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Overview

The update_global_config instruction allows the program authority to modify the global fee settings that apply to all SOL and SPL token transactions. Fees are specified in basis points (1 basis point = 0.01%).
Only the program authority can call this instruction. At least one parameter must be provided.

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Function Signature

pub fn update_global_config(
    ctx: Context<UpdateGlobalConfig>,
    deposit_fee_rate: Option<u16>,
    withdrawal_fee_rate: Option<u16>,
    fee_error_margin: Option<u16>
) -> Result<()>

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Parameters

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deposit_fee_rate
Option<u16>
Deposit fee rate in basis points (0-10000).
  • 0 = 0% (free deposits)
  • 25 = 0.25%
  • 100 = 1%
  • 1000 = 10%
  • 10000 = 100% (maximum)
Pass None to leave unchanged.
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withdrawal_fee_rate
Option<u16>
Withdrawal fee rate in basis points (0-10000).
  • 0 = 0% (free withdrawals)
  • 25 = 0.25% (default)
  • 50 = 0.5%
  • 100 = 1%
  • 10000 = 100% (maximum)
Pass None to leave unchanged.
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fee_error_margin
Option<u16>
Acceptable fee margin in basis points (0-10000). Allows fees to be within a range:
  • 0 = Exact fee required
  • 500 = ±5% (default)
  • 1000 = ±10%
Formula: expected_fee * (1 - margin/10000) <= actual_fee <= expected_feePass None to leave unchanged.

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Accounts

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global_config
Account<GlobalConfig>
required
Global configuration account. PDA: ["global_config"].
  • Mutable: Yes
  • Authority check: Must be owned by the signer
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authority
Signer
required
The program authority. Must match the global_config’s authority field.
  • Signer: Yes

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Code Examples

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Update Withdrawal Fee

import * as anchor from "@coral-xyz/anchor";
import { Program } from "@coral-xyz/anchor";
import { PublicKey } from "@solana/web3.js";

const program = anchor.workspace.Zkcash as Program<Zkcash>;
const authority = anchor.web3.Keypair.generate();

const [globalConfigPDA] = PublicKey.findProgramAddressSync(
  [Buffer.from("global_config")],
  program.programId
);

// Update withdrawal fee to 0.5% (50 basis points)
await program.methods
  .updateGlobalConfig(
    null, // Don't change deposit fee
    50,   // 0.5% withdrawal fee
    null  // Don't change error margin
  )
  .accounts({
    globalConfig: globalConfigPDA,
    authority: authority.publicKey
  })
  .signers([authority])
  .rpc();

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Update All Fee Settings

// Update all fee parameters at once
await program.methods
  .updateGlobalConfig(
    10,   // 0.1% deposit fee
    30,   // 0.3% withdrawal fee
    1000  // 10% error margin
  )
  .accounts({
    globalConfig: globalConfigPDA,
    authority: authority.publicKey
  })
  .signers([authority])
  .rpc();

console.log("All fee settings updated");

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Make Deposits Free

// Set deposit fee to 0%
await program.methods
  .updateGlobalConfig(
    0,    // Free deposits
    null, // Keep withdrawal fee unchanged
    null  // Keep error margin unchanged
  )
  .accounts({
    globalConfig: globalConfigPDA,
    authority: authority.publicKey
  })
  .signers([authority])
  .rpc();

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Fee Calculation Examples

With deposit fee rate of 25 basis points (0.25%):
Deposit: 10 SOL
Fee: 10 * 0.0025 = 0.025 SOL
User receives: 9.975 SOL in private balance
With withdrawal fee rate of 50 basis points (0.5%):
Withdrawal: 5 SOL
Fee: 5 * 0.005 = 0.025 SOL
User receives: 4.975 SOL
Fee recipient receives: 0.025 SOL
With error margin of 500 basis points (5%):
Expected fee: 0.025 SOL
Minimum acceptable: 0.025 * 0.95 = 0.02375 SOL
Maximum acceptable: 0.025 SOL (no upper bound)

This allows slightly lower fees to account for rounding errors.

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Basis Points Reference

Common Fee Rates

  • 0 = 0% (free)
  • 1 = 0.01%
  • 10 = 0.1%
  • 25 = 0.25%
  • 50 = 0.5%
  • 100 = 1%
  • 250 = 2.5%
  • 500 = 5%
  • 1000 = 10%

Fee Error Margins

  • 0 = No margin (exact)
  • 100 = ±1%
  • 500 = ±5%
  • 1000 = ±10%
  • 2000 = ±20%

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State Changes

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GlobalConfig

  • deposit_fee_rate: Updated if provided (otherwise unchanged)
  • withdrawal_fee_rate: Updated if provided (otherwise unchanged)
  • fee_error_margin: Updated if provided (otherwise unchanged)
All other fields remain unchanged.

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Behavior

  1. Validates each provided fee rate is ≤ 10000 (100%)
  2. Updates only the provided parameters
  3. Emits program log messages for each updated field
  4. Changes apply immediately to all subsequent transactions
Fee changes apply immediately. Ongoing transactions use the fee rates at the time of execution.

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Authorization

The signer must be the global config’s authority: 
#[account(
    mut,
    seeds = [b"global_config"],
    bump = global_config.bump,
    has_one = authority @ ErrorCode::Unauthorized
)]
pub global_config: Account<'info, GlobalConfig>,

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Errors

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Unauthorized
Error
Thrown when the signer is not the global config’s authority.
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InvalidFeeRate
Error
Thrown when any fee rate parameter exceeds 10000 (100%).

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Program Log Output

When successful, the instruction logs each updated field: 
Deposit fee rate updated to: {rate} basis points
Withdrawal fee rate updated to: {rate} basis points
Fee error margin updated to: {margin} basis points

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Reading Current Configuration

// Fetch current global config
const config = await program.account.globalConfig.fetch(globalConfigPDA);

console.log(`Deposit fee: ${config.depositFeeRate} basis points`);
console.log(`Withdrawal fee: ${config.withdrawalFeeRate} basis points`);
console.log(`Fee error margin: ${config.feeErrorMargin} basis points`);
console.log(`Authority: ${config.authority.toString()}`);

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Default Configuration

Initialized by the initialize instruction: 
deposit_fee_rate: 0,      // 0% - Free deposits
withdrawal_fee_rate: 25,  // 0.25%
fee_error_margin: 500,    // 5%

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Best Practices

1

Test fee changes

Test on devnet before updating mainnet configuration.
2

Announce changes

Notify users before making fee changes, especially increases.
3

Set reasonable margins

Use 5-10% error margins to account for precision and rounding.
4

Monitor impact

Track fee collection and transaction volume after changes.

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See Also

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