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Overview

Slot messages provide updates about slot progression and status changes on the Solana blockchain. Slots are the fundamental unit of time in Solana, occurring approximately every 400ms.

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SubscribeUpdateSlot

Slot status update message. 
message SubscribeUpdateSlot {
  uint64 slot = 1;
  optional uint64 parent = 2;
  SlotStatus status = 3;
  optional string dead_error = 4;
}

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Fields

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slot
uint64
required
The slot number being updated.
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parent
uint64
The parent slot number. Most slots have a parent, but this field may be absent in certain edge cases (e.g., genesis slot).
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status
SlotStatus
required
The current status of this slot. See SlotStatus below for possible values.
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dead_error
string
Error message if the slot is marked as dead (status = SLOT_DEAD). Describes why the slot was abandoned. Empty for other statuses.

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Examples

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Processed Slot

{
  "slot": 250000000,
  "parent": 249999999,
  "status": "SLOT_PROCESSED"
}

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Confirmed Slot

{
  "slot": 250000000,
  "parent": 249999999,
  "status": "SLOT_CONFIRMED"
}

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Finalized Slot

{
  "slot": 250000000,
  "parent": 249999999,
  "status": "SLOT_FINALIZED"
}

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Dead Slot

{
  "slot": 250000000,
  "parent": 249999999,
  "status": "SLOT_DEAD",
  "dead_error": "TooManyDuplicateShreds"
}

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SlotStatus

Enum defining the possible states of a slot. 
enum SlotStatus {
  SLOT_PROCESSED = 0;
  SLOT_CONFIRMED = 1;
  SLOT_FINALIZED = 2;
  SLOT_FIRST_SHRED_RECEIVED = 3;
  SLOT_COMPLETED = 4;
  SLOT_CREATED_BANK = 5;
  SLOT_DEAD = 6;
}

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Status Values

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SLOT_PROCESSED
0
The slot has been processed by a validator. This is the earliest status indicating that transactions in this slot have been executed. May still be subject to rollback.
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SLOT_CONFIRMED
1
The slot has been confirmed by a supermajority of the cluster. More reliable than processed, but still potentially subject to rollback in extreme circumstances.
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SLOT_FINALIZED
2
The slot has been finalized (rooted). This is the final state for a valid slot. Once finalized, a slot is permanent and cannot be rolled back.
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SLOT_FIRST_SHRED_RECEIVED
3
The first shred (packet of data) for this slot has been received. This is the earliest signal that work on a slot has begun. Only sent if you enable interslot_updates in your slot filter.
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SLOT_COMPLETED
4
All shreds for the slot have been received and the slot is complete. Only sent if you enable interslot_updates in your slot filter.
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SLOT_CREATED_BANK
5
A bank (execution context) has been created for this slot. Only sent if you enable interslot_updates in your slot filter.
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SLOT_DEAD
6
The slot has been marked as dead and abandoned. This can happen for various reasons (e.g., fork, duplicate shreds, validator errors). Check the dead_error field for details.

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Status Progression

Slots typically progress through these states:
  1. SLOT_FIRST_SHRED_RECEIVED (if interslot_updates enabled) - First data received
  2. SLOT_CREATED_BANK (if interslot_updates enabled) - Execution context created
  3. SLOT_COMPLETED (if interslot_updates enabled) - All data received
  4. SLOT_PROCESSED - Transactions executed
  5. SLOT_CONFIRMED - Confirmed by supermajority
  6. SLOT_FINALIZED - Permanently finalized
Alternatively, at any point:
  • SLOT_DEAD - Slot abandoned

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Subscription Options

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Basic Slot Subscription

Receive only major status updates (processed, confirmed, finalized): 
{
  "slots": {
    "all_slots": {}
  },
  "commitment": "CONFIRMED"
}

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Commitment-Filtered Slots

Receive only updates matching your commitment level: 
{
  "slots": {
    "finalized_only": {
      "filter_by_commitment": true
    }
  },
  "commitment": "FINALIZED"
}

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Inter-Slot Updates

Receive all status updates including intermediate states: 
{
  "slots": {
    "detailed_slots": {
      "interslot_updates": true
    }
  }
}

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Both Options Combined

{
  "slots": {
    "filtered_detailed": {
      "filter_by_commitment": true,
      "interslot_updates": true
    }
  },
  "commitment": "CONFIRMED"
}

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Use Cases

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Tracking Chain Progress

Monitor slot progression to track blockchain progress: 
if (update.slot) {
  const slot = update.slot;
  console.log(`Slot ${slot.slot}: ${slot.status}`);
  
  if (slot.status === 'SLOT_FINALIZED') {
    console.log(`Slot ${slot.slot} is now permanent`);
  }
}

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Detecting Forks and Rollbacks

Monitor dead slots to detect potential chain issues: 
if (update.slot && update.slot.status === 'SLOT_DEAD') {
  console.warn(`Slot ${update.slot.slot} was abandoned: ${update.slot.dead_error}`);
  // Handle potential rollback
}

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Measuring Slot Timing

Use inter-slot updates to measure slot production timing: 
const slotTiming = {};

if (update.slot) {
  const slot = update.slot.slot;
  const status = update.slot.status;
  
  if (!slotTiming[slot]) {
    slotTiming[slot] = {};
  }
  
  slotTiming[slot][status] = Date.now();
  
  if (status === 'SLOT_FINALIZED' && slotTiming[slot]['SLOT_FIRST_SHRED_RECEIVED']) {
    const duration = slotTiming[slot]['SLOT_FINALIZED'] - slotTiming[slot]['SLOT_FIRST_SHRED_RECEIVED'];
    console.log(`Slot ${slot} took ${duration}ms from first shred to finalization`);
  }
}

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Commitment-Based Processing

Process data based on slot commitment level: 
if (update.slot) {
  const slot = update.slot;
  
  switch (slot.status) {
    case 'SLOT_PROCESSED':
      // Fast but potentially unstable data
      console.log('Processing slot data (may rollback)');
      break;
    case 'SLOT_CONFIRMED':
      // More stable data
      console.log('Confirmed slot data (unlikely to rollback)');
      break;
    case 'SLOT_FINALIZED':
      // Permanent data
      console.log('Finalized slot data (permanent)');
      break;
  }
}

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Understanding Slot vs Block

  • Slot: A fixed time period (~400ms) in which a leader validator can produce a block
  • Block: The actual data produced during a slot
Not all slots produce blocks (a slot can be skipped), but when they do, the block number equals the slot number.

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