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Avoid BeaconState clone during metrics scrape (#2298)

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## Issue Addressed

Which issue # does this PR address?

## Proposed Changes

Avoids cloning the `BeaconState` each time Prometheus scrapes our metrics (generally every 5s 😱).

I think the original motivation behind this was *"don't hold the lock on the head whilst we do computation on it"*, however I think is flawed since our computation here is so small that it'll be quicker than the clone.

The primary motivation here is to maintain a small memory footprint by holding less in memory (i.e., the cloned `BeaconState`) and to avoid the fragmentation-creep that occurs when cloning the big contiguous slabs of memory in the `BeaconState`.

I also collapsed the active/slashed/withdrawn counters into a single loop to increase efficiency.

## Additional Info

NA
This commit is contained in:
Paul Hauner 2021-04-07 01:02:56 +00:00
parent 66590d043c
commit e7e5878953
1 changed files with 29 additions and 26 deletions
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55
beacon_node/beacon_chain/src/metrics.rs
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@ -1,4 +1,4 @@
use crate::{BeaconChain, BeaconChainTypes};
use crate::{BeaconChain, BeaconChainError, BeaconChainTypes};
use lazy_static::lazy_static;
pub use lighthouse_metrics::*;
use slot_clock::SlotClock;
@ -643,9 +643,10 @@ lazy_static! {
/// Scrape the `beacon_chain` for metrics that are not constantly updated (e.g., the present slot,
/// head state info, etc) and update the Prometheus `DEFAULT_REGISTRY`.
pub fn scrape_for_metrics<T: BeaconChainTypes>(beacon_chain: &BeaconChain<T>) {
if let Ok(head) = beacon_chain.head() {
scrape_head_state::<T>(&head.beacon_state, head.beacon_state_root())
}
let _ = beacon_chain.with_head(|head| {
scrape_head_state(&head.beacon_state, head.beacon_state_root());
Ok::<_, BeaconChainError>(())
});
if let Some(slot) = beacon_chain.slot_clock.now() {
scrape_attestation_observation(slot, beacon_chain);
@ -675,7 +676,7 @@ pub fn scrape_for_metrics<T: BeaconChainTypes>(beacon_chain: &BeaconChain<T>) {
}
/// Scrape the given `state` assuming it's the head state, updating the `DEFAULT_REGISTRY`.
fn scrape_head_state<T: BeaconChainTypes>(state: &BeaconState<T::EthSpec>, state_root: Hash256) {
fn scrape_head_state<T: EthSpec>(state: &BeaconState<T>, state_root: Hash256) {
set_gauge_by_slot(&HEAD_STATE_SLOT, state.slot);
set_gauge_by_hash(&HEAD_STATE_ROOT, state_root);
set_gauge_by_slot(
@ -703,29 +704,31 @@ fn scrape_head_state<T: BeaconChainTypes>(state: &BeaconState<T::EthSpec>, state
&HEAD_STATE_FINALIZED_EPOCH,
state.finalized_checkpoint.epoch,
);
set_gauge_by_u64(&HEAD_STATE_ETH1_DEPOSIT_INDEX, state.eth1_deposit_index);
set_gauge_by_usize(&HEAD_STATE_TOTAL_VALIDATORS, state.validators.len());
set_gauge_by_u64(&HEAD_STATE_VALIDATOR_BALANCES, state.balances.iter().sum());
set_gauge_by_usize(
&HEAD_STATE_ACTIVE_VALIDATORS,
state
.validators
.iter()
.filter(|v| v.is_active_at(state.current_epoch()))
.count(),
);
set_gauge_by_usize(
&HEAD_STATE_SLASHED_VALIDATORS,
state.validators.iter().filter(|v| v.slashed).count(),
);
set_gauge_by_usize(
&HEAD_STATE_WITHDRAWN_VALIDATORS,
state
.validators
.iter()
.filter(|v| v.is_withdrawable_at(state.current_epoch()))
.count(),
);
set_gauge_by_u64(&HEAD_STATE_ETH1_DEPOSIT_INDEX, state.eth1_deposit_index);
let mut num_active: usize = 0;
let mut num_slashed: usize = 0;
let mut num_withdrawn: usize = 0;
for v in &state.validators {
if v.is_active_at(state.current_epoch()) {
num_active += 1;
}
if v.slashed {
num_slashed += 1;
}
if v.is_withdrawable_at(state.current_epoch()) {
num_withdrawn += 1;
}
}
set_gauge_by_usize(&HEAD_STATE_ACTIVE_VALIDATORS, num_active);
set_gauge_by_usize(&HEAD_STATE_SLASHED_VALIDATORS, num_slashed);
set_gauge_by_usize(&HEAD_STATE_WITHDRAWN_VALIDATORS, num_withdrawn);
}
fn scrape_attestation_observation<T: BeaconChainTypes>(slot_now: Slot, chain: &BeaconChain<T>) {