Struct SessionMetrics 

pub struct SessionMetrics {

    pub jsonl_save: TimingCounter,
    pub jsonl_serialize: TimingCounter,
    pub jsonl_io: TimingCounter,
    pub jsonl_bytes: ByteCounter,
    pub jsonl_queue_wait: TimingCounter,
    pub sqlite_save: TimingCounter,
    pub sqlite_append: TimingCounter,
    pub sqlite_serialize: TimingCounter,
    pub sqlite_bytes: ByteCounter,
    pub sqlite_load: TimingCounter,
    pub sqlite_load_meta: TimingCounter,
    pub index_lock: TimingCounter,
    pub index_upsert: TimingCounter,
    pub index_list: TimingCounter,
    pub index_reindex: TimingCounter,
    pub append: TimingCounter,
    /* private fields */
}

Centralized session hot-path metrics collector.

Covers four key phases identified in the PERF-3X measurement plan:

1. Queueing: time between save request and actual IO start
2. Serialization: serde_json encoding time and output size
3. IO / Fsync: file write, flush, and atomic-rename time
4. Index update: session-index upsert time

Plus additional breakdowns for SQLite paths and lock contention.

Fields

jsonl_save: TimingCounter

Total wall-clock time for a complete Session::save() JSONL call.

jsonl_serialize: TimingCounter

Time spent in serde_json::to_writer for header + entries.

jsonl_io: TimingCounter

Time spent in BufWriter::flush() + tempfile::persist().

jsonl_bytes: ByteCounter

Bytes written per JSONL save (header + entries).

jsonl_queue_wait: TimingCounter

Queue wait: time from save() entry to IO thread start.

sqlite_save: TimingCounter

Total wall-clock time for save_session() (full rewrite).

sqlite_append: TimingCounter

Total wall-clock time for append_entries() (incremental append).

sqlite_serialize: TimingCounter

Time spent serializing entries to JSON strings within SQLite save.

sqlite_bytes: ByteCounter

Total JSON bytes produced during SQLite save serialization.

sqlite_load: TimingCounter

Total wall-clock time for load_session().

sqlite_load_meta: TimingCounter

Total wall-clock time for load_session_meta().

index_lock: TimingCounter

Lock acquisition time in SessionIndex::with_lock().

index_upsert: TimingCounter

Total wall-clock time for upsert_meta() (including lock).

index_list: TimingCounter

Total wall-clock time for list_sessions() (including lock).

index_reindex: TimingCounter

Total wall-clock time for reindex_all().

append: TimingCounter

Time for Session::append_message() and similar in-memory ops.

Implementations

impl SessionMetrics

pub fn enabled(&self) -> bool

Whether metrics collection is active.

pub fn enable(&self)

Explicitly enable metrics (useful for tests).

pub fn disable(&self)

Explicitly disable metrics.

pub fn start_timer<'a>(&'a self, counter: &'a TimingCounter) -> ScopedTimer<'a>

Start a scoped timer for counter. If metrics are disabled, returns a no-op timer that does nothing on drop.

pub fn record_bytes(&self, counter: &ByteCounter, bytes: u64)

Record bytes if metrics are enabled.

pub fn reset_all(&self)

Reset all counters to zero.

pub fn snapshot(&self) -> MetricsSnapshot

Produce a structured snapshot of all metrics.

pub fn summary(&self) -> String

Human-readable multi-line summary for diagnostics.

pub fn emit(&self)

Emit the summary to tracing::debug (called periodically or on demand).