ValidatorPruneLenSet

Event Re-added v101 → v127, v133 → v219, v233 → v265, v273 → v277, v290 → current #20

Emitted when validator prune length is changed.

Useful for: validatorssubnet ownersanalyticsdevelopers

The Big Picture

When subnets are full and new validators want to join, existing validators may be pruned (removed) to make room. The validator prune length controls how many of the worst-performing validators are considered for pruning. A longer prune length means more validators are 'at risk' - even mid-tier validators could be pruned. A shorter length means only the absolute worst performers face removal. This affects how competitive and stable the validator set is.

Why This Matters

As a validator, prune length determines your safety margin. With a short prune length, you only risk removal if you're in the bottom few. With a long prune length, even average performance might not be safe. This affects how aggressively you need to compete.

Example Scenario

Subnet 8 has 64 validators and ValidatorPruneLen was 4 (only bottom 4 at risk). The owner wants more competition and increases it to 16. ValidatorPruneLenSet fires. Now bottom 25% of validators are at risk instead of bottom 6%. Mid-tier validators who felt safe now face real pruning pressure.

Common Questions

When does pruning actually happen?: Pruning happens when new validators want to register on a full subnet. The registration mechanism checks the prune length to determine which validators can be replaced.
How is 'worst performing' determined?: Typically by stake or consensus weight. Validators with less stake or lower consensus scores are considered worse performing. Check your subnet's specific pruning criteria.
Can I avoid pruning with more stake?: Usually yes. Higher stake typically moves you up in the validator ranking, away from the prune zone. Performance also matters - stake alone may not save a very poor performer.

Use Cases

Monitor validator pruning policy changes
Understand validator slot competition dynamics
Plan validator strategy around pruning rules
Analyze validator turnover rates

How to Use This Event

→ Monitor prune length on subnets where you validate
→ Track changes that affect validator stability
→ Analyze validator turnover patterns

From Chain Metadata

the validator pruning length has been set.

Triggers

Preconditions

Caller has admin/sudo privileges
New length is within valid range

Effects

Postconditions

ValidatorPruneLen updated for subnet
Pruning mechanism uses new length

Side Effects

Affects how many validators considered for pruning
May increase or decrease validator turnover

Event Data

#	Name	Type	Description
0	arg0	u16	Event field #0 (u16)
1	arg1	u64	Event field #1 (u64)

Code Examples

import { ApiPromise, WsProvider } from "@polkadot/api";
import { stringCamelCase } from "@polkadot/util";

const provider = new WsProvider("wss://entrypoint-finney.opentensor.ai:443");
const api = await ApiPromise.create({ provider });

// Subscribe to ValidatorPruneLenSet events
api.query.system.events((events) => {
  events
    .filter(({ event }) =>
      event.section === stringCamelCase("SubtensorModule") &&
      event.method === "ValidatorPruneLenSet"
    )
    .forEach(({ event }) => {
      console.log("ValidatorPruneLenSet:", event.data.toHuman());
    });
});

Version History

Version:

v101 block 1 2 args

v133 block 1,404,224 2 args

v233 block 4,920,350 2 args

v273 block 5,659,032 2 args

v290 block 5,947,548 2 args Current

Runtime Info

View Source

Pallet Index: 7
Event Index: 20
First Version: v101
Current Version: v393

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