chore: Add metrics on types of filters in API (matter-labs#526)

## What ❔

Add metrics on types of filters, especially:
* Count of the current amount of filters of specific type
* Frequency of requests to specific filter type
* Lifetime of filters of specific type
* Request count for a specific filter

## Why ❔

We receive a lot of requests in our WebSocket API to getFilterChanges
method.

We want to understand types of filters and distribution of load among
them.

## Checklist

- [x] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [ ] Tests for the changes have been added / updated.
- [x] Documentation comments have been added / updated.
- [x] Code has been formatted via `zk fmt` and `zk lint`.

---------

Co-authored-by: Alex Ostrovski <[email protected]>

core/lib/web3_decl/src/types.rs

@@ -9,7 +9,6 @@ use core::convert::{TryFrom, TryInto};
 use core::fmt;
 use core::marker::PhantomData;
 
-use chrono::NaiveDateTime;
 use itertools::unfold;
 use rlp::Rlp;
 use serde::{de, Deserialize, Serialize, Serializer};
@@ -105,14 +104,6 @@ pub enum FilterChanges {
     Empty([u8; 0]),
 }
 
-/// Represents all kinds of `Filter`.
-#[derive(Debug, Clone)]
-pub enum TypedFilter {
-    Events(Filter, zksync_types::MiniblockNumber),
-    Blocks(zksync_types::MiniblockNumber),
-    PendingTransactions(NaiveDateTime),
-}
-
 /// Either value or array of values.
 #[derive(Default, Debug, PartialEq, Clone)]
 pub struct ValueOrArray<T>(pub Vec<T>);

core/lib/zksync_core/src/api_server/web3/metrics.rs

@@ -2,18 +2,17 @@
 
 use vise::{
     Buckets, Counter, EncodeLabelSet, EncodeLabelValue, Family, Gauge, Histogram, LabeledFamily,
-    LatencyObserver, Metrics,
+    LatencyObserver, Metrics, Unit,
 };
 
 use std::{
     fmt,
     time::{Duration, Instant},
 };
 
+use super::{ApiTransport, TypedFilter};
 use zksync_types::api;
 
-use super::ApiTransport;
-
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, EncodeLabelValue, EncodeLabelSet)]
 #[metrics(label = "scheme", rename_all = "UPPERCASE")]
 pub(super) enum ApiTransportLabel {
@@ -195,3 +194,40 @@ pub(super) struct PubSubMetrics {
 
 #[vise::register]
 pub(super) static PUB_SUB_METRICS: vise::Global<PubSubMetrics> = vise::Global::new();
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, EncodeLabelValue, EncodeLabelSet)]
+#[metrics(label = "type", rename_all = "snake_case")]
+pub(super) enum FilterType {
+    Events,
+    Blocks,
+    PendingTransactions,
+}
+
+impl From<&TypedFilter> for FilterType {
+    fn from(value: &TypedFilter) -> Self {
+        match value {
+            TypedFilter::Events(_, _) => FilterType::Events,
+            TypedFilter::Blocks(_) => FilterType::Blocks,
+            TypedFilter::PendingTransactions(_) => FilterType::PendingTransactions,
+        }
+    }
+}
+
+#[derive(Debug, Metrics)]
+#[metrics(prefix = "api_web3_filter")]
+pub(super) struct FilterMetrics {
+    /// Number of currently active filters grouped by the filter type
+    pub metrics_count: Family<FilterType, Gauge>,
+    /// Time in seconds between consecutive requests to the filter grouped by the filter type
+    #[metrics(buckets = Buckets::LATENCIES, unit = Unit::Seconds)]
+    pub request_frequency: Family<FilterType, Histogram<Duration>>,
+    /// Lifetime of a filter in seconds grouped by the filter type
+    #[metrics(buckets = Buckets::LATENCIES, unit = Unit::Seconds)]
+    pub filter_lifetime: Family<FilterType, Histogram<Duration>>,
+    /// Number of requests to the filter grouped by the filter type
+    #[metrics(buckets = Buckets::exponential(1.0..=1048576.0, 2.0))]
+    pub filter_count: Family<FilterType, Histogram<usize>>,
+}
+
+#[vise::register]
+pub(super) static FILTER_METRICS: vise::Global<FilterMetrics> = vise::Global::new();

core/lib/zksync_core/src/api_server/web3/mod.rs

@@ -4,9 +4,10 @@ use jsonrpc_core::MetaIoHandler;
 use jsonrpc_http_server::hyper;
 use jsonrpc_pubsub::PubSubHandler;
 use serde::Deserialize;
-use tokio::sync::{oneshot, watch, RwLock};
+use tokio::sync::{oneshot, watch, Mutex};
 use tower_http::{cors::CorsLayer, metrics::InFlightRequestsLayer};
 
+use chrono::NaiveDateTime;
 use std::{net::SocketAddr, sync::Arc, time::Duration};
 use tokio::task::JoinHandle;
 
@@ -23,6 +24,7 @@ use zksync_web3_decl::{
         DebugNamespaceServer, EnNamespaceServer, EthNamespaceServer, NetNamespaceServer,
         Web3NamespaceServer, ZksNamespaceServer,
     },
+    types::Filter,
 };
 
 use crate::{
@@ -63,6 +65,17 @@ use self::state::{Filters, InternalApiConfig, RpcState, SealedMiniblockNumber};
 /// Timeout for graceful shutdown logic within API servers.
 const GRACEFUL_SHUTDOWN_TIMEOUT: Duration = Duration::from_secs(5);
 
+/// Represents all kinds of `Filter`.
+#[derive(Debug, Clone)]
+pub(crate) enum TypedFilter {
+    // Events from some block with additional filters
+    Events(Filter, MiniblockNumber),
+    // Blocks from some block
+    Blocks(MiniblockNumber),
+    // Pending transactions from some timestamp
+    PendingTransactions(NaiveDateTime),
+}
+
 #[derive(Debug, Clone, Copy)]
 enum ApiBackend {
     Jsonrpsee,
@@ -278,7 +291,7 @@ impl<G: 'static + Send + Sync + L1GasPriceProvider> ApiBuilder<G> {
         tokio::spawn(update_task);
 
         RpcState {
-            installed_filters: Arc::new(RwLock::new(Filters::new(
+            installed_filters: Arc::new(Mutex::new(Filters::new(
                 self.filters_limit.unwrap_or(usize::MAX),
             ))),
             connection_pool: self.pool,