem with this code? payload_encoding to generate a slice bit-string, first create a cell via end_cell() (+500 gas units). Then parse it begin_parse() (+100 gas units). The same code can be written without those unnecessary operations by changing some commonly used types:

;; we add asm for function which stores one builder to the another, which is absent from stdlib
builder store_builder(builder to, builder what) asm(what to) "STB";

builder payload_encoding(int a, int b, int c) {
  return
    begin_cell().store_uint(a,8)
                .store_uint(b,8)
                .store_uint(c,8);
}

() send_message(slice destination) impure {
  builder payload = payload_encoding(1, 7, 12);
  var msg = begin_cell()
    .store_uint(0x18, 6)
    .store_slice(destination)
    .store_coins(0)
    .store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
    .store_uint(0x33bbff77, 32) ;; op-code (see smart-contract guidelines)
    .store_uint(cur_lt(), 64)  ;; query_id (see smart-contract guidelines)
    .store_builder(payload)
  .end_cell();
  send_raw_message(msg, 64);
}

By passing bit-string in the another form (builder instead of slice) we substantially decrease computation cost by very slight change in code.

Inline and inline_refs​

By default, when you have a FunC function, it gets its own id, stored in a separate leaf of id->function dictionary, and when you call it somewhere in the program, a search of the function in dictionary and subsequent jump occur. Such behavior is justified if your function is called from many places in the code and thus jumps allow to decrease the code size (by storing a function body once). However, if the function is only used once or twice, it is often much cheaper to declare this function as inline or inline_ref. inline modificator places the body of the function right into the code of the parent function, while inline_ref places the function code into the reference (jumping to the reference is still much cheaper than searching and jumping to the dictionary entry).

Dictionaries​

Dictionaries on TON are introduced as trees (DAGs to be precise) of cells. That means that if you search, read, or write to the dictionary, you need to parse all cells of the corresponding branch of the tree. That means that

  • a) dicts operations are not fixed in gas costs (since the size and number of nodes in the branch depend on the given dictionary and key)
  • b) it is expedient to optimize dict usage by using special instructions like replace instead of delete and add
  • c) developer should be aware of iteration operations (like next and prev) as well min_key/max_key operations to avoid unnecessary iteration through the whole dict

Stack operations​

Note that FunC manipulates stack entries under the hood. That means that the code:

(int a, int b, int c) = some_f();
return (c, b, a);

will be translated into a few instructions which changes the order of elements on the stack.

When the number of stack entries is substantial (10+), and they are actively used in different orders, stack operations fees may become non-negligible.

Action fee​

Action fee is deducted from the balance of the source account during processing action list which is perfomed after Computing phase. These are the actions that lead to pay fees:

  • SENDRAWMSG sends a raw message.
  • RAWRESERVE creates an output action which would reserve N Nanotons.
  • RAWRESERVEX similar to RAWRESERVE, but also accepts a dictionary with extra currencies.
  • SETCODE creates an output action that would change this smart contract code.
  • SETLIBCODE creates an output action that would modify the collection of this smart contract libraries by adding or removing library with given code.
  • CHANGELIB creates an output action similarly to SETLIBCODE, but instead of the library code accepts its hash.
  • FB08–FB3F reserved for output action primitives.

Fee's calculation formulas​

storage_fees​

storage_fees = ceil(
                    (account.bits * bit_price
                    + account.cells * cell_price)
               * period / 2 ^ 16)

in_fwd_fees, out_fwd_fees​

msg_fwd_fees = (lump_price
             + ceil(
                (bit_price * msg.bits + cell_price * msg.cells) / 2^16)
             )
             
ihr_fwd_fees = ceil((msg_fwd_fees * ihr_price_factor) / 2^16)
info

Only unique hash cells are counted for storage and fwd fees i.e. 3 identical hash cells are counted as one.

In particular, it deduplicates data: if there are several equivalent sub-cells referenced in different branches, their content is only stored once.

Read more about deduplication.

// bits in the root cell of a message are not included in msg.bits (lump_price pays for them)

action_fees​

action_fees = sum(out_ext_msg_fwd_fee) + sum(int_msg_mine_fee)

Fee's config file​

All fees are nominated in nanotons or nanotons multiplied by 2^16 to maintain accuracy while using integer and may be changed. The config file represents the current fee cost.

info

A direct link to the mainnet live config file

For educational purposes example of the old one

References​

  • Based on @thedailyton article from 24.07*

See Also​